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Northern Australia Land and Water Science Review full report October 2009 03 Aquatic ecosystems in northern Australia Bradley J Pusey, Tropical Rivers and Coastal Knowledge (TRaCK) Commonwealth Environmental Research Facility, Australian Rivers Institute, Griffith University. [email protected] Mark J Kennard, Tropical Rivers and Coastal Knowledge (TRaCK) Commonwealth Environmental Research Facility, Australian Rivers Institute, Griffith University. [email protected] Butler’s grunter (Syncomistes butleri) juvenile (main picture) and adult (inset picture). This species is endemic to a few rivers in northern Australia and may be at high risk from dry season water extraction. Photos: Neil Armstrong Aquatic ecosystems in northern Australia Chapter 3 ‐ 1
Northern Australia Land and Water Science Review full report October 2009 CONTENTS 1 KEY POINTS ........................................................................................................................................... 4 1.1 INTRODUCTION ................................................................................................................................. 4 1.2 WHAT ARE AQUATIC ECOSYSTEMS? .......................................................................................... 4 1.3 WHAT IS A HYDROLOGICAL REGIME AND WHY IS IT IMPORTANT?........................................... 5 1.4 THE TYPES OF HYDROSYSTEMS PRESENT IN NORTHERN AUSTRALIA...................................... 12 1.4.1 Estuarine hydrosystems....................................................................................................... 12 1.4.2 Riverine hydrosystems......................................................................................................... 16 1.4.3 Lacustrine (lake) hydrosystems ........................................................................................... 19 1.4.4 Palustrine (floodplain) hydrosystems .................................................................................. 20 1.4.5 Subterranean (groundwater) hydrosystems........................................................................ 25 1.4.6 Artificial hydrosystems......................................................................................................... 25 1.4.7 Riparian zones...................................................................................................................... 30 1.5 THE CURRENT CONDITION OF NORTHERN AUSTRALIAN AQUATIC ECOSYSTEMS................... 35 1.6 CHANGES IN AQUATIC ECOSYSTEMS IN RESPONSE TO ALTERED FLOW REGIMES.................. 41 1.6.1 Groundwater and riparian extraction – ecological impacts of reduced water levels ......... 41 1.6.2 Physical infrastructure (dams, weirs, tidal barrages, pipes, canals and road crossings) – barriers to movement, transformation of riverine habitat, translocation of plants and animals .... 45 1.6.3 Wet season floods – impacts of large dams and flood harvesting ...................................... 48 1.6.4 Dry season flow supplementation – flow releases from dam ............................................. 49 1.6.5 Ecological impacts of climate change .................................................................................. 49 1.7 CHANGES IN AQUATIC ECOSYSTEMS IN RESPONSE TO OTHER HUMAN ACTIVITIES ............... 51 1.7.1 Agriculture (including broad‐acre and mosaic).................................................................... 51 1.7.2 Rangeland and high‐density cattle production.................................................................... 53 1.7.3 Mining and other extractive industries................................................................................ 54 1.7.4 Tourism and recreation........................................................................................................ 54 1.7.5 Urbanisation......................................................................................................................... 57 1.8 ASSESSMENT OF POTENTIAL ECOLOGICAL CONSEQUENCES OF FLOW REGIME CHANGES UNDER FUTURE CLIMATE AND DEVELOPMENT SCENARIOS FOR KEY ENVIRONMENTAL ASSETS IN THREE CASE STUDY RIVERS ................................................................................................................... 57 1.8.1 Fitzroy River at Camballin Weir ........................................................................................... 58 1.8.2 Daly River at Oolloo Crossing............................................................................................... 58 1.8.3 Mitchell River Fan Aggregation............................................................................................ 59 1.9 WHAT ARE THE POSITIVE AND INTENDED OUTCOMES ARISING FROM CHANGES TO FLOW REGIMES? .............................................................................................................................................. 60 Aquatic ecosystems in northern Australia Chapter 3 ‐ 2
Northern Australia Land and Water Science Review full report October 2009 1.10 IF CHANGES IN WATER REGIME WERE TO OCCUR, WHAT WOULD BE REQUIRED TO MINIMISE THE NEGATIVE IMPACTS ON AQUATIC ECOSYSTEMS? ......................................................................... 61 1.11 WHAT ARE THE CRITICAL KNOWLEDGE GAPS PREVENTING SOUND ANSWERS TO QUESTIONS ABOVE?.................................................................................................................................................. 63 1.12 SUMMARY ................................................................................................................................ 64 1.12.1 What are the critical links between aquatic ecology and development of northern Australia? 64 1.12.2 What is the current status of aquatic ecosystems? ........................................................ 64 1.12.3 What is the immediate prognosis of the health of northern Australian aquatic ecosystems? ...................................................................................................................................... 65 1.12.4 What are the likely future pressures or trajectories? ..................................................... 65 1.13 ACKNOWLEDGMENTS .............................................................................................................. 65 1.14 REFERENCES ............................................................................................................................. 66 Feature Boxes Box 1: The Norman River estuary – tides, tourists and tucker Box 2: Wasted water? – Fisheries catch information demonstrates otherwise Box 3: Water birds, wetlands and international avian and human visitors Box 4: Magpie geese – icons of the north Box 5: Rivers and reptiles Box 6: Groundwater fauna – unseen biodiversity and role in aquatic ecosystems Box 7: Going against the flow – dams in northern Australia Box 8: The Ord River – a cautionary tale Box 9: Food webs – who’s eating what? Box 10: Riparian zones – sustaining the rich bird fauna of the north Box 11: Dine in or out – riparian contributions to food webs Box 12: The twilight zone – alien invasions Box 13: The Daly – fish out of water? Aquatic ecosystems in northern Australia Chapter 3 ‐ 3
Northern Australia Land and Water Science Review full report October 2009 1 KEY POINTS 1. Northern Australia hosts a range of aquatic ecosystem types (estuaries, rivers, lakes, wetlands) supporting high biodiversity and many endemic species of aquatic plants and animals. Most aquatic ecosystems are currently in very good ecological condition but are, in some cases, threatened by invasive weeds and alien terrestrial pests such as pigs and buffalo. 2. The ecology and condition of northern aquatic ecosystems is intimately dependent on the nature of the flow regime. 3. Current water infrastructure, water use and agricultural land use has had demonstrative negative effects on aquatic ecosystems but these have been limited in spatial scale, with the exception of cattle grazing. Northern Australian aquatic ecosystems are numerically underrepresented in Commonwealth conservation and management inventories (i.e. RAMSAR, Directory of Important Wetlands). 4. A diversity of flow regime types occurs across northern Australia which when coupled with spatial diversity in fluvial landscape structure and diversity of aquatic ecosystem types result in a diversity of ways in which future water development may impact on aquatic systems. 5. Critical knowledge gaps exist concerning the key environmental drivers of aquatic ecosystems. Improved knowledge will allow scientists and managers to predict with greater certainty the responses of aquatic ecosystem responses to future environmental changes associated with water use, land use and climate change. 1.1 INTRODUCTION Natural functioning aquatic ecosystems have important intrinsic and cultural values and provide many goods, services and long‐term benefits to human society (1, 2). This chapter concerns the nature and future of aquatic ecosystems present in northern Australia. We describe the main types of ecosystems, illustrate the diversity of plants and animals within them and highlight the natural physical, hydrological and ecological processes that sustain these important assets of northern Australia. We evaluate the current condition and existing threats to aquatic ecosystems across northern Australia and describe the manner in which future human activities and climate change may impact upon them. Specific issues are highlighted using case study examples from three key catchments in northern Australia: the Fitzroy River in the Kimberley region, the Daly River in the Northern Territory and the Mitchell River in the northern Gulf region of Queensland. A series of feature boxes highlight the characteristics of particular plant and animal groups, important habitats, and key threatening processes. We also outline the critical knowledge gaps that currently hinder sustainable management and conservation of aquatic ecosystems in northern Australia. Natural aquatic ecosystems have important intrinsic and cultural values and provide many goods, services and long‐term benefits to human society 1.2 WHAT ARE AQUATIC ECOSYSTEMS? Aquatic ecosystems can be defined as those ecological systems that are primarily shaped and sustained by the permanent or temporary presence of water. The key point here is that the hydrological regime shapes and maintains aquatic ecosystems and variations in hydrology influence their physical and biological characteristics. Aquatic ecosystems can be classified broadly into different types known as ‘hydrosystems’ (3). These are large ‘organising entities’ designed to represent the variety of aquatic ecosystem types (e.g. estuaries, rivers, lakes). Hydrosystems can consist of one ecotope (the smallest ecologically‐distinct features in a landscape classification Aquatic ecosystems in northern Australia Chapter 3 ‐ 4
Northern Australia Land and Water Science Review full report October 2009 system) or an aggregation of ecotopes. For example, a complex of swamps along a river floodplain can be regarded as a single hydrosystem. This classification scheme emphasizes the connectivity between the different ecosystem types, a critical feature in aquatic ecology, and their dependence on the amount and temporal availability of the water that sustains them. The types of hydrosystems (and their constituent ecotopes) addressed in this chapter are listed Table 1 (note that marine and coastal foreshore hydrosystems are not considered in this Chapter). Table 1. Northern Australian hydrosystems and their associated aquatic ecosystem types. (after Mount et al. (3)). Hydrosystem Ecotope types present in northern Australia Estuarine Semi‐enclosed embayments receiving sea water and fresh water inputs, mangrove forests, saltmarshes, saltflats, intertidal flats. Riverine Rivers and streams (but not including the hyporheic zone) Lacustrine Lakes formed by previous river channel migration (i.e. oxbow lakes, lagoons and billabongs). Palustrine Floodplains and vegetated wetlands such as marshes, bogs and swamps, and including small, shallow, permanent or intermittent water bodies. Subterranean Groundwater environments including the hyporheic zone and underground streams, lakes and water‐filled voids Artificial Reservoirs, farm dams, mine tailings dams, flood irrigated field, canals and drainage channels 1.3 WHAT IS A HYDROLOGICAL REGIME AND WHY IS IT IMPORTANT? Ecologists and environmental managers increasingly recognize that the natural hydrological (flow) regime is the fundamental driver of processes that shape the physical and ecological nature of aquatic ecosystems (4). Critical components of the natural flow regime include the magnitude and seasonal pattern of flows; timing of extreme flows; the frequency, predictability, and duration of floods, droughts, and intermittent flows; daily, seasonal, and annual flow variability; and rates of change in flow events (4, 5; Fig. 1). Spatial variation in these hydrologic characteristics is determined by variations in climate and mediated by catchment geology, topography and vegetation (6). These factors interact at multiple spatial and temporal scales to influence connectivity between hydrosystems, physical habitat for aquatic and riparian biota, the availability of refuges, the distribution of food resources, opportunities for movement and migration, and conditions suitable for reproduction and recruitment (7). Aquatic ecosystems in northern Australia Chapter 3 ‐ 5
Northern Australia Land and Water Science Review full report October 2009 Flow regime
Flow history
Flow pulse
Seasonal timing
Inter-annual variability & predictability
Flood magnitude
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Figure 1. Different components of the natural flow regime are ecologically important over a range of temporal scales. The maintenance of these key components of the natural flow regime is critical to protecting and maintaining freshwater biodiversity, natural ecological processes, and the essential goods and services provided by aquatic ecosystems (5). For example, variation in river flow influences the transmission of materials and energy through aquatic food webs within and between different parts of the aquatic ecosystem (e.g. between groundwater and surface water and between, headwaters, main channel, floodplain and estuaries). This is critical to the maintenance of biodiversity and the natural functioning of aquatic ecosystems (see Boxes 1 and 2). Similarly, variations in flow regimes drive variation in physical habitat structure, a key determinant of the types and rates of organic matter production and transmission, as well as the abundance and diversity of aquatic plants and animals The maintenance of the natural flow regime and connectivity between aquatic ecosystems is critical for sustaining freshwater biodiversity and natural ecological processes Aquatic ecosystems in northern Australia Chapter 3 ‐ 6
Northern Australia Land and Water Science Review full report October 2009 Box 1: The Norman River estuary – tides, tourists and tucker Australia has more than 1,000 estuaries along its 36,700 km of coastline. Estuaries are highly productive and diverse habitats supporting fisheries, aquaculture, ports and recreational activities. They are dynamic systems linking catchments, rivers and inshore marine waters (8). The Norman River estuary, situated in the southern Gulf of Carpentaria, is home to a significant commercial fishing fleet (Fig. 1.1) and is an important tourist destination during the winter months. Recreational fishers make up the bulk of visitors, targeting such species as barramundi, grunter and mud crabs (Fig. 1.2). Figure 1.1. Fishing boats tied up at the docks while their catch is processed. Photo: M. Burford. The estuary system is a tide‐dominated delta (0.7 km wide at the mouth), largely unmodified by human activity, and consists of a main river channel with a few secondary tidal creeks. The nature of the estuary and the biological processes occurring within it are tightly associated with the seasonal hydrological cycle. During the dry season, the salinity wedge extends as far as the township of Normanton, 80 km upstream of the coastal town of Karumba. The 4 m tidal range results in exposure of a ~5‐10 m wide strip of 2
mudflats (24 km ) and an adjacent narrow strip of small, sparse 2
mangrove forest (40 km in total). Behind the mangroves are 2
extensive sparsely vegetated saltflat areas (200 km ) that are dry most of the time. During the dry season, the amount of estuarine habitat is greatly reduced compared to the wet season. Over shorter time scales, tidal fluxes in water depth result in further fluctuations in habitat area and, in the case of juvenile fishes denied the protection of tidally exposed mangroves, greatly increases predation risk. During the summer monsoon, large episodic rainfall events, e.g. cyclones, deposit massive volumes of water onto the catchment that are carried down into the estuary with associated loads of sediment, organic matter and dissolved nutrients. The lower catchment may become flooded for weeks or months. In very wet summers, the volume of freshwater is sufficiently large to flood all of the coastal saltflats and create a vast area of shallow, highly productive habitat connected to the mangrove forests and the estuary. Aquatic ecosystems in northern Australia Figure 1.2. A very lucky American tourist with his first barramundi. Photo:
B. Pusey. The estuary is an important nursery ground for juvenile prawns
during the wet season, with this habitat providing food and refuge
from predators. These prawns migrate offshore as they reach
adulthood and are the basis for a major commercial prawn fishery
in the Gulf of Carpentaria. Previous studies in the Gulf of
Carpentaria and elsewhere in northern Australia have established
that wet seasons with higher flow result in a higher catch of
prawns and a range of fish species (see Box 2). The estuary is also an important nursery ground for a large range
of fish species. Larvae and juvenile fish are highly abundant on the
inundated salt flats and move into the mangrove forests as they
grow. The shallow waters of the saltflats afford them some
protection against predators as well as providing large amounts of
small invertebrate food. The tangled roots of the mangrove forests
also provide vital refuge from larger predatory fishes (Fig. 1.3). Figure 1.4 shows a simple conceptual model of the way in which
human activities that change the amount and timing of fresh
inputs into the estuary affect primary and secondary production
and ultimately the abundance of commercially and recreationally
significant species (therein referred to as goods and services). Chapter 3 ‐ 7
Northern Australia Land and Water Science Review full report October 2009 Box 1: The Norman River estuary – tides, tourists and tucker Water regulation
(e.g. dams)
Water extraction
Effects on
hydrology
Decreased
magnitude of flow
Altered seasonal
pattern of flow
Estuarine
response
Reduced
contribution of
catchment
carbon and
nutrients to
productivity
Reduced areal
extent of
flooding and
associated
production
Reduced
estuarine
primary
production
Reduced
habitat
availability and
diversity
Reduced
secondary
productivity of
recreational and
commercial caught
species
Reduced
abundance and
diversity of
estuarine
organisms
Management
effects
Figure 1.3. Mangrove roots exposed at low tide in tidal creek. Photo: B. Pusey. Freshwater inputs stimulate productivity in the estuary and creates more habitat by flooding the coastal saltflats. Future water resource developments (dams and weirs) planned for the southern Gulf region may reduce freshwater inputs. Decreased flows will reduce the amount of material (i.e. sediment, organic carbon and nutrients) needed to sustain primary production in the main channel of the estuary. Decreases in the magnitude of wet season floods will reduce the extent of salt flat inundation, thus reducing habitat diversity and the area available for primary and secondary production. This has flow‐on effects for fish and crustacean species that inhabit the estuary, reducing growth and abundance that in turn reduce catches for commercial and recreational fishers. Aquatic ecosystems in northern Australia Effects on
secondary
productivity
and habitat
Summary effect
Reduced provision of estuarine goods
and services
Figure 1.4. The relationship between water resource development and
estuarine production. Michele Burford (Tropical Rivers and Coastal Knowledge,
Australian Rivers Institute, Griffith University). Chapter 3 ‐ 8
Northern Australia Land and Water Science Review full report October 2009 Box 2: Wasted water? – Fisheries catch information demonstrates otherwise species whose populations also fluctuate in response to
freshwater flows (9). These fodder species are an essential
component of the biodiversity of the estuary and underpin
productive estuarine‐dependent fisheries. These species are
exploited commercially and recreationally, as well as by
indigenous communities. Commercial fisheries in northern
Australia for estuarine‐dependent finfish and shellfish are
worth over $220 million per annum to commercial operators
(14, 15), and supply the hospitality industry with sought‐
after fresh local seafood. There are also major tourism‐
related recreational fisheries for species such as barramundi
and mud crab. In Queensland, an estimated $22M (16) is
spent by recreational fishers targeting barramundi alone
while in the Northern Territory, over $26M is spent annually
on recreational fishing (17), much of which is focused on the
iconic barramundi. The major impact of water resource development on
estuarine fisheries is the creation of physical barriers to
upstream movement, as well as the reduction in sediment
and nutrient loading delivered to the estuary. Water
resource developments can also change the timing, duration
and magnitude of freshwater flowing to estuaries and these
changes impact upon the productivity of estuarine‐
dependent species (11, 12, 13, 18). Ian Halliday and Julie Robins (Tropical Rivers and Coastal
Knowledge, Queensland Department of Primary Industries‐
Fisheries). Water flowing to the ocean is not wasted, but is critical in supporting productive fisheries in estuaries and near‐shore waters (9). In general, the greater the freshwater inflow to estuaries, the greater the fisheries production. Flows can have both immediate and lagged effects on the catchability and abundance of fisheries species. Freshwater flows increase the growth rates of fish and prawns, where faster growth leads to better survival and more individuals in the population. Enhanced growth rates are probably the result of increased food availability that occurs when flows deliver nutrients to the estuary, and enhances its carrying capacity. For species that utilize both estuarine and freshwater reaches of rivers (e.g. barramundi), freshwater flows facilitate fish movement; allowing the downstream movement of mature fish (e.g. for spawning) and the upstream movement young fish that use freshwaters for feeding and growth (Fig. 2.1). This increases the number of fish available for capture, as well as the probability that a fish will encounter a fishing line or net. Cumulatively, these effects generally lead to more fish and prawns available for harvest as flow increases (10, 11, 12). These linkages apply for many estuarine species worldwide (13), but are particularly apparent for estuarine fishery species in northern Australia (11), where wet season flooding is typical. Estuarine‐dependent fisheries species whose populations, and therefore catch, are linked to freshwater flow include banana, tiger and endeavour prawns; barramundi, king threadfin, blue threadfin, grunter, mackerels; sharks; and mud crab. There are also a large number of non‐fished FRESHWATER
ESTUARINE
MARINE
Flows stimulate downstream movement of adults in preparation for spawning
Flows connect perennial
freshwater habitats, enabling
downstream movement of
adults
Reproduction
Movement
Adults spawn at estuary
mouth
Growth & Survival
Some juveniles (~60%) migrate
upstream to freshwater habitats
to mature
Some juveniles (~40%) stay
in estuary to mature
Eggs & larvae
develop in high
salinity water
Flows increase biological productivity
of estuary (i.e. more food available)
Post-larvae & very small juveniles
enter supra-tidal wetland habitats
Flows connect estuary to
perennial freshwater
habitats used by large
juveniles when accessible
Juveniles exit
wetland habitats
Flows connect ephemeral nursery
habitats used by post-larvae and small
juveniles
Recruitment
Flows provide
chemical cues for
larvae to enter the
estuary
Figure 2.1. Conceptual model of the relationship between river flows and barramundi spawning, recruitment and survival. Aquatic ecosystems in northern Australia Chapter 3 ‐ 9
Northern Australia Land and Water Science Review full report October 2009 Hydrological regimes are ultimately dependent on the ambient climate, particularly the seasonal delivery of rainfall and evapotranspiration rates. The average rainfall of northern Australia varies from 3,200 mm.yr‐1 near the coast to less than 1,000 mm.yr‐1 inland (19). Rainfall is strongly seasonal with little falling during the cooler months of May to October, varying greatly from year to year with the strength of the southern monsoon and incidence of tropical cyclones. Cyclones and associated rainfall depressions may deposit huge amounts of water and cause significant flooding. Evapotranspiration rates are very high, resulting in annual deficits (the difference between annual rates of rainfall and evapotranspiration) ranging from almost 1800 mm in the more interior regions, to 600‐999 mm in much of Arnhem Land and Cape York Peninsula and 300‐599 mm in coastal areas (20). As a result of the pattern of rainfall, river flow is also typically highly seasonal with floods occurring during the hot wet months of summer and low flows occurring during the comparatively cooler winter months. Given the importance of flow regime variability for shaping the biophysical attributes and functioning of riverine ecosystems, rivers that share similar hydrological characteristics should therefore also share similarities in their ecological characteristics (21, 22). A recent analysis of the types of riverine flow regimes present throughout Australia (22) identified 12 different and distinct flow regime types varying in seasonality, predictability and intermittency. Six of these flow regime types occur in northern Australia (Fig. 2), of which three are most common: Class 3 – stable summer baseflow; Class 10 – predictable summer highly intermittent; and Class 12 – variable summer extremely intermittent. Six distinct types of flow regimes occur in northern Australia which vary in the extent of seasonality, predictability and permanence (i.e. perennial versus varying degrees of intermittency) Class 3 – Stable summer baseflow
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Figure 2. Flow regime types across northern Australia (based on Kennard et al., 22). The map shows the distribution of the six (of 12) continental flow regime types occurring within northern Australia. Also shown are example hydrographs of daily runoff (ML day‐1 km‐2) for a typical stream gauge in each of the three most common flow regime types. Variation in runoff is shown the long‐term record and for the year and three week period encompassing the flood event with the highest peak magnitude. This figure incorporates data which is © Commonwealth of Australia (23). Aquatic ecosystems in northern Australia Chapter 3 ‐ 10
Northern Australia Land and Water Science Review full report October 2009 The key distinction between these flow regime types is the extent of seasonality, predictability and degree of flow permanence flow during the dry season. Class 3 streams and rivers (stable summer baseflow) are patchily distributed across northern Australia and tend to be associated with groundwater aquifers. They flow all year round as groundwater inputs sustain dry season baseflows. Examples of this flow type include the Daly and Roper Rivers and they are sustained by groundwater primarily derived from the Tindall aquifer (Fig. 3). This flow type also occurs in the Gregory River in the southern Gulf region and the lower reaches of the Mitchell River. Class 10 streams and rivers (predictable summer highly intermittent) are the most common flow regime type present across northern Australia. They are highly intermittent (usually 100‐200 zero flow days per year) and flow predictably occurs during the summer wet but the timing of annual maximum flows is quite variable. This flow regime class is typical of rivers of the Kimberley region (e.g. Fitzroy River), much of the Northern Territory and Cape York Peninsula (e.g. upper reaches of the Mitchell River). Class 12 streams and rivers (variable summer extremely intermittent) rarely flow during the year (> 250 zero flow days per year) and flow is extremely ‘flashy’. Most discharge is associated with single short summer flood events, though their timing and magnitude can vary substantially from year to year. This flow regime type occurs inland on the periphery of the arid zone particularly in the southern parts of the Gulf of Carpentaria region. The degree of flow perenniality and extent of wet season flooding has important implications for the amount of aquatic habitat available during the dry season. Floodplains in particular are ephemeral habitats, filling when the rivers flood and then gradually drying out as the dry season progresses. The extent to which floodplain water bodies dry out completely during the dry season determines the survival of much of the biota (both terrestrial and aquatic) that depend on them. Woinarski et al. (19) suggest that permanent water in stable baseflow streams and rivers (i.e. Class 3) is especially important for the survival of many terrestrial species. The differences in hydrology of these different rivers results in substantial differences in their character and ecology and the ways in which they may respond to flow regime changes. This requires different management approaches which are detailed further below. Rivers with similar flow regimes often share similar ecological characteristics and may respond to human pressures in similar ways. This requires different management approaches for different flow regime types. Aquatic ecosystems in northern Australia Chapter 3 ‐ 11
Northern Australia Land and Water Science Review full report October 2009 Figure 3. A reach of the perennial Daly River, Northern Territory. Photo: M. Douglas. 1.4 THE TYPES OF HYDROSYSTEMS PRESENT IN NORTHERN AUSTRALIA 1.4.1 Estuarine hydrosystems Estuaries form the interface between freshwater and marine ecosystems and are areas of high biodiversity, production and conservation value Estuaries form the interface between freshwater and marine ecosystems and are areas of high biodiversity, production and conservation value. Modern estuaries are relatively new geomorphic features formed by inundation of existing river valleys by Holocene sea level rise (~10,000 years before present). Northern Australian estuaries are numerous and distinguished from those of southern Australia in being tidal dominated rather than wind and wave dominated, tidal range may be as much as 8‐10 m! Estuaries are extremely dynamic landforms (24) due to hydrodynamics of ebb and flood tidal flows yet still retain a strong inherited geological character dependent on the dimensions and geometry of their basins and the amount and nature of sediment delivery from marine and fluvial (riverine) sources. For example, the estuaries of the Prince Regent and Mitchell Rivers in the Kimberley region receive very little fluvially‐derived sediment whilst the Alligator River is completely infilled by both fluvial and marine sediments and the rivers of the Gulf region export fluvial sediments into the Gulf of Carpentaria. These differences impart substantial physical and ecological distinctiveness to the estuaries of different regions (24). Maintenance of natural flow regimes and sediment budgets is critical in maintaining this distinctiveness. Freshwater flows into estuaries are paramount influence on the distribution of sediments: in their absence marine‐derived sediments are not flushed from the system and build up, influencing bar and delta formation, reductions in depth and changes in channel dimensions. For example, pronounced sedimentation and change in structure of the Ord River estuary has occurred as all but the very largest floods have been captured by the Ord River Dam (25). Aquatic ecosystems in northern Australia Chapter 3 ‐ 12
Northern Australia Land and Water Science Review full report October 2009 Natural sediment transport processes are critical to the form and function of rivers, floodplains and estuaries The presence of large and extensive stands of mangrove forest is another feature of northern Australian estuaries (Fig. 4). Mangroves form critical habitat for many species of animal (fish, prawns, crabs (Fig. 5) and birds) especially juvenile forms and are thus important in commercial fisheries (see Boxes 1 and 2) as well as the maintenance of overall biodiversity. Although many mangrove species are salt tolerant, freshwater inputs are crucial to their long‐term survival (26). Extensive supratidal habitats often occur on the landward of the mangrove fringe. These salt flats and salt marshes are typically only inundated by the largest of tides (e.g. floodtides) and even then, the extent of inundation is minimal. However, flooding of these habitats during the wet season combined with high tides may form extensive shallow wetlands which form critical habitat for many species of fish (27), including species of great commercial and recreational value. Salt flats and marshes are also critical for many species of migratory birds (see Box 3) and fish (Box 2). Water flowing to the sea is not wasted: it is critical to the maintenance of biodiversity and productivity of estuaries Figure 4. The estuary of a Kimberley river. Note the fringing mangrove forests and the unvegetated supralittoral salt flats on their landward margin. Photo: B. Pusey. Aquatic ecosystems in northern Australia Chapter 3 ‐ 13
Northern Australia Land and Water Science Review full report October 2009 Figure 5. Mud crabs (Scylla serrata) ready for the pot ‐ a northern delicacy. Photo: A. Pusey. Aquatic ecosystems in northern Australia Chapter 3 ‐ 14
Northern Australia Land and Water Science Review full report October 2009 Box 3: Water birds, wetlands and international avian and human visitors (Fig. 3.3). Waterbirds eat plant material (herbivores), tiny
zooplankton and insects (invertivores), and larger frogs, fish and
reptiles (macrocarnivores). In some wetlands, waterbirds are the
top predator and can influence the local abundance of prey
species (in particular fish populations). They are thus present at
all consumer levels of the aquatic food web. Waterbirds can also
be important prey for crocodiles. Many migrating birds export
carbon generated in northern Australian wetlands to other
regions of Australia and indeed to other parts of the world. Proportion of total
migratory waterbrids (%)
Water birds are a conspicuous component of the fauna of northern Australian aquatic ecosystems (28). Waterbirds are important component of biodiversity and play important roles in ecosystem processes and function. Their presence attracts many domestic and international visitors who come to northern Australia specifically for bird‐watching. An abundant and diverse bird fauna (Fig. 3.1) therefore contributes to northern Australia’s large tourism industry. Of the birds occurring in northern Australia, 145 species are classified as waterbirds (28); almost one fifth of the continental bird diversity! They occur across a variety of habitat types from river channels and wetlands to estuarine and coastal shore environments. 50
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Figure 3.2. The proportion of the total number of migratory waterbirds
listed under EPBC, JAMBA or CAMBA agreements known to breed in
wetlands of northern Australia or that use them as a staging point for
additional migration (28). The extreme seasonality of the northern tropical climate and riverine flow regime means that floodplain and wetland habitats are not available year‐round. As a consequence, many waterbirds migrate seasonally between these and other wetlands in southern Australia and elsewhere around the world. Many such bird species migrate for vast distances between Asia and Australia using the wetlands of the north as either their principal summer habitat or as a staging point for further migration (Fig. 3.2). Many such birds are covered by Australia’s international conservation agreements. For example, Australia is a signatory to two international treaties concerning migratory bird species; the Japan Australia Migratory Bird Treaty (JAMBA) and the China Australia Migratory Bird Treaty (CAMBA). Fifty‐
eight of the 145 northern Australian waterbird species are included in either or both of these agreements. A further six species, including one listed as endangered (the Australian Painted Snipe Rostratula australis) are listed as migratory under the Environment Protection and Biodiversity Conservation Act 1999 (EPBCA). By global standards, northern Australian floodplain wetlands therefore represent a critically important habitat for the long‐term maintenance and viability of waterbirds species. Waterbirds are an extremely important component of the food webs of northern wetlands by virtue of their enormous collective biomass and the diversity of ways in which they gather their food Aquatic ecosystems in northern Australia Number of species
Figure 3.1. Common waterbirds of northern Australian wetlands. a) Black‐necked stork (Ephippiorhyncus asiaticus), b) Australian Pelican (Pelecanus conspicullatus), c) Whistling Duck (Dendrocygna arcuata) and d) cormorants (Phalocrocorax sp.). Photos: B. Pusey. 50
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(28). Water resource development in northern Australia offers both
threats and opportunities for waterbirds. Some species are able
to take advantage of habitat created by impoundments.
Cormorants and other birds able to dive in pursuit of their prey
can take advantage of such habitats whereas many wading birds
and typically non‐diving fish predators such as pelicans cannot.
Birds adapted to highly vegetated shore margins may also do
well in impoundments and the high abundance of the Jacana
(Jacana gallinacea) in Lakes Kununurra and Argyle is one reason
for the RAMSAR listing of these impoundments. Water resource
developments that change the natural flood regime are highly
likely to impact on the many waterbirds that make use of
inundated floodplains for feeding, nesting and rearing their
young. Brad Pusey and Mark Kennard (Tropical Rivers and Coastal Knowledge, Australian Rivers Institute, Griffith University). Chapter 3 ‐ 15
Northern Australia Land and Water Science Review full report October 2009 1.4.2 Riverine hydrosystems The riverine hydrosystem encompasses an extraordinary diversity of habitats and form ranging from tiny headwater creeks, through to large tributary rivers and mighty main channel lowland rivers. The stream networks that form rivers vary greatly in their structure, thus imparting diversity to river form. Rivers may be deeply incised in bedrock or may migrate across their floodplains at times of very high flow, abandoning old channels and creating new habitat (Fig. 6). Streams may be intermittent or perennial depending on the extent to which groundwater contributes to dry season base flows. Isolated pools in intermittent rivers may be sustained by connection to groundwater or hyporheic (subsurface) flow during the dry season and may therefore persist over this period. Others without such connections, depending on their size, may dry up well before the wet season again renews flow. Waterfalls and tufa dams (formed by the precipitation of carbonates at times of low flow) may pose significant barriers to upstream movement by fish and biota but may also form significant habitats (i.e. in the splash zone of the waterfalls or the semi‐lunate pools comprising the tufa dam) and contribute to overall habitat diversity (Fig. 7). Riverine ecosystems support an extraordinary diversity of habitats from tiny headwater creeks, through to large tributaries and mighty lowland rivers Figure 6. The upper Katherine River (left) deeply incised and constrained in the bedrock of the stone country and the lower Coleman River (right) sinuously migrating across its floodplain. Note the abandoned former channels and isolated lagoons (ox bow lakes). Photos: B. Pusey. Aquatic ecosystems in northern Australia Chapter 3 ‐ 16
Northern Australia Land and Water Science Review full report October 2009 Figure 7. The Mitchell River Falls in the Kimberley region (left) and a tufa dam on the lower reaches of the Douglas River in the Daly River catchment. Tufa dams in the Daly River occur most significantly in the Douglas and Flora Rivers of this catchment and collectively form the largest aggregation of this landscape feature in all of Australia. Photos: B. Pusey. Northern Australian contains more than 50 major rivers and many hundreds of smaller streams flowing directly to the sea. These drainages collectively discharge more than two thirds of Australia’s freshwater (19). In addition to differences in flow regime described above, the structure and physical character of northern Australia’s rivers differ from one another, although in many instances there are regional similarities. Figure 8 shows information summarizing three aspects of river structure for rivers grouped into different regions across northern Australia. Northern Australian streams are typified by comparatively low density of streams per unit catchment area (Fig 8a), especially compared to the rivers present to the east of the Great Dividing Range where both rainfall and catchment slope are high (e.g. Wet Tropics region). As one moves eastward, drainage density increases in rivers of the Ord‐Bonaparte, Van Diemen and Arafura regions. It decreases as one moves through the Roper and South‐west Gulf regions and increases again as one moves through the Gulf region and up into Cape York Peninsula. This in part reflects the transition through different belts of annual rainfall (19), but also reflects differences in catchment lithology and slope. Lower catchment slope is characteristic of the wide flat landscape of the Gulf country, consequently these streams have fewer first and second order streams and a greater proportional length of very large rivers (> 6th order). Differences between regions and rivers illustrated in Figure 8a impart diversity in form and thus differences in the structure and distribution of habitat. This, in turn, is important in determining the distribution of biota. Aquatic ecosystems in northern Australia Chapter 3 ‐ 17
Northern Australia Land and Water Science Review full report October 2009 Stream density (km/km2)
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Figure 8. Physical characteristics of river drainage basins across northern Australia (river basins from eastern Cape York ‐2
Peninsula and the Wet Tropics region are included for comparison). a) average stream density (km.km ) for streams of different size. Stream size is indicated by stream order; the smallest streams are first order streams, two of which join to 2
form a second order stream and so on. b) average floodplain area (km ) and floodplain extent (i.e. floodplain area expressed as a proportion (%) of total catchment area). Data are shown individually for the Fitzroy, Daly and Mitchell Rivers (note these rivers were also included in their respective basin groups to the immediate right). Data sourced from Stein et al. (29). Floodplain area and extent also differ across northern Australia, further emphasising the heterogeneity in river character in the region (Figures 8b). The Fitzroy River has a very large floodplain occupying about one third of the total area of its catchment. This is in very stark contrast to other rivers of the Kimberley which typically have a very small floodplain. The Daly River has a floodplain of approximately 12,000 km2 which is a great deal larger than other rivers in its general vicinity. However, when floodplain is scaled by catchment size, it is evident that on a proportional basis, the Daly’s floodplain is comparatively small. The floodplain of the Mitchell River is both large in Aquatic ecosystems in northern Australia Chapter 3 ‐ 18
Northern Australia Land and Water Science Review full report October 2009 area and occupies a much larger proportion of the total catchment area than do other rivers of the Western Cape. Rivers of the Gulf region (Flinders‐Leichardt and South‐east Gulf) have proportionally large floodplains. They are also distinguished by the presence of very large rivers (> 6th order; Fig 8a). Riverine habitats are arranged in a strongly hierarchical manner. Variation in large‐scale environmental features (e.g. climate, catchment topography, geology, and hydrology) influence environmental conditions and aquatic biota at smaller scales (30). For example, a river reach (perhaps many kilometres long) of which there may be many hundred within a large river, may be composed of a series of riffle/pool sequences. Within each riffle or pool, there is variation in depth, water velocity and substrate type. Within each, woody debris, root masses or undercut banks may be found. Collectively these small habitat elements combine to provide physical diversity and distinctiveness to each individual pool or riffle within each reach. Different reaches collectively provide diversity to individual streams and so on. Different habitat types respond differently to changes in flow regime. For example, riffle habitats (shallow fast‐flowing rocky areas) can respond quickly to changes in discharge unlike pools. Riffles contain a different fauna to pools also, and frequently form vital habitat for juvenile fishes that are found in pools as adults. These differences in physical character, coupled with the hydrological differences described above, are likely to result in significant differences in the character, number and importance of different hydrosystems and ecotopes present in each drainage basin and in great ecological differences between hydrosystems and regions. Moreover, these differences emphasise that relationships between hydrology, geomorphology and ecology can be variable in space. It is a mistake to think that all northern Australian rivers are the same and that they will respond in the same manner to particular types of disturbance such as water resource development or widespread changes in land use. 1.4.3 Lacustrine (lake) hydrosystems Natural lakes other than those associated with channel migration are not a significant hydrosystem in northern Australia. There are no lakes formed by glaciers, tectonic movement or volcanism, for example. Although outside of the geographic scope of this report, volcanic lakes are present in the Wet Tropics of north eastern Australia and profuse aggregations of lakes formed by aeolian processes (wind) are present in the dune fields of Shelbourne Bay and Cape Flattery of eastern Cape York Peninsula (31). Oxbow lakes (Fig. 9), on the other hand, are often a very common feature in river floodplains of northern Australia. Ox bows (referred to as billabongs in southern Australia and most frequently as lagoons in northern Australia) are formed when a meandering river channel becomes so sinuous as to join back upon itself and “pinch off” of a segment of the meander loop. This section then becomes isolated as the channel migrates away with time. Such lakes retain much of their riverine character and much of its former fauna and flora not specifically requiring flowing water habitats. Although often quite deep soon after formation, oxbow lakes progressively become shallower with time as organic matter and sediment is deposited in floods and as in‐situ plant production develops along their margins. Oxbow lakes are important in the floodplain environment as they frequently form permanent aquatic habitats and thus provide refuge for aquatic organisms when other, shallower, floodplain wetlands dry out. Aquatic ecosystems in northern Australia Chapter 3 ‐ 19
Northern Australia Land and Water Science Review full report October 2009 Figure 9. Sunset at Mission Hole, a large oxbow lake on the lower Daly River floodplain. Photo: B. Pusey. 1.4.4 Palustrine (floodplain) hydrosystems Floodplains are a major component of the aquatic landscape across northern Australia and may comprise over a third of the total catchment area of many rivers, and even more in the rivers of the Gulf Region (Fig. 8d). Floodplains are a vital component of riverine ecosystems. As the name suggests, the presence of water on floodplains is largely determined by seasonal flooding derived from either from local rainfall as well as river channels during periods of overbank flow in the wet season. As water spills out over the river levee banks, it immediately slows and spreads out to form vast shallow palustrine wetlands (Fig. 10). Sediment and attached nutrients settle out and water clarity increases, which when combined with high water temperatures typical of summer, provides perfect conditions for high primary production. Production on floodplains is an integral component of the food webs of riverine landscapes. Floodplains provide habitat during the wet season for an enormous diversity of animals such as frogs, fish and turtles in addition to many species of plants. Northern floodplains also support very high numbers and diversity of waterbirds, many of which migrate between northern Australia and other parts of the world (see Boxes 3 and 4). Shallow, warm, nutrient‐rich floodplains are among the most productive ecosystems in the world. They provide perfect habitat for frogs, fish, turtles and waterbirds and tie up huge amounts of carbon Aquatic ecosystems in northern Australia Chapter 3 ‐ 20
Northern Australia Land and Water Science Review full report October 2009 Figure 10. A vast shallow floodplain wetland on the lower Daly River in the early dry season. Photo: B. Pusey. Floodplains are among the most productive systems in the world contributing enormously to the energy and carbon budgets of the riverine systems with which they are associated (34, 35). Summarising decades of research undertaken on the Magela Creek system in Kakadu National Park, Pettit et al. (36) estimated that annual floodplain primary production of carbon (C) was comprised of 2500 to 5500 kg C. ha‐1 of aquatic grasses and 850 kg C ha‐1 of epiphytic algae. Production of primary consumer organisms (aquatic invertebrates) was 6 – 60 kg C ha‐1. These very high production values supported high biomass of secondary consumer organisms; between 11 and 45 kg ha‐1 dry weight of freshwater fish, 3.2 kg ha‐1 of turtles, 1.12 – 3.40 kg ha‐1 of waterbirds (during wet season, much higher during the dry season) and 0.8 – 2.5 kg ha‐1 dry weight of non‐hatchling crocodiles (see Box 5). Clearly, floodplains produce and support a large amount of biomass. Many floodplain waterbodies do not persist through the dry season; at best they are greatly reduced in size. Whilst this may result in the senescence of much biomass generated during the wet season, it provides a bountiful harvest for many waterbird species and terrestrial fauna that feed upon fish and frogs. It also provides very important opportunity for the cattle grazing industry. Grass production during the wet season provides forage for cattle throughout the long dry. Aquatic ecosystems in northern Australia Chapter 3 ‐ 21
Northern Australia Land and Water Science Review full report October 2009 Box 4: Magpie geese – icons of the north
The magpie goose (Anseranas semipalmata) is an iconic wildlife species with significant socio‐economic values; it is a totemic animal for Aboriginal people and their eggs and meat are important sources of bush tucker. Magpie geese are also an important game waterfowl species for non‐
Indigenous hunters, and are part and parcel of ecotourism in the north. The magpie goose, sole member of the family Anseranatidae, is found only in Australia and the southern lowlands of West Papua and Papua New Guinea. They are widespread and abundant across the coastal floodplains of northern Australia, with the Northern Territory (NT) supporting the world’s largest population, major nesting areas and dry season refuges. Kakadu National Park is home to about 70% of the NT goose population in the late dry season because it contains the most extensive stands of water chestnut sedge (Eleocharis dulcis) in northern Australia, a preferred food. Magpie geese were once common in south‐eastern Australia before the 1900s but are now rarely seen in the south due primarily to a loss of wetland habitat. Small resident populations still occur in tropical northern Queensland and Western Australia. Their life cycle is inextricably linked to seasonal river‐
floodplain dynamics and a dependence on food availability during the dry season food source. A conceptual model of the life history and ecology of magpie geese in relation to seasonal rainfall and river‐floodplain dynamics is illustrated in Figure 4.1. Inundation of the large floodplains of the far north is determined by the summer monsoon onset, duration, and intensity. River flow is strongly correlated to rainfall in catchments, which in turn determines river stage height (Fig 4.1, top LH graph), and the extent and period of inundation of floodplains. Flooding triggers dramatic changes in the composition and biomass of floodplain vegetation and, hence, the availability of magpie goose nesting habitat and food. Tropical floodplains are dominated by wild rice (Oryza spp.) grasslands and tall sedges such as the water chestnut. Geese aggregate in large breeding colonies on wetlands that offer both abundant nest sites and a supply of food for the young and adults. The seeds of wild rice are a key food source for emergent goslings and adults in the late wet season. Unseasonal extreme flooding in one year may however result in low numbers of magpie geese in subsequent years. If such flooding occurs after nests are constructed and eggs lain, it can result in nest inundation or dislodgement and loss of that year’s fledglings. As the Aquatic ecosystems in northern Australia wetlands begin to dry out, geese move to swamps that
have extensive stands of water chestnuts. During the dry
season they shuffle through the sticky mud, digging up the
starchy tubers with their hooked bills and gorging on this
high energy food (32, Fig. 1). As the wetlands continue to
dry out geese congregate in increasing numbers on the
remaining swamps. The late dry season is a lean period
until the next rains when the seasonal cycle is repeated. Just as fascinating as the link between the annual wetting
and drying cycle and the life history of magpie geese is the
discovery that their populations may exhibit decadal trends
in population size that are coupled to similar trends in
mean long‐term river flow (Fig. 4.1). The bottom LH graph
shows 20‐25‐year decadal trends in discharge (ML) of five
major NT streams using a statistic called cusum that teases
out underlying trends from noisy data. The bottom RH
graph shows the concordant trend in magpie goose
numbers meaning that wetter years result in higher
magpie geese numbers (12, 33). This effect is mediated via
improved rearing success during the breeding season and
better survival of adults and fledglings during the lean dry
season. Annual rainfall, and ultimately river flow, therefore
drives the spatial and temporal dynamics of magpie geese
at regional and decadal time scales through its direct
influence on floodplain vegetation dynamics. Magpie goose habitats are vulnerable to multiple threats
including invasive species and climate change. Pigs are an
aggressive predator of geese nests. Aggressive aquatic
weeds such as mimosa (Mimosa pigra), para grass
(Urochloa mutica) and olive hymenachne (Hymenachne
amplexicaulis) are increasingly threatening floodplain
wetland habitat integrity. Mimosa has already colonised
over 1,400 km2 of NT coastal floodplains, suggesting that
annual nest production may halve (12). This may explain
low observed nest numbers since 1999 (32) despite several
years of above average rainfall and river flow. Mimosa now
threatens the very survival of magpie geese in the NT
because without wetland habitat they cannot exist, as
demonstrated clearly by the disappearance of south‐
eastern Australian populations in the last century. Magpie
geese in the NT are vulnerable to predicted sea level rises
because about 70% of their population uses dry season
habitat that is less than 1m above current sea level. Any
potential water resource development that impacts on
flooding regime or wetland persistence is highly likely to
impact on this iconic bird. Peter Bayliss (Tropical Rivers and Coastal Knowledge,
CSIRO Marine & Atmospheric Research).
Chapter 3 ‐ 22
Northern Australia Land and Water Science Review full report October 2009 Box 4: Magpie geese – icons of the north Figure 4.1. Conceptual model of the ecology of magpie geese in relation to seasonal and decadal trends in river‐floodplain dynamics in the NT. Top LH graph shows the tight relationship between Katherine River flow volume (ML), stage height (m) and river water level (m) that triggers bank overflow and floodplain inundation, typical of NT streams and rivers. Bottom LH graphs show 20‐25 year decadal trends in fiver major NT streams and the corresponding 20 year period trend in magpie goose numbers. Nest photo by P. Whitehead, others freely available on the Internet.
Aquatic ecosystems in northern Australia Chapter 3 ‐ 23
Northern Australia Land and Water Science Review full report October 2009 Box 5: Rivers and reptiles Two species of crocodile, the freshwater crocodile (Crocodylus johnstoni) and the larger estuarine crocodile (Crocodylus porosus) occur in northern Australia. Turtles and crocodiles show a variety of adaptations to the tropical hydrologic regime. For example, the estuarine crocodile breeds over the wet season, laying its eggs in a mound of vegetation, whereas the freshwater crocodile breeds during the late dry season, laying its eggs in exposed sand banks (37). Nest site selection is very specific in estuarine crocodiles; nests are rarely located more than a 100 m from permanent water (38). Inundation of these nest sites by abnormal late wet season flooding or abnormally high tides is a major source of mortality for nestlings during the wet season. Similarly, unseasonal inundation of river sand banks during the dry season results in the high levels of mortality in freshwater crocodiles. Sand bank nesting sites are frequently in short supply in many northern rivers and permanent or temporary loss of this habitat can have significant effects on population size. Figure 5.1. The estuarine crocodile (Crocodylus porosus) (top) and the freshwater crocodile (Crocodylus johnstoni) of northern Australia. Photos: B. Pusey (top), D. Wilson (bottom). In intermittent rivers, little feeding occurs during the dry season, especially for freshwater crocodiles which may attain very high densities in isolated waterholes during this period. Both species use the wet season to disperse into new habitats and are heavily reliant on food gained during this period for growth and accumulation of resources for later reproduction (37). Both species are top or apex predators, thus the maintenance of riverine production during the wet season is critical for their survival and the integrity of aquatic food webs. Tropical Australia is home to 15 species of turtle (12 of which occur in the area here defined as northern Australia), although many subspecies are recognised and greater specific diversity may be present (39). Unlike the widely distributed crocodiles, several turtles are restricted to only a few river basins (Fig. 5.2). The Leichardt, Alligator, Fitzroy and especially the Daly Rivers are notable in this regard, with the latter containing the core Aquatic ecosystems in northern Australia population of the rare pig‐nosed turtle (Carettochelys insulpta) (Fig. 5.3). High
Relative
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Figure 5.2. Relative endemism in the freshwater turtles of northern Australia. River basins with darker shading have a comparatively higher number of species with restricted distributions (Data sourced from Georges and Merrin, 39). Like the freshwater crocodile, pig‐nosed turtles nest on exposed sand banks within 5m of the water’s edge during the dry season (40). Hatchlings emerge from their eggs, if fully developed, upon inundation by the first summer freshes or heavy monsoonal rain. Unseasonal inundation results in death. Figure 5.3. The pig‐nosed turtle (Carettochelys insculpta). Photo: D. Wilson. In contrast, the widely distributed northern snake‐neck turtle (Chelodina rugosa), which is common in wetland and floodplain habitats, lays its eggs in water during the late wet and early dry seasons. This species can lay dormant (aestivate) deep in the mud during the dry season but substantial mortality may occur during this period especially when the dry season is prolonged. Snake‐necked turtles are culturally significant species for many Aboriginal people. Brad Pusey and Mark Kennard (Tropical Rivers and Coastal Knowledge, Australian Rivers Institute, Griffith University). Chapter 3 ‐ 24
Northern Australia Land and Water Science Review full report October 2009 1.4.5 Subterranean (groundwater) hydrosystems Subterranean hydrosystems occur under ground and are usually, but not always, associated with groundwater aquifers. This hydrosystem also includes the hyporheic zone, the saturated soil interface between the river, land and groundwater. Subterranean hydrosystems have been little studied in northern Australia but early indications are that they contain an extremely diverse and important fauna with many endemic species (see Box 6) and it is only recently that the integrity of these systems has received attention. The long‐term sustainability of subterranean hydrosystems is intimately linked to the maintenance of groundwater (excepting those circumstances where the subterranean system is impervious and relies on capturing surface runoff). Recent research in Australia (summarised in Humphreys, 41) suggests that many subterranean organisms occur in small and very patchily distributed populations, making them vulnerable to disturbance with little chance of recovery. The best known subterranean fauna occur in the mineraliferous regions of north‐
western Western Australia but it is likely that many regions of northern Australia with large groundwater aquifers (such as those that underlay the Daly, Roper and Gregory Rivers) also contain diverse and unique subterranean communities. Petheram and Bristow (20) noted that the maintenance of ecological values associated with groundwater will be very challenging in the more arid parts of northern Australia where aquifer recharge areas need to be several orders of magnitude larger than the area being irrigated by water drawn from underground aquifers. Subterranean ecosystems have been little studied in northern Australia but appear to contain an extremely diverse and unique array of aquatic animals 1.4.6 Artificial hydrosystems The most conspicuous artificial hydrosystems present in northern Australia are the impounded waters of the 27 large dams that occur across the landscape (see Box 7). Two of these, the impoundments of the Ord River (Lakes Argyle and Kununurra) are declared RAMSAR sites (see Box 8). There is also numerous smaller artificial water bodies such as farm dams and drainage channels used to deliver water from impoundment to irrigation areas or between rivers (i.e. interbasin transfer systems). Of the latter, the only such system of note is that associated with the Mareeba Dimbullah Irrigation Scheme which connects the eastern flowing Barron River systems to the headwaters of the Mitchell River. Serious concern has been expressed about the potential for this scheme to enable the transfer of distinctive genetic stocks of native fish as well as alien fish species from the Barron River. Foremost among such concerns is movement of the alien cichlid tilapia (Oreochromis mossambicus), a declared Noxious species (46). Tilapia can eat a variety of small native fishes (even juvenile barramundi) and pose a special threat to communities in isolated waterholes (47). Tilapia can also tolerate seawater and could thus move to river systems throughout the Gulf region if they were to make their way down the Mitchell River. Sewage treatment ponds (Fig. 11) are also common smaller artificial hydrosystems in northern Australia and pose a potential threat if effluent released to rivers contains high levels of nutrients, of if they become inundated by flood flows. Artificial hydrosystems also provide provides ideal habitat for growth of aquatic weeds and other invasive aquatic pests. The disruption caused by artificial hydrosystems creates perfect conditions for invasive plants and animals to prosper Aquatic ecosystems in northern Australia Chapter 3 ‐ 25
Northern Australia Land and Water Science Review full report October 2009 Figure 11. Sewage treatment ponds at Katherine adjacent to the Katherine River. Note how closely it is situated to the Katherine River in the foreground. Photo: B. Pusey. Aquatic ecosystems in northern Australia Chapter 3 ‐ 26
Northern Australia Land and Water Science Review full report October 2009 Box 6: Groundwater fauna – unseen biodiversity and role in aquatic ecosystems
Recently, groundwater ecosystems have been recognised to contain globally important biodiversity and consequently ecosystem function (42, 43). Over the last decade Australia has been shown to be a global hotspot for subterranean biodiversity in both terrestrial (troglofauna) and aquatic (stygofauna) habitats (41, 44). This knowledge largely pertains to north‐western Australia (the Pilbara and Yilgarn regions and the Carnarvon Basin), but significant knowledge is emerging of diverse stygofaunas from other regions of the continent, particularly the Kimberley and Northern Territory. As elsewhere, the subterranean fauna was initially reported from carbonate karst areas (a landscape formed by the dissolution of soluble rocks, including limestone and dolomite) but more recently has been found to inhabit voids in pseudokarst (typically in sandstone, lava or laterite), alluvial aquifers, lacustrine and groundwater calcretes, pisolites, fractured rock and basalts. Stygofauna may be expected to occur wherever water‐filled voids occur (41). These factors, combined with the geomorphological stability of the shield regions and ancient origins (i.e. predating the fragmentation of Gondwana), may account for Australia having arguably the most phylogenetically diverse stygofauna globally. Lacking light, subterranean ecosystems typically lack primary production and depend on imported organic matter as an energy resource, mostly in the form of dissolved organic carbon. Typically, stygofauna possess a suite of convergent traits associated with adaptation to subterranean life, such as reduction or absence of eyes, pigment and hardened body parts, reduced metabolic rate, and a range of behavioural and life history traits (i.e. typically longer lived and having smaller broods than surface counterparts) (Figs. 6.1. and 6.2). These life history traits and typically patchy discontinuous distributions may make stygofauna particularly vulnerable to perturbation and slow or unable to recover. Stygofauna may be relatively young of origin, such as the
world’s most diverse fauna of subterranean diving beetles
driven underground in the late Tertiary by the onset of
aridity, or else much older and widely vicariant, comprising
genera otherwise known from caves on either side of the
North Atlantic, such as the anchialine fauna bordering the
North West Shelf (41). The Kimberley and the Western Shield
contain stygobitic isopod lineages predating the
fragmentation of Gondwana (45). Figure 6.2. Milyeringa veritas, an endemic genus of blind cave fish
(Family Eleotridae) from Cape Range. Photo: D. Elford. Kimberley stygofaunas are known from alluvial deposits in
the Ord drainage both at Argyle Diamonds Mine and in the
Ord Irrigation Area, in sandstones of the Pentacost Range, on
Koolan Island, and widely within the Devonian fossil reefs of
both the east and west Kimberley. In the Northern Territory,
stygofauna are known from Katherine, Ngalia Basin and the
Gulf Country, and from Lawn Hill in Queensland. The
discovery of a new species of cave fish on Barrow Island in
2009, representing a 50% increase in the number of species
of stygobitic fish in Australia, is indicative of the poor state of
knowledge of subterranean fauna even in highly developed
areas. The fate of northern Australia’s stygofauna is intimately
linked to the condition of its groundwater. Over‐exploitation
of aquifers may lower groundwater levels sufficiently to
desiccate subterranean habitats and cause extinction.
Pollution of groundwaters is also potentially able to
eliminate stygofauna. Maintenance of subterranean fauns is
only recently receiving due attention (e.g. Katherine River
Water Resource Plan) despite the fact that Australia may
host more than 20% of the world’s stygofauna! William Humphreys (Western Australian Museum). Figure 6.1. Norcapensis mandubulis, a genus of subterranean amphipod (Family Melitidae) endemic to Cape Range, North West Cape peninsula. Photo: W. Humphreys. Aquatic ecosystems in northern Australia Chapter 3 ‐ 27
Northern Australia Land and Water Science Review full report October 2009 Box 7: Going against the flow – dams in northern Australia
Water resource development (i.e. dams, weirs, tidal barrages) and other human activities can change natural riverine flow regimes, cause longitudinal barriers to movement of biota, as well as a host of other impacts on aquatic ecosystems. Most of the rivers of northern Australia have been minimally affected by water resource development, notwithstanding isolated riparian extraction and stock watering (48). In addition, the vast majority of rivers run freely (i.e. relatively few barriers), in stark contrast to the case in southern Australia (49). However, some rivers and streams have been impounded. There are 27 impoundments with a capacity above 0.2 GL (Fig. 7.1a) in the region, with the majority of these being located in Queensland (mostly on the upper Mitchell and Leichardt Rivers). This contrasts markedly with the 467 dams constructed on rivers in the remainder of Australia (50). (a)
6
4
8
6
2
4
2
19
80
s
19
70
s
State
19
60
s
WA
19
50
s
NT
19
40
s
QLD
19
30
s
0
0
Decade
12
(c)
10
10
(d)
8
8
6
6
00
0
<1
0
00
0
<1
<1
00
tio
n
ga
Irri
n
ati
o
cre
Re
n/I
rrig
a
ati
o
Ur
ba
Ur
ba
n
/Re
cre
Ur
Wa
s te
0
n
2
0
tio
n
2
<1
0
4
4
ba
n
Number of dams
(b)
10
<1
Number of dams
12
Capacity (GL)
Purpose
Figure 7.1. Characteristics of dams in northern Australia. Number of dams in a) each state; b) constructed in each decade since 1930; c) in each major use class; and d) in different classes of reservoir capacity (in GL). Note that the dams less than 0.2 GL are not included (data sourced from ANCOLD Inc., 50). Dams and weirs were constructed in northern Australia to supply water for irrigation or urban water supply, although some such impoundments have dual purposes (additional recreational and irrigation needs) (Fig 7.1c). Most were constructed more than 40 years ago with no new major impoundments being constructed in the last two decades Aquatic ecosystems in northern Australia (Fig. 7.1b). Impoundments in northern Australia are typically less than 100 GL in capacity with only one large impoundment (> 10,000 GL) located in the Ord River basin
(Fig. 7.1d). The structure and function of riverine ecosystems, and the adaptations of their constituent freshwater and riparian species, are determined by natural patterns of variation in river flows (4). Small dams can modify natural riverine flow regimes by impounding smaller floods and any residual flow that may occur during the late wet season and throughout the dry season. By virtue of their larger storage capacity, large dams have the capacity to substantially modify wet season flow regimes by trapping all but the larger floods. This has the potential to greatly alter river‐floodplain inundation regimes. Inundation of floodplain wetlands during flooding is critical for wetland health. Northern Australia contains the largest area of unmodified wetlands in Australia (24); the maintenance of these wetlands in critical for maintaining the biodiversity of northern Australia. Changes to natural dry season flow regimes can also occur downstream of dams. For example, impounding natural dry season flows in perennial rivers
can reduce water levels downstream and affect aquatic habitat availability and connectivity. In contrast, dry season flow releases (e.g. for irrigation supplies) can artificially elevate naturally low river flows. These hydrologic changes can have major impacts on aquatic ecosystems downstream. Northern Australian impoundments have been shown to be reservoirs of weed species, providing a source of colonists for areas downstream (51, 52, 53). Degraded water quality and the proliferation of blue green algae in northern reservoirs has also been reported (54). Change in riverine habitat from running water to still water
conditions within impounded area may cause a change in native species composition to favour those species capable of utilising deep still water habitats for reproduction, foraging and refuge (e.g. alien fish species such as tilapia or native species such as bony bream, fork‐tailed catfish).
Dams and weirs form effective barriers to movement for migratory species of fish and crustaceans such as the freshwater prawn (Macrobrachium spp). Brad Pusey and Mark Kennard (Tropical Rivers and Coastal Knowledge, Australian Rivers Institute, Griffith University). Chapter 3 ‐ 28
Northern Australia Land and Water Science Review full report October 2009 Box 8: The Ord River – a cautionary tale
The Ord River in the Kimberley Region offers a telling example of the many changes in river character and ecology that occur with the construction of a large impoundment and development of irrigated agriculture. The Ord River Irrigation Plan was initiated in the early 1960s with the construction of the Kununurra Diversion Dam (KDD) followed by the Ord River Dam (ORD) in 1973. The KDD is a 20 m high structure with a capacity of 101 GL whereas the ORD is much larger, with a total capacity of 5,800 GL. Capacity is more than twice the mean annual flow of the river system. More than 11,000 ha (Ivanhoe Plain and Packsaddle Plain) is irrigated by the scheme and private sector interest in developing a further 7,000 – 16,600 h was sought by the Western Australian government in 2006 (55). The changes in the flow regime of the river have been profound. Prior to construction, flow was naturally intermittent and highly variable, with over 80% of the annual flow occurring between January and March in a series of short (7‐10 day) floods. During the dry season, flow ceased altogether and the lower river became a series of isolated deep pools. Following construction, mean annual flow below the dam decreased by 35%, wet season flows decreased by 67% with all but the very largest of floods being trapped above the dam. In contrast, dry season flows were increased by 439%. This seasonally intermittent river had been changed to a perennial one, primarily to deliver water downstream for irrigation. Major changes in river character have now occurred both upstream and downstream of the dams. Migratory fish, especially species like barramundi that must have access to the estuary to breed are now prohibited from accessing much of the river’s length because of the barrier imposed by the Kununurra Diversion Dam. Many kilometres of river upstream of the dam has been inundated, changing formerly meandering river channels interspersed with shallow fast‐flowing areas to a large, homogenous deep lake (Lake Argyle). This has caused a major change in species composition and ecology in this part of the river (55) Downstream of the ORD, major physical and ecological changes have also occurred. These include accumulation of aquatic plants in the stream channel (55) and growth of dense thickets of vegetation along the river’s margins (56), with a consequent narrowing of the river channel (57). Changes in species composition of the riparian vegetation occurred because of a reduction in the flood disturbance regime (58). Changes in riverine sediment transport dynamics have been profound, with consequent changes to channel morphology and habitat integrity. Major increases in the delivery of marine sediments into the river by extreme tides has occurred. This sediment is no longer flushed out of the system due to the reduction in the magnitude and frequency of floods (57). Sediment delivery from further upstream has been reduced as it is now largely trapped in Lake Argyle. This, together with the absence of flood flows, has resulted in a reduction of Aquatic ecosystems in northern Australia delivery of sediment and nutrients to the floodplain wetlands and the extent to which these important habitats are inundated. The application of fertilisers, pesticides and herbicides (biocides) on irrigated crops has resulted in these chemicals being delivered to the river ecosystem. A mass balance model developed for Ivanhoe Plain revealed significant loss of nutrients from crop lands (Fig 8.1) with attendant risks of weed proliferation and change to the aquatic food web downstream. 447 GL
Ivanhoe Plain
Nitrogen - ~16 fold increase
Phosphorus - ~4.5 fold increase
190 GL
Figure 8.1. Estimated mass balance model for nitrogen and phosphorus in irrigation water return to the Ord River after application to crops on Ivanhoe Plain. Data sourced from Lund and McCrea (59). Residues of biocides such as Endosulphan have been detected downstream of the irrigation areas and have been implicated in fish kills in the Durham River (59). Crops such as sugar cane and cotton often use a wide variety of biocides (up to 17 different chemicals) in other parts of Australia (60). Some of these have the potential to remain in the ecosystem for an extended time. For example, 435 tonnes of DDT and 412 Toxaphene were applied in the scheme area between 1964‐1974 in a fruitless attempt to control the Heleothis moth. Despite ceasing three decades ago, residues of these compounds are still detectable in animals such as freshwater and estuarine crocodiles at concentrations as high as any reported in the world (61). Brad Pusey and Mark Kennard (Tropical Rivers and Coastal Knowledge, Australian Rivers Institute, Griffith University). Chapter 3 ‐ 29
Northern Australia Land and Water Science Review full report October 2009 1.4.7 Riparian zones The riparian zone is the narrow strip of vegetation that grows along a river’s banks (see Boxes 9, 10 and 11). Riparian zones are not specifically included in the classification scheme presented in Table 1 yet are a vital component of the riverine landscape. In the wet‐dry tropics, they are comprised of specifically adapted flora not usually found in the surrounding savanna country, typically having high water requirements. For example, the riparian zone of the lower Daly River is northern Australia’s largest contiguous area of gallery rainforest (62). Elsewhere, monsoonal rainforest is restricted to a mosaic of very small fragments. The riparian zones of northern Australian rivers are unusually narrow compared to elsewhere in Australia because of the intense water stress that develops in terrestrial areas during the dry season. Unusually high biodiversity and biological activity are characteristic of riparian zones and they are very important to aquatic ecosystems (68, 69). Terrestrial primary production derived from the riparian zone and floodplains is acknowledged as a vital source of energy in riverine food webs (70). Other important influences include thermal buffering, the provision of shade and its influence on in‐
stream primary production, nutrient interception, storage and release, enhancement of bank stability, the provision of coarse woody material as habitat and substrate for fish, invertebrates and microalgae, mediation of changes in channel morphology and habitat diversity and refuge from disturbance at a variety of scales from that of the particle (i.e. individual pieces of wood) to that of the watershed (see Pusey and Arthington, 66). Riparian zones support unusually high biodiversity and biological productivity but are particularly sensitive to changes in surface water and groundwater regimes The structure and nature of riparian zones is highly dependent on the natural flow regime. The size and types of trees in tropical riparian zones is largely governed by the annual flooding regime whereas survival over the dry season, when water requirements of the riparian vegetation remain high, is highly dependent on the continued presence of water in the channel in the case of riparian zones on perennial streams, or the presence of, and access to, groundwater, in the case of riparian zones along intermittent streams (58). Prolonged reductions in water availability during the dry season can result in tree death and consequent changes in terrestrial and in‐channel erosion rates. Aquatic ecosystems in northern Australia Chapter 3 ‐ 30
Northern Australia Land and Water Science Review full report October 2009 Box 9: Food webs – who’s eating what?
Food webs describe the feeding relationships and the flow of energy throughout the ecosystem. Food webs generally start with primary producer organisms (e.g. plants and algae), which are then eaten by primary consumers animals which are in turn eaten by secondary and higher order consumers (predators). Energy flow can be a simple food chain from primary producer to primary consumers to higher order consumers but more often is more complex and the term food web is a more appropriate description of this energy pathway. For example, food webs often contain omnivores which consume both primary and secondary production. Freshwater food webs are predominantly based on a combination of energy sources from within the water body (autochthonous) and subsidies from riparian and terrestrial (allochthonous) sources. Algae tend to form a more important source of carbon in aquatic food webs compared to other primary producers (e.g. aquatic macrophytes). However, other sources of carbon derived from the terrestrial environment may become significant at certain times of the year. For example, during the wet season, when high flows can increase turbidity thereby decreasing light penetration and primary production, terrestrial vegetation, insects and even vertebrates inundated by floodwaters become an important food source for some species (see Box 11). During the dry season when river flows are low or when pools become isolated and contract in size, terrestrial inputs of tree seeds, fruits and insects may become a very important food source for some species. Non‐aquatic consumers such as waterbirds, riparian birds and snakes may add additional complexity to aquatic food webs (Fig. 9.1). Water
birds
Riparian
birds
Riparian
trees
Riparian
invertebrates
Crocodiles
Emergent
plants
Archerfish
Barramundi
Epiphytic
algae
Rainbowfish
Bony
bream
Benthic
invertebrates
Detritus
Benthic
algae
Terrestrial
producer
Aquatic
producer
Source
Aquatic
consumer
Terrestrial
consumer
Figure 9.1. Conceptual diagram of a possible food web in a northern Australian river. Arrows represent pathways of organic material and energy. Major food sources are denoted by the broken lines around each food source. Not all possible pathways are presented. Aquatic ecosystems in northern Australia Hydrological connectivity facilitates the movement of
organic material and biota and this is critical for maintaining
food web dynamics and ecosystem function at a range of
spatial scales. In addition to small‐scale lateral transfers
between a river and its riparian zone (Fig. 9.1), larger scale
lateral transfers between the river and its floodplain also
occur during the wet season. Given the enormous
comparative differences in area (floodplains vs river), the
transfer of material and energy between these two habitats
may be enormously important for river function and
ecological integrity. Longitudinal fluxes of organic material are also a distinctive
feature of riverine food webs, with fluxes occurring between
headwater streams, main channel reaches and even
estuaries and the near‐shore marine environment. This
movement may be passive (i.e. algae, detritus and
invertebrates are moved downstream in the flow) or active,
involving the upstream and downstream migrations of fish
and invertebrates such as freshwater prawns. Seasonal
differences between the wet and dry seasons have a large
influence on the distribution and productivity of biota within
the river as well as connectivity with the adjoining floodplain
and the waterholes within the floodplain. This strong
interconnection of aquatic habitats highlights the
dependence of food webs on the river flow regime and the
critical role played by the strong seasonality in tropical
Australian rivers. Douglas et al. (63) proposed five general principles to
characterise the food webs and ecosystems processes in
northern Australia. These are: (1) seasonal hydrology is a
strong driver of ecosystem processes and food web
structure; (2) hydrological connectivity is important for
terrestrial‐aquatic food web subsidies; (3) river and wetland
food webs are strongly dependent on algal production; (4) a
few common macroconsumer species have a strong
influence on benthic food webs; and (5) omnivory is
widespread and food chains are short (i.e. there are only a
few levels to the food web) These principles highlight the links between different parts
of the riverine environment and the overriding influence of
the natural flow regime. Food webs are the basis of natural
communities and the best way to maintain that base is to
protect the natural flow regime and connectivity. Neil Pettit (Tropical Rivers and Coastal Knowledge,
University of Western Australia). Chapter 3 ‐ 31
Northern Australia Land and Water Science Review full report October 2009 Box 10: Riparian zones – sustaining the rich bird fauna of the north
The riparian zones of northern Australian rivers and streams support a rich bird fauna. Both the diversity of species and the total abundance of birds are far greater in this habitat than in neighbouring (terrestrial) landscapes. For example, bird biodiversity surveys in the wet‐dry tropics of Northern Territory’s Top End (64) reveal that total bird diversity was much greater in riparian zones (167 species) than in surrounding non‐riparian habitats (81 species). The number of species recorded only in the riparian zone was over three times the number recorded only in the savanna (Fig. 10.1). In another example, within a 200 m stretch of the Mary River in the Fitzroy catchment of Western Australia’s Kimberley region, a morning survey revealed over 300 individual birds from 33 species utilising the riparian zone; much greater diversity and bird abundance than observed in adjacent area of similar size (P. Kyne, unpublished). Matched Savanna
+ Riparian zone
80
Raptors
& other
carnivores
Raptors
& other
carnivores
Nectarivores
Nectarivores
60
Insectivores
Insectivores
40
Granivores
20
Granivores
Frugivores
Frugivores
Aquatic
carnivores
Aquatic
carnivores
0
Daly River
Catchment
Fitzroy River
Catchment
Figure 10.2. Proportional contribution (%) of different feeding
groups to the total species richness in riparian zones of the Fitzroy
and Daly Rivers (P. Kyne, unpublished). Riparian zone
Habitat
100
Savanna
Riparian
zone only
Number of species
180
160
140
120
100
80
60
40
0
20
Savanna
only
Figure 10.1 Bird species richness in adjacent savanna and riparian zone habitats (data sourced from Woinarski et al., 64). Matched savanna + riparian zones refers to pooled samples in adjacent site locations. Riparian zones provide critical habitat and resources for birds in terms of feeding, refuge, watering, nesting and rearing. For example, the broad array of food resources available in the riparian zone is reflected in the comparatively high number of bird feeding groups represented in these areas. Data from surveys in the Daly River catchment of the NT and the Fitzroy River catchment of WA reveal that the proportion of species within these feeding groups is similar between catchments (Fig. 10.2). The bird species occurring in riparian zones are also divisible into two broad groups: those feeding within its habitats, and those visiting to drink and/or bathe. The latter group are those that primarily feed elsewhere (in particular the surrounding woodland or grassland) but require regular access to water. A large proportion of these are the granivores (the seed eaters); an example is the Endangered Gouldian Finch. Aquatic ecosystems in northern Australia Birds are an integral part of river ecology, occupying high
trophic levels in relatively short aquatic food webs (see Box
9). Some aquatic predators specialise largely on fishes and
freshwater crustaceans (the vibrant Azure Kingfisher, the
secretive Black Bittern and the common Eastern Great
Egret); others take a variety of smaller prey including aquatic
insects and molluscs (resident shorebirds such as Black‐
fronted Dotterels and migratory sandpipers), or in the case
of the iconic Black‐necked Stork (“Jabiru”), a diversity of
larger prey including frogs, snakes, fishes and turtles. The diversity of insectivorous birds (those species feeding on
insects) in the riparian zone is higher than any other group
(e.g. ~40% and 35% of species recorded in riparian habitats
of the Daly River and Fitzroy River, respectively; Fig. 10.2).
Some of these species are riparian specialists, for example
the Buff‐sided Robin and Purple‐crowned Fairy‐wren. Other
species such as the Shining Flycatcher, Rainbow Bee‐eater
(Fig. 10.3), Northern Fantail (Fig. 10.4) and Yellow‐tinted
Honeyeater occur in a variety of habitats but are often
associated with riparian zones. The ecological integrity of riparian zones across northern
Australia is increasingly being threatened by a range of
processes (including clearing, weed invasions and
disturbance by livestock; see Box 12) The deterioration of
riparian habitats has been cited as a principal reason for
local and regional declines in the northern Australian
endemic riparian specialists, the Buff‐sided Robin and the
Purple‐crowned Fairy‐wren (64). The western race of the
latter, which is restricted to the Victoria River District of the
NT and the Kimberley region of WA (mainly the Fitzroy River
catchment), is globally threatened. It requires dense riparian
vegetation and is most often found within 10 m of
permanent water; the maintenance of suitable riparian
vegetation is recognised as essential for its recovery and
survival. Chapter 3 ‐ 32
Northern Australia Land and Water Science Review full report October 2009 Box 10: Riparian zones – sustaining the rich bird fauna of the north
Red goshawk only nest in trees greater than 20 m in height
and within 1 km of water (65). In much of the savanna
country of northern Australia, such large trees can only be
found associated with streams and rivers. Figure 10.3. The Rainbow Bee‐eater (Merops ornatus) perched above a stream, ready to intercept an emerging aquatic insect. Photo: B. Pusey. Figure 10.5. The Red Goshawk (Erythrotriorchis radiatus), one of
the world’s rarest birds of prey and dependent on trees associated
with northern streams and rivers. Photo: P. Kyne. Figure 10.4. The Northern Fantail (Rhipidura rufiventris), a common bird in stream bank vegetation. Photo: P. Kyne. Another species critically dependent on the riparian zone is the Red Goshawk (Fig. 10.5). This species is one of the world’s rarest birds of prey and has experienced great reductions in distribution on the subtropical east coast. The major cause of this decline is habitat destruction by land clearing. Although this species does not specifically forage in riparian zones, such habitats provide vital nesting areas. Aquatic ecosystems in northern Australia Through the linkages between riparian vegetation, food
availability and natural river flows, the diverse and abundant
bird fauna of Australia’s northern catchments is critically
dependent on the maintenance of the integrity of riparian
systems. Peter Kyne (Tropical Rivers and Coastal Knowledge, Charles
Darwin University). Chapter 3 ‐ 33
Northern Australia Land and Water Science Review full report October 2009 Box 11: Dine in or out – riparian contributions to food webs
Riparian zones are the vegetated interface between terrestrial and aquatic ecosystems and have great ecological value (66). In northern Australia, riparian zones tend to be narrow as the harshness of the dry season climate places great physiological stress on vegetation growing even a short distance from the stream channel. Riparian vegetation may therefore represent the only lush, cool and moist habitat available in many parts of northern Australia during the dry season. Many insects that provide food for a variety of animals are found in riparian vegetation. Many of these insects are actually derived from the aquatic environment (Fig. 11.1) from where they emerge as adults and congregate in great numbers in the cool foliage of riparian plants. Here they are preyed upon by birds (see Box 10), reptiles, frogs, marsupials, spiders and other insects (Fig. 11.2). This contribution of aquatic‐derived organic carbon to terrestrial food webs is important in maintaining biodiversity in this habitat and for the savanna region as a whole. A well‐known example of such a predator is the Archer fish
(Toxotes chatareus) (Fig. 11.3). This species often patrols stream
margins searching for terrestrial insects in the foliage above. When
spotted, a well‐aimed jet of water is spat upward to dislodge the
insect prey from its perch and knock it down onto the water’s
surface where it may be consumed. Many other species of fish
consume terrestrial insects that fall on the water surface, including
rainbowfish, grunters and even barramundi. (a)
(b)
Aquatic
insects
600
400
200
Sa
va
nn
a
ne
zo
Rip
ari
an
dg
e
Wa
ter
's e
Mi
dw
ate
r
0
Habitat
Figure 11.1. Adult aquatic insects in the riparian zone. a) The relative contribution of adult aquatic insects to total insect abundance in the riparian zone. b) spatial variation in insect abundance across a gradient from the middle of the stream channel to savanna country 150m distant. Data sourced from Lynch et al. (67) for a study undertaken in Kakadu National Park. 60
Vertebrates
50
Fruit-Figs
40
Seed-Blossoms
Invertebrates
30
20
10
0
<8
0
80
-10
0
10
0- 1
20
12
0- 1
40
14
0- 1
60
16
0- 1
80
18
0- 2
00
20
0- 2
20
22
0- 2
40
24
0- 2
60
26
0- 2
80
28
0- 3
00
30
0- 3
20
It is not just a one‐way transfer of food however, for riparian zones also provide food for aquatic animals. Many northern Australian fishes consume insects from the riparian zone and this source of food may be especially important during the dry season when aquatic habitat and food production may be limited. Size‐related changes in diet of the black bream or sooty grunter
(Hephaestus fuliginosus) in northern rivers exemplify the
importance of riparian inputs into the stream environment (Fig.
11.4). Terrestrial insects comprise between 12 and 20% of the diet
in fish between 100 and 180 mm in length. In contrast, smaller fish
are almost entirely reliant on food sourced from the aquatic
environment. Terrestrial vertebrates such as small mammals and
reptiles are occasionally consumed by black bream. Seeds and
blossoms assume significance in the diet of fish greater than 180
mm in length as do the fruit of riparian trees. Figs are an especially
common fruit in the diet of large black bream. Figs are also
consumed by turtles and it is not uncommon in some northern
rivers to observe large black bream and a variety of turtles
congregating below a fig tree awaiting fruit to drop into the water.
Contribution of terrestriallyderived food to diet (%)
Insect abundance
Figure 11.3. An Archer fish scanning the vegetation above in search of its
next meal. Illustration: B. Pusey. Terrestrial
insects
800
Fish size (mm Standard length)
Figure 11.4. Changes in the types of riparian foods being eaten by black
bream as they grow. Data sourced from Davis and Pusey (unpublished). Figure 11.2. A predatory dragonfly resting in the riparian zone on a surprisingly chilly morning. Photo: B. Pusey. Aquatic ecosystems in northern Australia Elsewhere in tropical systems, frugivory by fish has been shown to
assist the dispersal of the seeds of riparian trees. Seeds are passed
intact through the digestive system and subsequently germinate
distant from their parent. This aspect of the feeding ecology of
black bream has not been studied in Australia but it is intriguing to
think that this species may help to cultivate its own food source. Brad Pusey and Mark Kennard (Tropical Rivers and Coastal Knowledge, Australian Rivers Institute, Griffith University). Chapter 3 ‐ 34
Northern Australia Land and Water Science Review full report October 2009 1.5 THE CURRENT CONDITION OF NORTHERN AUSTRALIAN AQUATIC ECOSYSTEMS The status of aquatic ecosystems and their responses to human impacts are commonly described using terms such as condition, biotic or ecological integrity, or health (71). The majority of rivers in the Australian tropics possess near‐natural flow regimes and are an ecological asset of global significance (72). The condition and ecological integrity of aquatic systems reflects the condition and integrity of the landscape they drain. Most aquatic ecosystems of northern Australia drain tropical/subtropical savanna landscapes. Globally, natural savanna landscapes have undergone dramatic declines in spatial extent due to human activities (only 30% remaining) and are typically in poor ecological condition (only 22% classified as in good ecological condition). Of this global savanna in good ecological condition, 90% is located in northern Australia) (19). Land tenure in Northern Australia is dominated by pastoral leases which include natural rangelands (e.g. savanna) and areas cleared for enhanced pasture production (19) (Fig. 12). Intensive cropping and horticulture is currently very limited in extent and as a consequence, impacts on aquatic ecosystems tend to be localised, except in certain areas such as in the upper Mitchell River or the Ord River. 90% of the world’s savannas assessed as being in good ecological condition are in northern Australia Proportion of total area (%)
100
80
Other
Cropping and horticulture
60
Pastoral lease
40
Aboriginal
20
0
Kimberley
Top End
Region
Gulf of Carpentaria
and
Cape York Peninsula
Figure 12. Proportion of different northern regions under different forms of land tenure. (data sourced from Woinarski et al., 19). There are currently no standardised broad‐scale assessments of the condition or ecological integrity of aquatic ecosystems across all of northern Australia. However, information exists for some aquatic ecosystem types in particular areas of the region, and some indirect measures of condition are available for the entire region. The River Disturbance Index (RDI) developed by Stein et al. (48) is one such indirect measure. The RDI is based on geographic data describing indirect measures of flow‐
regime disturbance due to impoundments, flow diversions and levee banks, and catchment disturbance due to urbanisation, road infrastructure and land use activities. The index quantifies disturbance for individual stream sections along a continuum from near‐pristine to severely disturbed. Based on this index, most northern Australian rivers are in the least disturbed categories. This is in stark contrast to the condition of many, if not most, rivers in south‐eastern and south‐
western Australia (Fig. 13). Aquatic ecosystems in northern Australia Chapter 3 ‐ 35
Northern Australia Land and Water Science Review full report October 2009 RDI
More
disturbed
0.6
>0.6
0.4
0.2
0
Less
disturbed
Figure 13. River Disturbance Index (RDI) (data sourced from Stein et al., 48). Other broad scale catchment condition assessments have also reported that the majority of northern Australian rivers are largely unmodified and in near‐natural condition (8). Two reasons above all others can put forward to account for this. First, rivers and streams are influenced by the landscapes through which they flow and, in general, the terrestrial landscapes of northern Australia are in good condition (19). Second, the natural flow regime remains intact for most rivers of northern Australia (49). These two characteristics are in marked contrast to the situation in southern Australia where many rivers are impounded, and many catchments substantially impacted by agriculture and urbanisation (8, 49). Overall, northern Australia’s rivers are in good condition because their flow regimes are usually unmodified and they drain relatively undisturbed catchments. Degradation is likely to follow intensification of landuse or disruption of natural flows. There are examples however, where rivers and wetlands of northern Australia are in less than pristine condition for one or more of a variety of reasons (e.g. flow regime modifications, road and water infrastructure, urbanisation, intensive clearing and agriculture, grazing, mining, invasive weeds and alien animals (see Box 12). We highlight here three examples, the Fitzroy, Daly and Mitchell Rivers. The condition of the Fitzroy River in the Kimberley region has been described as good, as have most rivers in the Kimberley region (73), yet recent rainfall/runoff models developed for this river indicate increased rates of runoff per unit rainfall indicative of catchment degradation by overgrazing (74). Localised but intense disturbances caused by human activities are evident in many northern Australian river catchments and alien plants and animals are causing widespread impacts Aquatic ecosystems in northern Australia Chapter 3 ‐ 36
Northern Australia Land and Water Science Review full report October 2009 Box 12: The twilight zone – alien invasions
The northern Australian landscape, especially its aquatic habitat, supports a large array of alien organisms (species introduced from other countries). Many plant species now recognised as invasive weeds were deliberately introduced into the environment to support pastoralism (75). Most animal pest species owe their presence to escape, abandonment or accidental release, although disturbingly, instances of translocation of feral pigs by ignorant hunters are known (76). Similarly the use of noxious alien fish species (e.g. tilapia) as live bait for barramundi fishing has been reported (77). Swamp buffalo (Bubalus bubalis) (Fig. 12.1) and feral pigs (Sus scrofa) (Fig. 12.2) are the most conspicuous of alien vertebrate pests degrading aquatic ecosystems of northern Australia. Buffalo were originally brought to Australia between 1825 and 1843 and released when the early settlements on Melville Island and Coburg Peninsula were abandoned in 1849. This population rapidly expanded and dispersed until it achieved a maximum population size of about 340,000 individuals in 1985 (78). Control of buffalo numbers was commenced in 1978 in Kakadu National Park and in 1985 buffalo were included in an eradication program (Brucellosis and Tuberculosis Eradication Campaign). This program has cost over $750 million in total (for all of Australia) and almost achieved total eradication before it ceased. Worryingly, buffalo numbers are once again on the increase. Figure 12.2. A feral pig gorging itself on road‐kill. Photo: D. Wilson. Pigs are omnivorous, eating a variety of wetland plants and tubers
as well as aquatic animals such as freshwater crayfish, frogs and
turtles. They also eat the eggs of ground nesting turtles, crocodiles
and riparian birds and have been implicated in the decline of
magpie geese in some areas. Pigs uproot and eat riparian seedlings
as they root along river banks in search of food. During the hottest
months, pigs wallow in the wet margins of water holes,
dramatically increasing the amount of suspended sediment in the
water column and decreasing water clarity. The physical
disturbance associated with wallowing may reduce the capacity of
wetlands to rejuvenate with the onset of summer rains. Both pigs
and buffalo spread noxious water weeds such as Mimosa pigra A smaller but no less threatening pest is the cane toad (Bufo
marinus). This toxic species is on the verge of colonising all of
northern Australia (it has recently been recorded on the eastern
border of the Kimberley region) and is spreading five times faster
than they did after the early years of introduction in 1935 (82).
Recent research has revealed remarkably rapid behavioural and
morphological evolution that has facilitated rapid dispersal. Toads
on the western colonising front now have longer back legs and
disperse further each night in comparison to toads in Queensland
(82). Figure 12.1. A swamp buffalo treading indelicately through a wetland in the upper Katherine River. Photo: B. Pusey. Buffalo have caused severe damage to wetland environments in the Northern Territory, including accelerated soil erosion and sedimentation, channelling of floodwaters, saltwater intrusion into freshwater habitats, loss of wetland vegetation and reductions in the diversity of wetlands plants and animals (79). Severe damage to northern wetlands has also been caused by feral pigs; their presence has been implicated in declines in riverine and wetland condition across the region. The distribution of this pest is largely limited by access to water as they are easily heat‐stressed (78). This, and the fact that they have relatively small home ranges (80), results in herds of pigs congregating around permanent waterholes and wetlands during the dry season (81), thus concentrating their activity and increasing their local impact.
Cane toads impact on native fauna in three main ways. First,
glands on its shoulders exude a very toxic poison which is capable
of killing most creatures that consume it (Fig. 12.3). Many native
predatory marsupials such as quolls have dramatically declined in
abundance as a direct result of toads. Water‐dependent species
such as the water monitor (Veranus mertoni) and freshwater
crocodiles also die if they ingest large toads. Second, toad larvae
are also toxic and may kill fish that eat them. Because they are
afforded protection by their toxicity, toad larvae may reach very
high abundances in waterholes and may compete with native frog
tadpoles for food resources. Third, large toads eat a variety of
small frogs, fish and invertebrates and, by virtue of their large
numbers, have the potential to dramatically alter local population
sizes of these animals and affect food availability for native
animals. Aquatic ecosystems in northern Australia Chapter 3 ‐ 37
Northern Australia Land and Water Science Review full report October 2009 Box 12: The twilight zone – alien invasions
to be dislodged by only the very largest of floods. Such mats have
been a persistent problem in irrigation areas such as the Burdekin
delta and have been shown to depress water quality and eliminate
native fish communities (83). Figure 12.3. A cane toad provides a last meal for a semi‐aquatic slaty grey snake Stegonotis cucullatus. Photo: D. Wilson. Invasive plants are also a threat to many waterways and floodplains of northern Australia. Four such weed species in northern Australia, Mimosa pigra, Hymenachne amplexicaulis, Cabomba caroliana and Salvinia molesta are listed as Weeds of National Significance because their impacts on natural and agricultural systems are so severe. These four species provide an illustrative spectrum of the ways weeds impact on aquatic systems. Mimosa pigra forms dense thickets on floodplains and on the margins of water holes. Such thickets monopolize space and nutrients and prevent access to permanent water by species such as water birds and wallabies. Hymenachne amplexicaulis is an introduced ponded pasture grass that invades permanent water bodies and seasonally inundated wetlands. Because it is capable of growing in several metres of water, Hymenachne can clog water ways sufficiently to prevent water movement and intensify flooding. Hymenachne forms dense stands that reduce native plant diversity and available habitat for native animals, particularly fish. It can also outcompete important native grasses. Cabomba caroliana is a fully aquatic plant that grows prolifically and is highly invasive. Its profuse growth ensures that it is able to quickly dominate waterways and it is therefore a serious problem in irrigation canals and impoundments as well as natural waterways. It secretes a sticky mucus around its leaves which inhibits consumption by herbivorous animals and reduces its value as fish habitat. When in dense stands in still waters, nocturnal respiration may cause dissolved oxygen levels to fall so low as to result in fish kills (due to asphyxiation). Its potential to interfere with aquatic food webs is extremely high. Salvinia molesta is a surface dwelling plant that also grows and reproduces extraordinarily rapidly. It may completely blanket the surface of water bodies (Fig. 12.4) in a very short time preventing the transmission of sunlight into the water column and effectively curtailing photosynthesis and primary production. Many other weeds occur across northern Australia but are not yet included as Weeds of National Significance despite them having substantial negative local impacts on aquatic systems. Examples of these alien plants include water lettuce (Pistia stratiotes), paragrass (Urochloa mutica) and water hyacinth (Eichorna crassipes). This latter species is of considerable concern for it may quickly establish surface mats that then become the substrate for other weeds, such as paragrass. This alien vegetation complex then becomes an impenetrable stable cover on the water’s surface able Aquatic ecosystems in northern Australia Figure 12.4 Salvinia molesta completely blanketing the surface of the
lower Howard River near Darwin. The inset in the upper right shows the
individual plants; note the presence of the native floating fern Azolla
pinnata. Photos: B. Pusey. Terrestrial weeds are also a threat to the ecologically important
riparian zones of northern rivers (see Box 11). They monopolise
space and prevent the establishment of seedlings of riparian
plants. In addition, they make the normally moist riparian zone
more prone to disturbance by fire. Weeds and alien pest animals are an important problem in the
north, not only because they reduce ecological integrity but
because they are economically costly. For example, degradation of
water quality in Cabomba infested water supply structures is
suggested to add $50 per megalitre in water treatment costs (84).
Similarly, weed control is economically costly. Hymenachne, for
which there is no effective biological control mechanism, requires
herbicide application every eight weeks in the initial phases,
frequently involving application from helicopters in large water
bodies, and then follow‐up application over several years (84).
Approximately $20 million was spent on herbicide treatment of
Mimosa in the Northern Territory between 1980 and 2004 with
little apparent success (85). Total eradication and ongoing
monitoring of Mimosa in Kakadu National Park is estimated to cost
$0.5 million per year (84). Not only is control of weeds costly but it has ecological costs as
well. For example, the herbicide Tebuthiuron is used for Mimosa
control. It is applied in pellet form at the onset of the first summer
rains to facilitate dissolution. It is highly toxic to aquatic
macrophytes and algae. It is a persistent (half life > 1 year) and
mobile chemical, so much so that the USEPA and manufacturer
guidelines suggest it not be used within 50 m of waterways! The
risk to aquatic plants is therefore high and this high risk may
persist for 10‐20% of species for almost a year (85). The
persistence of Tebuthiuron in the aquatic environment and
dramatic effects on aquatic plant life suggests that the flow‐on
effects on aquatic food webs are likely to be substantial. Brad Pusey and Mark Kennard (Tropical Rivers and Coastal Knowledge, Australian Rivers Institute, Griffith University). Chapter 3 ‐ 38
Northern Australia Land and Water Science Review full report October 2009 The overall condition of the Daly River in the Northern Territory was assessed as being in the good condition (83% of sites examined showed some modification, high cover diversity, low invasions by exotics), yet some assessment sites and some aspects of condition, particularly condition of the riparian zone, were assessed as being poor (86). Alien animals (pigs and buffalo) were identified as a significant threat, as were weeds. Greatest levels of disturbance and future threats were related to extensive clearing for broadacre cropping and horticulture (12). Specific instances of nutrient enrichment occur in the Douglas River catchment, a major subcatchment of the Daly River in which agricultural development has occurred (87). This is of concern as it highlights the potential for algal blooms. Ganf and Rea (88) undertook an assessment of the potential for blooms to occur in this and other rivers of northern Australia. They found that in natural circumstances nutrients were limiting; that is, nutrients were in short supply and that they were consumed before algal blooms could occur. More importantly, they found that the necessary inoccula for algal blooms, including species of toxic cyanobacteria (blue‐green algae), were present in northern Australian rivers, but were kept at very low biomass because of nutrient limitation. These findings indicate that if nutrients were no longer limiting (i.e. levels were increased because of anthropogenic activities) then algal blooms could occur. Indeed, blue green algal blooms have occurred in northern Australia under conditions of nutrient enrichment (54). With the addition of nutrients from agriculture, northern Australia’s rivers provide perfect conditions for toxic blue‐green algal blooms In the Gulf country of Queensland, the condition of study reaches in the Mitchell River catchment were rated as very good (29%) or good (56%) when condition was aggregated across all criteria in the Queensland State of the Rivers Assessment (89). Similarly, the AUSRIVAS assessment (based on aquatic macroinvertebrates) found most sites were equivalent to reference condition. However, specific sites were heavily impacted by nearby intensive agriculture, cattle grazing and mining, or by in‐stream activities such as gravel extraction (53, 90). Some subcatchments (e.g. the Palmer and the Walsh) have been identified as being more degraded than others (53, 91, 92). Floodplains of northern Australia remain largely intact although many floodplain areas have been heavily modified by feral animals such as pigs (Sus scrofa), domestic cattle (Bos taurus, B. indicus) and swamp buffalo (Bubalus bubalis) and plants such as mimosa (Mimosa pigra) and para grass (Urochloa mutica) (63, Box 12). The floodplain of the lower Ord is contrastingly highly impacted by the construction of the Ord River Dam as it now rarely receives flood flows sufficiently high to result in its total inundation (55) (see Box 8). These examples are typical of many northern Australian catchments; overall catchment condition is generally good yet there are specific areas where the condition of aquatic ecosystems is highly degraded. In addition, there are widespread diffuse threats from weeds and pests that, if left unchecked, may result in widespread degradation. Such threats are covered in the text below and in the case study boxes. The maintenance of ecological function of estuaries is vital for the economy of the north and for the integrity of upstream freshwater ecosystems Estuaries in northern Australian are largely unmodified or in near‐pristine condition, particularly when compared to estuaries in southern Australia which have undergone extensive modifications (Fig. 14). The most extensively modified estuaries in northern Australia occur near Darwin. Heavy metal residues occur in sediments of this estuary and it also receives treated sewage effluent (93). Pesticide residues occur in sediments and biota of the Ord River estuary and sediment dynamics have Aquatic ecosystems in northern Australia Chapter 3 ‐ 39
Northern Australia Land and Water Science Review full report October 2009 been greatly modified (55). The maintenance of ecological function of northern estuaries is vital for the economy of the north and for the ecology of upstream freshwater habitats. Maintenance of the natural flow regime is the chief means of achieving this protection (94). Proportion of estuaries (%)
1
extensively
modified
0.8
modified
0.6
largely
unmodified
0.4
near pristine
0.2
0
Kimberley
Northern
Territory
Queensland
Gulf of Carpentaria
Region
Australia
Figure 14. The condition of estuaries in northern Australia and Australia as a whole. Data sourced from NLWRA (8). A geographically comprehensive analysis of the condition of riparian zones has not yet been undertaken in northern Australia. A recent assessment scheme for riparian condition has been developed but results from its widespread application are not yet available (95). However, river condition assessments referred to above frequently take riparian condition into account. In such cases, they typically indicate riparian zones to be in moderate condition but also identify many instances were degradation occur and identify several threatening process. Chief among these are changes to the flow regime, large feral vertebrate pests such pigs and buffalo, and unrestricted access by cattle (96). The number of northern Australian wetlands currently included in the Directory of Important Wetlands Australia (including RAMSAR sites) is low compared to other areas of Australia (97, Fig. 15). They do however cover a comparatively larger area (Fig. 15b). RAMSAR listed wetlands are absent from the Gulf of Carpentaria, being limited to Kakadu and Coburg Peninsula in the Northern Territory and to the Ord River floodplain and Lakes Kununurra and Argyle (two man‐made habitats) in Western Australia. There are numerous other ecologically important wetlands in northern Australia (e.g. in the Fitzroy, Daly and Mitchell Rivers) that are also in relatively good condition. These should be considered candidates for inclusion in the Directory of Important Wetlands Australia and/or as RAMSAR sites. Aquatic ecosystems in northern Australia Chapter 3 ‐ 40
Northern Australia Land and Water Science Review full report October 2009 5000000
4500000
4000000
150
3500000
3000000
100
2500000
2000000
1500000
50
Total area (ha)
Number of listed wetlands
200
1000000
500000
Oc
ea
n
Tim
IX
or
-G
Se
ulf
a
Ca
rpe
nta
ria
XLa
ke
Ey
re
XI
Bu
ll-B
an
XII
c
-W
Pla
tea
u
t
VII
I-
Ind
SW
Co
as
VII
-
Gu
lf
SA
VI
-
V-
Ta
s
-M
DB
IV
III
-
SE
C
Co
as
II -
NE
I-
oa
st
0
t
0
Drainage Division
Figure 15. The number of wetlands included in the Directory of Important Wetlands Australia (top) and the collective area (ha) of listed wetlands within each of the Australian Drainage Divisions. 1.6 CHANGES IN AQUATIC ECOSYSTEMS IN RESPONSE TO ALTERED FLOW REGIMES The maintenance of the natural flow regime is critical to the integrity of aquatic ecosystems (4, 5). Changes in natural patterns of river flow due to changing land‐use, water resource development and from projected global climate change (98) are at the forefront of the many processes that threaten aquatic habitats and biota nationally (99) and globally (100). Changes in natural flow regimes due to changing land‐use, water resource development and projected global climate change are at the forefront of the many processes that threaten aquatic ecosystems in northern Australia 1.6.1 Groundwater and riparian extraction – ecological impacts of reduced water levels Maintenance of natural groundwater and surface water levels is key to sustaining many aspects of the dry season ecology of northern aquatic ecosystems. However, in an attempt to secure a reliable supply of water, humans often sink bores or wells to extract from groundwater or directly pump from surface river channels and waterholes (riparian extraction). This can severely affect natural groundwater levels and aquifer recharge rates, reduce dry season riverine baseflows and reduce the duration of persistence of dry season refugial waterholes. Maintenance of natural groundwater and surface water levels is key to sustaining the dry season ecology of northern aquatic ecosystems. Reduction in groundwater levels may directly impact on riparian vegetation as it struggles to maintain water balance during the dry season (101). It may also become more fire prone as a result. Perennial rivers such as the Daly and Roper Rivers have permanent baseflows due to significant Aquatic ecosystems in northern Australia Chapter 3 ‐ 41
Northern Australia Land and Water Science Review full report October 2009 groundwater inputs during the dry season. Lowered ground water levels affect delivery of water to the river channel, resulting in lower baseflows. This can reduce the availability and quality of important flow‐sensitive habitats such as shallow, fast‐flowing riffles. These are critical habitats for many fish species and are also important areas of production for aquatic invertebrates that form the food of larger species such as sooty grunter and barramundi (see Box 13). Reductions in water depth can also affect longitudinal connectivity as increasingly shallow areas become barriers to migration for a range of biota including turtles, fish and crustaceans. The potential for groundwater abstraction during the dry season in the Daly River to decrease the movement potential of the pig‐nosed turtle as it searches for places to lay its eggs was a key factor in the development of environmental flow limits in this river (101). Naturally isolated waterholes are a common feature of many intermittent rivers in northern Australia. They are critical refugia for water‐dependent biota and are key watering points for many terrestrial animals during the dry season. Waterholes are often sustained by connection to groundwater once surface flow has ceased. Waterholes denied this connection by lowered groundwater levels dry out more quickly and their value as refugia can be compromised by an unnaturally rapid deterioration in water quality (e.g. low dissolved oxygen and increased concentration of salts). Dry season waterholes may be the only source for aquatic refugia over many hundreds of kilometres of otherwise dry stream bed. The refuge provided by isolated waterholes therefore assumes great importance as they are the point from which recolonisation and dispersal along the river occurs once connectivity is restored by wet season flows. Human impacts on the spatial distribution and duration of persistence of dry season waterholes therefore can have far‐
reaching ecological consequences through space and time. Naturally isolated waterholes provide critical refugia for water‐dependent biota and are key watering points for many terrestrial animals during the dry season. Reduction in groundwater levels may impact on the ecology and biodiversity of subterranean ecosystems. Drawdown of groundwater so that subterranean systems are dewatered is likely to result in loss of the distinctive biota that inhabits these systems (see Box 6). Although poorly understood, it is also likely that subterranean ecosystems provide important environmental services (i.e. water purification, denitrification) (41) and their loss may have widespread and unforeseen consequences. The maintenance of groundwater ecosystems has deservedly been given high importance in environmental water plans in northern Australia (e.g. Katherine River in the Daly River catchment and the Howard River in the Darwin region). Aquatic ecosystems in northern Australia Chapter 3 ‐ 42
Northern Australia Land and Water Science Review full report October 2009 Box 13: The Daly – fish out of water?
20
Daly River
at Mt Nancar
1
re
t
ric
en
Fu
tu
Cu
rr
His
to
re
t
rre
n
Fu
tu
Cu
to r
ic
His
0
% reduction
from Natural
-5
-15
-5
-25
-35
-10
-45
-55
0.01
Extraction
scenario:
10
-65
1
-15
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.1
Extraction
scenario:
% reduction
from Natural
Discharge (cumecs)
10
100
Lower
Katherine
River
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
There is increasing pressure to develop the water resources of northern Australia but we currently have limited capacity to predict the consequences of altered flow regimes on aquatic plants and animals. The need to understand environmental water requirements of aquatic biota is particularly pressing in the Daly River catchment (101). Most of the Northern Territory’s current irrigation activity occurs in the Daly River catchment, and because of its constant dry season baseflow regime, reliable groundwater reserves and relatively good soils, further agricultural development, land clearing and water extraction are proposed for the area. But the Daly River is also recognised for its high conservation values (62). The Daly River supports a high diversity of freshwater and estuarine fish, including the critically endangered freshwater sawfish and the vulnerable freshwater whipray. It is also renowned as one of the country’s best rivers for recreational barramundi fishing. Fish are also of great value to indigenous inhabitants of the catchment. Because of their ecological, economic and cultural significance, the environmental flow requirements of freshwater fish in the Daly River have recently been investigated (102, 103). This information is being used to predict the ecological risks of alternative water use scenarios and inform water allocation planning in the catchment. Dry season water extraction (primarily from groundwater bores) is now concentrated in the vicinity of the lower Katherine River and main channel of the Daly River. The dry season flow regime of the river is little changed from natural because ‘Historic’ levels of extraction have been relatively minor (Fig. 13.1). However, substantial reductions in dry season baseflow discharge would occur if ‘Current water entitlements’ were fully utilized. Reductions in baseflows would markedly increase under a ‘Possible future entitlements’ scenario. These hydrologic impacts are most apparent in the lower Katherine River but are progressively ameliorated further downstream in the lower Daly River due to groundwater and tributary inputs to discharge. Semi‐quantitative risk assessment using conceptual models within a Pressure‐Vector‐Response framework (Fig. 13.2) identified several fish species at high risk from dry season water extraction (Fig. 13.3). These included large‐bodied fish of cultural and recreational importance (e.g. black bream, barramundi, mullet, sleepy cods) and less iconic, but nevertheless ecologically important species (e.g. blackmast, bony bream, rainbowfish and barred grunter). Proportion of time exceeded
Figure 13.1. Effects of different water extraction scenarios on dry
season flows in the lower Katherine River and the lower Daly River.
Flow duration curves show the proportion of time (dry season days)
each discharge was exceeded over the modelling period (spanning
1900–2008). Inset plots show the average (± SE) annual percentage
reduction in discharge for each water extraction scenario compared
with the ‘natural’ scenario. The four water extraction scenarios are:
‘Natural’ (i.e. no extraction), ‘Historic’ (i.e. estimated actual levels of
water extraction), ‘Current’ (i.e. current entitlements fully utilised)’,
and ‘Future’ (possible future entitlements). Modelled flow data was
provided by the Northern Territory Government Department of
Natural Resources, Environment, The Arts and Sport. Figure 13.2. Conceptual model of changes in physical and biological
characteristics of the Katherine‐Daly River system due to reductions in
baseflows and their potential effects of fish communities. Natural
baseflow regimes provide a variety of habitats and resources
supporting a range of fish species, age classes and trophic levels.
Reduction in baseflows due to water extraction (pressure) causes a
decrease in fish habitat quality and resource availability (response)
through a range of mechanisms (vectors). Aquatic ecosystems in northern Australia Chapter 3 ‐ 43
Northern Australia Land and Water Science Review full report October 2009 Box 13: The Daly – fish out of water?
15
20
25
Black bream
grunter
Higher Butlers
Barramundi
risk Ord River mullet
Sleepy cod
Giant gudgeon
Blackmast
Bony bream
Western rainbowfish
Barred grunter
Longtom
Exquiste rainbowfish
Macleay's glassfish
Fish species
Spangled perch
Tarpon
Toothless catfish
Black catfish
Snub-nosd garfish
Fly-specked hardyhead
Northwest glasfish
Mouth almighty
Golden goby
Hyrtl's tandan
Black-banded rainbowfish
Midgley's grunter
Archerfish
Purple-spotted gudgeon
Berney's catfish
False-spined catfish
Prmitive archerfish
Katherine River gudgeon
Swamp eel
Blue catfish
Salmon catfish
Shovel-nosed catfish
Empire gudgeon
Freshwater sole
Rendahl's catfish
Lower
Delicate blue-eye
risk
Pennyfish
30
Example
species:
13.4). However, if current water entitlements were fully
utilized, consequent changes to the dry season flow regime
and associated physical and ecological changes to the
riverine environment would increase the probability of low
and extremely low abundances of both species. This impact
is expected to be greatest in the lower Katherine River but is
lessened further downstream. For example, the probability
of sooty grunter abundances being low or extremely low
increases from 56% under natural flow conditions to more
than 75% under the current and future water entitlements
scenario. The impacts of dry season water extraction on fish
abundances are predicted to considerably lessen in the
lower Daly River system where hydrologic impacts of water
extraction are lower (Fig. 13.4). Similar responses to dry
season water extraction are predicted for barramundi (103). 100
Lower
Daly River
Katherine
at Mt Nancar
River
Cumulative probability (%)
Relative risk score
10
80
Natural
60
Historic
Current
Future
40
20
Extreme
Low
Moderate High
th
th
th
th
th
low
(10 -25
(25 -75
(>75
th
(<10
%'ile)
%'ile)
%'ile)
%'ile)
Extreme
Low
Moderate
th
th
th
th
low
(10 -25
(25 -75
th
(<10
%'ile)
%'ile)
%'ile)
High
th
(>75
%'ile)
Sooty grunter abundance
Fig. 13.4. Predicted changes in the abundance of black
bream (Hephaestus fuliginosus) in response to different dry
Figure 13.3. Relative risks of Katherine‐Daly River fish species to season water extraction scenarios for the lower Katherine
dry season water extraction estimated using a pressure‐vector‐
River and the lower Daly River. Predictions are derived from
response model. For each of 13 potential biophysical responses to a Bayesian Belief Network model (103) and are expressed as
a range of disturbance vectors (see Fig. 13.2), we ranked the cumulative probabilities of belonging to each abundance
relative risks of a negative impact on fish using three risk scores class (defined from the statistical distribution of quantitative
(high = 3, moderate = 2, low = 1) and summed these scores for each of 40 fish species present in the catchment (Kennard et al. fish abundance sampling data). unpublished). Our findings collectively indicate that several fish species are
Quantitative risk assessments (using Bayesian Belief Network potentially very sensitive to dry season water extraction. Dry
predictive models; Chan et al., 103) developed for two high‐
season flow regime changes due to historical water use are
risk species (black bream and barramundi) provide further minimal and consequently, little impact on fish abundances
evidence of the expected nature and degree of impacts from are expected so far. However, if current water entitlements
water extraction on fish populations in the Daly River. These were fully utilised we predict major impacts on several
assessments were based on modelled changes in dry season species (of ecological, recreational and cultural significance)
flow regimes under various water extraction scenarios (Fig in the Lower Katherine River. These impacts are lessened
13.1), combined with outputs from two‐dimensional habitat further downstream, where flow modifications are
simulation models of fish species’ hydraulic habitat ameliorated by tributary and spring inputs. We suggest that
requirements, and other scientific data, expert opinion and current and possible future water use entitlements should
Indigenous ecological knowledge. be revised in light of these findings. The predictive models reveal that historic levels of water Mark Kennard, Brad Pusey, Michael Douglas and Sue
extraction are unlikely to have affected natural variation in Jackson (Tropical Rivers and Coastal Knowledge). the abundances of sooty grunter and barramundi throughout the lower Katherine and Daly Rivers (e.g. Fig Aquatic ecosystems in northern Australia Chapter 3 ‐ 44
Northern Australia Land and Water Science Review full report October 2009 1.6.2 Physical infrastructure (dams, weirs, tidal barrages, pipes, canals and road crossings) – barriers to movement, transformation of riverine habitat, translocation of plants and animals Many northern Australian species of fish, crustaceans and other biota move extensively throughout river networks, on and off seasonally inundated floodplains and between freshwater and marine ecosystems. Such movements are necessary to complete life‐cycles and are vital for maintaining population sizes and genetic integrity. Water infrastructure developments such as dams, weirs and tidal barrages can significantly affect aquatic ecosystems. In addition to the way in which they alter natural flow regimes, they often form barriers to the longitudinal movement of biota and materials along river channels (see also Box 7). Barriers to movement can prevent access to upstream riverine habitats which are vital for development of many species of fish which spawn in estuaries (e.g. barramundi, sawfish, bullsharks and a host of other species) but can also spend much of their early lives in freshwaters, often far upstream. The impacts of barriers may therefore be felt in commercial fishery values (see Box 2). Cascading impacts throughout the riverine ecosystem can also occur because many such species are top predators and have an important role in structuring natural communities and in the way in which carbon and energy move through aquatic food webs. Freshwater crabs and prawns also migrate upstream after they have developed from larvae into juveniles in estuarine or downstream river habitats. Similarly, freshwater fish such as black bream (Hephaestus fuliginosus) and eel‐tailed catfishes (Neosilurus spp.) can be prevented from accessing tributary streams required for spawning. In the absence of such movement, local replenishment of populations diminished by seasonal drought or flooding cannot occur. The numerous ways in which physical infrastructure can potentially affect fish in northern Australian rivers is summarised in Table 2. Water infrastructure (dams, weirs and tidal barrages) can significantly affect aquatic ecosystems by altering natural flow regimes and forming barriers to the movement of biota and materials along river channels. Aquatic ecosystems in northern Australia Chapter 3 ‐ 45
Northern Australia Land and Water Science Review full report October 2009 Table 2. Potential impacts of physical infrastructure on fish in northern Australian rivers (modified from Kennard, 104). Source of impact • Change in riverine habitat from flowing to still water conditions within impounded area • Water abstraction and/or flow releases from impoundments resulting in artificial fluctuations in water levels within impounded area • Deterioration in water quality within and downstream of impoundment Mechanism of impact and potential consequences • May cause a change in native species composition to favour those species capable of utilising deep still water habitats for reproduction, foraging and refuge (e.g. bony bream, fork‐tailed catfish) and a decline in species favouring riverine habitat conditions is likely • Fluctuations in water levels expose previously inundated marginal areas potentially containing fish nesting sites (e.g. aquatic macrophyte beds utilised by small‐bodied species); can result in desiccation of fish eggs and larvae •
•
•
•
Stocking of large predatory fish in impoundments and increased predation by piscivorous birds Decrease in freshwater tidal/brackish water habitat if impoundment located at freshwater/estuarine interface Physical barriers to longitudinal movement •
•
•
•
•
•
•
•
Barrier effects dependent on relative position of barrier along river continuum Barrier effects likely to be cumulative •
•
Barrier effects may be ameliorated by the relative frequency of drownouts by high flows •
•
Interbasin transfers of water via pipelines and canals •
•
•
Proliferation of blue‐green algae and floating aquatic macrophytes, stratification of impounded waters and flow releases from bottom waters can cause degraded water quality conditions (e.g. low dissolved oxygen and temperature); may result in localised fish kills, a change in assemblage structure to favour those species tolerant of poor water quality (e.g. alien species), a decline in sensitive species and potentially interrupt cues for fish migrations and reproduction Potentially increased predation pressure within and upstream of impoundments and can have long‐term implications for food web structure, species composition and assemblage structure Can cause reduction in penetration of tidal prism and a decrease in overall amount of spawning and rearing habitat for larvae and juveniles; likely to lead to decrease in recruitment of many important recreational and commercial species (e.g. barramundi, mullet, mangrove jack, threadfin salmon) May prevent or hinder local and large‐scale movements by fully freshwater fish for foraging, spawning and/or dispersal of juveniles May prevent or hinder large‐scale movements of fish that require access to estuaries by: (1) trapping downstream spawning migrations of adult fish in weir pools thereby preventing access to estuarine and brackish water spawning habitat, and (2) preventing upstream dispersal of juveniles into freshwater habitats for foraging development and growth. May prevent or hinder movements of predominantly estuarine and marine fish into freshwater habitats for foraging, development and growth Barriers result in a decrease in overall amount of freshwater habitat accessible estuarine‐dependent fish Large numbers of upstream migrating fish may accumulate immediately downstream of barriers waiting for conditions suitable for upstream passage. These fish can be subject to increased levels of predation (by other fish, birds and crocodiles), competition and recreational fishing pressure If located close to river mouth, then impacts likely to be greater than if barrier is located high in catchment (as lower proportion of overall habitat is inaccessible) With increasing distance upstream, a succession of barriers is likely to progressively filter out species less capable of overcoming barriers; therefore, progressive downstream displacement of species less able to overcome barriers may occur However, actual drownouts that permit fish movement are likely to occur relatively infrequently for larger structures; although many fish will move during high flows (if seasonally appropriate), juveniles of some species may move only during low flow conditions, therefore, the ability of fish to overcome barriers during drownouts may be species and size class specific Increases the risks of translocating native fish between river basins thereby mixing distinct genetic stocks and threatening evolutionarily significant units. Increased likelihood of translocating noxious alien fish. Aquatic ecosystems in northern Australia Chapter 3 ‐ 46
Northern Australia Land and Water Science Review full report October 2009 The simple transformation of previously lotic (running water) to lentic (still) habitat in impoundments has major implications for species with an obligate need for lotic habitats (see Box 7). Elsewhere it has been demonstrated that fish populations present in streams feeding into reservoirs may become isolated from other such populations by the presence of deep water habitats in the reservoir which act as a barrier (105). Isolated populations are at greater risk of extinction from naturally occurring extreme events as they cannot be replenished by movement of individuals from nearby or even distant populations. Reservoirs, weirs and barrages may also act as barriers to the movement of materials other than biota. For example, the long residency time of water in impoundments allows much of the dissolved nutrient load to be removed by algae and aquatic plants and thus denied to downstream natural communities. Dissolved and particulate organic matter may be removed from the water column by biological activity or be deposited in the deep anoxic waters of the reservoirs and prevented from becoming incorporated into downstream food webs. Similarly, fine sediment may be trapped and no longer available for downstream and lateral transport in floodwaters, thus preventing the annual replenishment of floodplain habitats vital for natural communities as well as agricultural production. Transmission of sediment is also important for the maintenance of natural geomorphological processes and the maintenance of downstream habitat. Without continual replenishment, features such as sand bars are gradually diminished in size and abundance. Such habitats are crucial for reproductive success of freshwater crocodiles and turtles in northern Australia. Water quality in impoundments is often very different from that in rivers due to the absence of continual physical mixing. Stratification of the water column may develop as deeper waters become colder and more oxygen‐deficient than surface waters. This can result in much of the reservoir becoming unsuitable habitat for all but the most tolerant of species Interbasin transfers of water via pipelines and canals can pose a serious risk to native aquatic plants and animals in receiving river basins. There is an increased likelihood of translocating native biota between river basins thereby mixing distinct genetic stocks and threatening evolutionarily significant units, as well as an increased risk of translocating noxious pest species (see also Section 1.4.6 and Box 12). Although there are relatively few large dams across northern Australia (see Box 7), there are numerous smaller dams and weirs. Many such structures pose a barrier to the movement of aquatic organisms. An audit of the number of such barriers and the extent of river length denied to migratory species has not yet occurred. However, an assessment undertaken in the Gulf region alone identified artificial barriers to fish passage on two of three branches of the lower Nicholson River, the main reach of the Gregory River at the Doomadgee Crossing, both the Bynoe and Flinders channels in the lower Flinders River, the lower Norman River at Glenore Weir, the Leichhardt River at Kajabbi, at the Lake Mitchell, Lake Moondarra and Lake Julius spillways and numerous other smaller weirs and road crossings (106). Road crossings can also form artificial barriers to movement, particularly during low flow periods when many species of fish undertake dispersal movements throughout river networks (27). Any development of northern Australia is likely to involve expansion of the existing road network and may place further pressure on these migratory species. Road crossings often form barriers to movement of fish, prawns and other freshwater animals. Any development of northern Australia is likely to involve expansion of the existing road network and may place further pressure on these migratory species. Aquatic ecosystems in northern Australia Chapter 3 ‐ 47
Northern Australia Land and Water Science Review full report October 2009 1.6.3 Wet season floods – impacts of large dams and flood harvesting Changes to the flood regime of rivers have major geomorphological and ecological consequences. Reductions in the magnitude and frequency of floods reduce the ability of rivers to transport sediments downstream. Sediment accumulation causes a contraction in river channel size and reduction in overall habitat for biota. At smaller scales, wet‐season scour of sediments is vital for the maintenance of pools which otherwise become gradually infilled. Pools in rivers are important habitat for large fish (i.e. those targeted by recreational anglers) and as refugia during the dry season. Floods also help to mobilise and transport marine‐derived sediment delivered into estuaries by tidal movement. Without annual redistribution of such sediments, estuaries are at risk of becoming shallow and less diverse in structure as has occurred in the lower Ord River (55). Floods are required to inundate floodplain wetlands and provide lateral connectivity between the main channel and this important highly productive habitat. Reduction in the size, number and duration of floods decreases the area and depth of floodplains, the period in which biota may freely move between the main channel and the floodplain and the duration of floodplain waterhole persistence throughout the dry season. Floods have been clearly demonstrated to be important to commercial fisheries because of their role in determining the extent and availability of floodplains and saltmarsh habitats (see Box 2). Similarly, many migratory birds, including a large number of species covered by international treaties, are reliant on the provision of floodplain and supratidal habitats (see Boxes 3 and 4). Riparian vegetation may be disturbed by floods but ultimately reproduction, dispersal of propagules and age structure of riparian trees is dependent on the natural flood regime (58). Very large floods may act as a disturbance in both the in‐channel and off‐channel habitat, resulting in the uprooting of riparian trees and their transport into the stream channel (Fig. 16). Whilst such events may be seen as destructive, they are vital for the maintenance of natural processes and patterns. Wood is an important element of aquatic habitat structure. It provides cover for fish species, roosting points for birds, basking platforms for turtles and a stable hard substrate for algal and bacterial growth. It also provides diversity to stream habitats as flow‐mediated scour can create localised pools in otherwise shallow run habitats. Disturbance is a key feature in the ecology of lotic systems. In the absence of disturbance, some competitively superior species may build up in numbers and displace other species. Intermittent disturbance prevents this from occurring and maintains high levels of diversity. Figure 16. A riparian tree uprooted by wet season floods now provides important refuge habitat for fish and other biota. Photo: B. Pusey. Aquatic ecosystems in northern Australia Chapter 3 ‐ 48
Northern Australia Land and Water Science Review full report October 2009 Loss of floods can also affect the cues and conditions necessary for successful reproduction and recruitment of many northern fish species. They can also prevent access to floodplain habitats, inhibit longitudinal movement over structures which act as barriers during the dry season, reduce secondary productivity and the extent of floodplain habitat necessary for the growth of juveniles. Loss of wet season floods can affect the cues and conditions necessary for successful reproduction and recruitment of many northern fish species. Large impoundments have the capacity to greatly alter flood dynamics in rivers. The Ord River Dam, for example is capable of trapping all but the very largest of floods and a range of adverse ecological effects have been detected in this system (Box 8). Flood harvesting (i.e. the abstraction of large volumes of floodwaters for off‐stream storage) can similarly impact on flood dynamics. Small dams and weirs are unlikely to have great effect on flood dynamics because they typically have insufficient capacity to intercept large floods. However, such structures may be sufficiently large to trap small floods, particularly those that occur late in the dry season when water levels are low. Small flood events may be critical in maintaining water quality, and hence the survival of biota, of pools late in the dry season when temperatures are very high. 1.6.4 Dry season flow supplementation – flow releases from dam Flow supplementation occurs when water stored in impoundments is delivered down the stream channel. Typically, supplementation is restricted to the dry season when it is most needed by irrigators; thus it results in the artificial elevation of dry season flows. Upstream impoundments large enough to trap and hold sufficient quantities to guarantee water delivery throughout the dry season are typically associated with this form of water delivery. Changes in flow regime in the Ord River since construction of the Ord River Dam exemplify these changes. Wet season flows have been reduced by 67% and dry season flows have been increased by an enormous 439%, resulting in this formerly intermittent river becoming a perennial one with little clear distinction between wet and dry seasons (see Box 8). Among the environmental changes associated with flow supplementation in the Ord River include proliferation of aquatic plants and an increase in the abundance and average size of some fish species (55). It is not clear whether increases in size are the result of enhanced growth and survival of species or due to the absence of small recruits. Whatever the case, these changes have resulted in a major shift in the ecology of this river away from the natural condition. Downstream releases of relatively cold and anoxic water sourced from the bottom waters of large dams (either to supply irrigated agriculture or for hydroelectricity generation) can make many kilometres of river unsuitable habitat for freshwater plants and animals (107). Many fish rely on water temperature to cue reproduction so that it is in synchrony with the annual flooding cycle (27). Reproductive failure can result when hydrological and temperature cues become desynchronised. 1.6.5 Ecological impacts of climate change Projected changes to the Australian climate are likely to directly affect freshwater biodiversity, through losses of lowland freshwater habitats from saline intrusion due to rising sea level and increased storm surge, increased water temperatures, and increased variability and severity of extreme hydrological events (i.e. floods and droughts) (108, 109). In regions with high levels of Aquatic ecosystems in northern Australia Chapter 3 ‐ 49
Northern Australia Land and Water Science Review full report October 2009 consumptive water use, decreased water availability due to climate change is likely to impact disproportionately on the environmental share of surface water. Climate change in northern Australia is likely to directly affect freshwater biodiversity, through losses of lowland freshwater wetlands due to rising sea level and increased storm surge, increased water temperatures, and increased variability and severity of extreme floods and droughts There is inherent uncertainty in forecasting future changes in climate and the hydrologic cycle (110) and potential ecological responses to these changes (111). In simple terms, climate change will increase global temperatures and, through regional changes in precipitation, evaporation and runoff, make some areas of northern Australia wetter and others drier. This will redistribute freshwater systems but dispersal capacity and geographical and human barriers will limit colonisation of freshwater biota to new locations. Fish are particularly vulnerable to increased habitat fragmentation and alterations to both temperatures and river flows. Their ability to move between different habitat patches is critical for life‐cycle completion and many aspects of their biology and ecology are intimately linked with variation in thermal and hydrological regimes through space and time (112). Therefore, substantial reshuffling of species composition within and among river catchments can be expected due to extinctions of non‐mobile freshwater‐dependent species, range expansions of mobile and marine tolerant species, and potentially greater rates of invasion by introduced species tolerant of human disturbances (113). Changes in species distributions and abundances can also lead to cascading impacts on other freshwater biota through aquatic food webs (e.g. due to changes in the intensity of biotic interactions such as predation and competition) (Fig 17). ↑ Temperature
↑ Sea Levels
∆ Precipitation
↑ UVB-Radiation
↑ Evaporation
∆ flow
regime
∆ Stratification
∆ Stream & floodplain
geomorphology
= habitat changes
Connectivity
Physical & flow-related habitat
requirements of biota
∆ Species distribution & abundance
∆ 1 o & 2o
production
∆ Water chemistry
Environmental Tolerances of Biota
∆ Food web dynamics
∆ Ecosystem processes
Figure 17. Conceptual model of broad climate change impacts on freshwater ecosystems (source: F. Sheldon and M. Kennard, unpublished). Although there is substantial uncertainty around the extent to which rainfall may change in response to global climate change, there is general agreement that in tropical regions, there will be fewer, but Aquatic ecosystems in northern Australia Chapter 3 ‐ 50
Northern Australia Land and Water Science Review full report October 2009 more intense rainfall events (114). Changes in rainfall result in magnified runoff responses (115) which are likely to alter hydrologic regimes. However, there is still a great deal of uncertainty associated with these predictions; moreover predicted changes in hydrology vary greatly between regions and rivers of northern Australia. None‐the‐less, if rainfall does become more episodic and those episodes more intense, it is likely that floods will become larger and of shorter duration. Such changes are likely to result in greater distinction between wet and dry seasons. Class 10 streams (see above), the most common flow regime type in northern Australia, are likely to shift more towards the Class 12 streams typifying the inland periphery of northern Australia. Class 3 streams are likely to shift more towards Class 10 streams if more episodic rainfall does not adequately recharge the aquifers responsible for providing the sustained baseflows typifying this flow regime type. Fewer floods of short duration may inundate floodplains but may not enable prolonged exchange of biota and materials between floodplains, river and estuary. Such floods are more likely to act as disturbance events, mobilizing sediments and changing channel form A 2‐4 °C rise in air temperature is predicted for tropical regions by 2100 (116). Evaporation rates will increase significantly as the temperatures rise and this may impact on the persistence time of refugial waterholes in intermittent rivers and wetlands on floodplains. Decreased dissolved oxygen (DO) concentrations, a function of temperature as well as oxygen availability, may impact on many species as DO levels in tropical waters are typically naturally low (117). In the tropics, many terrestrial ectotherm fauna are already approaching thermal tolerances (118). Elevated temperature may also impact upon food webs as metabolic rates typically increase with increasing temperature (66). Sea level rise is one of several impacts predicted under a global warming scenario (114) and although there is little doubt that sea levels are indeed rising, there is a considerable degree of uncertainty about the magnitude of change. The IPPC predicts a maximum increase of 0.59m by the end of the century (114). Many northern wetlands are located only minimally above sea level (and in some cases, below it) and are at extreme risk from sea level rise (119). Finlayson et al. (120) predicted that a rise in sea level in the Alligator Rivers region would result in loss of existing mangrove forests followed by upstream change in their distribution, a concomitant loss of Melaleuca wetlands and a transformation of existing freshwater wetlands to saline flats. In areas of very low gradient such as the Gulf of Carpentaria, the upstream extension of saline water and inundation of freshwater wetlands may occur over a vast spatial scale. In the Kimberley region, sea level rise combined with the extreme tidal range typical of this region could impact severely on floodplain habitats given the relatively small contribution that this habitat type makes to total catchment area (<20%) (Fig. 8). If the severity of monsoonal storms increases, as is predicted (114), then the potential area inundated by storm surges is likely to increase with an increase in sea level, further impacting on coastal wetlands and floodplains. Such changes would impact greatly on species that are obligate floodplain dwellers or use floodplains at critical phases of their life history (e.g. many species of estuarine and freshwater fish, waterbirds and migratory birds). 1.7 CHANGES IN AQUATIC ECOSYSTEMS IN RESPONSE TO OTHER HUMAN ACTIVITIES 1.7.1 Agriculture (including broad­acre and mosaic) Agricultural developments can impact aquatic ecosystems in many ways including increased sedimentation, nutrient enrichment, contamination with biocides and other chemicals, changes in runoff rates and increased likelihood of alien weed invasions (121). Importantly, the effects of Aquatic ecosystems in northern Australia Chapter 3 ‐ 51
Northern Australia Land and Water Science Review full report October 2009 agriculture on aquatic systems may be persistent and difficult to correct, thus agriculture may have significant negative legacy effects. Agricultural impacts on aquatic systems are varied, persistent and difficult to correct. The effects of increased sedimentation, nutrient enrichment, biocide contamination, changes runoff and groundwater recharge rates, and alien weed invasions continue to affect northern Australian aquatic ecosystems. Sediment mobilised by agricultural activity and delivered to aquatic environments via runoff has a variety of deleterious physical and ecological effects. Fine sediments in suspension increase turbidity and decrease light transmission thus reducing primary production. When they settle out from the water column, fine sediments blanket hard surfaces reducing their suitability as a substrate for periphyton, further depressing primary production. Deposition of fine sediments can reduce habitat quality for bottom‐dwelling animals (e.g. by infilling the interstitial spaces of sand and gravel stream beds) and suspended sediments may also clog the gills and respiratory surfaces of invertebrates and fishes. Prolonged increases sediment loads can ultimately result in changes in river channel form, the loss of pools through in‐filling and an overall reduction in habitat diversity. Nutrients applied to crops often find their way into aquatic environments and may do so in large and damaging quantities. For example, Rayment (122) reported that 50% of all nitrate in river environments draining from catchments supporting sugar cane production was derived from these areas despite the fact that they comprised only 13% of the area. In the Ord River regions, high nutrient loads derived from irrigated cropping have been reported (see Box 8). Nutrient enrichment can massively increase rates of primary production (the process of eutrophication) potentially causing blooms of toxic blue‐green algae and proliferation of filamentous algae. Filamentous algae are not particularly palatable or digestible for many aquatic animals and so cannot sustain natural aquatic foods webs in contrast to periphyton and diatoms. High nutrient concentrations can accelerate litter breakdown rates through increased microbial activity and may cause decrease in dissolved oxygen and a shift from sensitive species to more tolerant, often non‐native species. Similarly, high nutrient loads can also stimulate excessive macrophyte growth. Macrophytes provide critical habitat for many species of small freshwater fish in northern rivers (27), but excessive growth results in an overall reduction in habitat diversity and quality. In still or slowly flowing waters, macrophyte proliferation can result in pronounced diurnal changes in oxygen availability as nocturnal respiration reduces dissolved oxygen levels, often so low that other aquatic biota asphyxiate. The senescence and breakdown of large biomass of aquatic plants in isolated pools places further demands on dissolved oxygen availability. Contaminants arising from agricultural practices include pesticides, herbicides and heavy metals (see section on mining below). Other than directly toxic effects, biological impacts on aquatic organisms (e.g. invertebrates and fish) from these chemicals include increased rates of physical deformities, impacts on behaviour such as the propensity for larval invertebrates to disperse in the water current (drift), reduced growth rates and increased deformities, reductions in reproductive capacity and a host of other effects. In tropical Australia, the rate of delivery of contaminants from agricultural lands to aquatic ecosystems may be significant. For example, a single large rainfall event in the Pioneer River catchment in eastern Queensland resulted in the transport of an estimated 470 kg of the herbicide Diuron into the Dumbleton Weir. Residues of a range of other herbicides derived from cane lands, including amtryn, atrazine, hexazinone and 2,4‐D, were also detected in the weir after this event in 2002 (122). Cotton production in Australia has historically relied on the use of an enormous array of biocides to control insect and weed pests (60). Although the use of some pesticides commonly used in the 1970s (e.g. DDT) had ceased in 1981, residues of this pesticide and its Aquatic ecosystems in northern Australia Chapter 3 ‐ 52
Northern Australia Land and Water Science Review full report October 2009 breakdown products (DDE and DDD) were still detectable in the Darling River over a decade later (see also Box 10). Agricultural development may also alter runoff rates and stream yield processes. Clearing of natural vegetation increases runoff rates, as does soil compaction associated with the construction of service roads. Such changes can alter the stream hydrograph (typically making flow events larger and more flashy) but also facilitating the transport of sediments and chemicals. These effects are especially pronounced when riparian zones are degraded and no longer provide a buffer between terrestrial and aquatic environments. Agricultural impacts on aquatic ecosystems may be highly persistent in time and spatially extensive. Many of the impacts described above are particularly associated with, but not limited to, broad‐acre agriculture. Despite the patchy nature of mosaic‐style agriculture, they may still have widespread impacts across river‐floodplain ecosystems. Whilst best‐practice irrigation should see no water exiting from cropped areas during the dry season, high intensity rainfall events during the wet season will still result in the mobilisation of sediments and residual fertilizer and toxicants. In addition, the development of road infrastructure to service widespread and patchy mosaic‐style development is likely to have its own suite of impacts (e.g. barriers to movement, increased rates of erosion, etc.). Despite the patchy nature of mosaic‐style agriculture, they may still have widespread impacts across river‐floodplain ecosystems. Widespread extraction of groundwater to irrigate mosaic style agriculture is likely to reduce groundwater inputs to river systems and cause drawdown of groundwater in subterranean systems. Whilst careful monitoring of aquifers may be used to regulate the extent of this impact, this may be more difficult in areas with diffuse, poorly‐recognised aquifers, where the links between aquifer recharge and subsequent discharge to river systems are poorly understood or where the distribution and needs of groundwater dependent ecosystems are unknown. 1.7.2 Rangeland and high­density cattle production The ecological impacts of cattle grazing continue to be felt over much of northern Australia given the widespread nature and long history of the cattle grazing industry in the region. Cattle may impact aquatic habitats via a variety of mechanisms. Soil compaction and reduction of groundcover in rangelands and the formation of ramps and trails through the riparian zone influence runoff dynamics and stream yield (123, 124). Reduced infiltration capacity of the soil and the extent to which rainfall is able to enter the stream as interflow or baseflow, increases the amount of rainfall moving into stream systems as overland flow and affects both high and low flows. Increased rates of runoff lead to an increase in the frequency of flood events with such events having steeper rising and falling arms of the flood hydrograph (123). Reduction in infiltration capacity and groundwater inputs leads to reduced dry season flows and greater distinction between wet and dry seasons. Cattle spend a significant portion of their day within the stream channel or sheltering in the shade of riparian vegetation especially in semi‐arid regions resulting in the trampling and loss of function of springs (125). Loss of spring inputs results in a reduction in flow during the dry season. The loss of springs coincident with European settlement has been reported for large areas of northern Queensland and is predicted to have negative impacts for the maintenance of biodiversity (126). The addition of nutrients to aquatic systems via urine and faeces whilst cattle are sheltering in the shaded riparian zone or wading in the stream itself has significant potential to impact on nutrient levels and aquatic food webs, especially in streams of low nutrient status such as those occurring over much of northern Australia. Aquatic ecosystems in northern Australia Chapter 3 ‐ 53
Northern Australia Land and Water Science Review full report October 2009 Cattle impacts on freshwater ecosystems are amplified because cattle are attracted to water for drinking, bathing and shade. Erosion associated with cattle grazing when stocking rates are excessive has been reported across northern Australia. Perhaps the most dramatic example occurred in upper tributary watersheds of the Ord River catchment where the amount of sediment liberated as a result of loss of groundcover was sufficient to cause concern for the long‐term future of the capacity of the planned impoundment on this river (127). Development of high density cattle production (i.e. feedlots) needs to be carefully managed as the transport of sediment and nutrients at times of high runoff into nearby streams may have far‐reaching ecological impacts (see above). 1.7.3 Mining and other extractive industries Widespread and persistent negative ecological impacts associated with mining have occurred in northern Australia (e.g. Rum Jungle Uranium mine in the Finniss River catchment and the Palmer River goldfields in the Mitchell River) (91, 128, 129); these are however, the result of activities occurring many decades in the past. Current mining activities are better managed but even in the most stringently monitored of mines, direct and indirect effects on aquatic ecosystems are still possible. For example, sediment inputs from both operating and rehabilitated mine sites have been recorded as contributing to suspended sediment loads in receiving waters (130, 131, 132). In‐stream mining activities such as gravel extraction or rerouting of channels are an especially effective means of liberating sediments, decreasing water clarity (90). The recent expansion of the McArthur River zinc‐lead‐silver mine in the Gulf of Carpentaria (involving a large open‐pit mine in the existing river bed and diversion of the McArthur River proper) provides an extreme example of the gross changes to aquatic habitat integrity that can result from mining operations. Many mines also have extensive associated road networks and road density has been shown to be directly correlated with the extent of erosion in northern Australia (92). Past mining activities have cased widespread and persistent negative ecological impacts. Current mining activities are usually better managed but even in the most stringently managed of mines, direct and indirect effects on aquatic ecosystems can still occur Runoff from mine sites and associated infrastructure may also carry materials other than sediment (128). Stream acidification associated with mining is of special concern in northern Australia as depressed pH levels can facilitate the liberation of naturally occurring substances such as aluminium which interfere with respiration in gilled animals such as fish and cause widespread mortality (fish kills) (128). Increased concentration of heavy metals originating from mine sites can either directly kill some aquatic organisms or indirectly alter food web structure. For example, dissolved copper is toxic to many aquatic animals when present in sufficiently high concentrations, but more importantly, when present in even low concentrations, is toxic to a variety of species algae and aquatic macrophytes. This can reduce habitat diversity and have cascading effects on aquatic food webs, ultimately affecting the diversity and abundance of aquatic biota such as insects, crustaceans and fish. 1.7.4 Tourism and recreation Aquatic ecosystems in northern Australia Chapter 3 ‐ 54
Northern Australia Land and Water Science Review full report October 2009 Natural environmental values (i.e. scenic value, high ecological integrity) are a key attractant for tourists and water in the landscape provides a focus for recreational and tourism‐oriented activities. The focus on water as a destination may become especially intense during the dry season when water becomes scarce (133) and, accordingly, impacts associated with recreation may be most intense at this time. Permanent waterholes in naturally intermittent rivers and perennially flowing rivers or tributaries may therefore experience very high rates of visitation. The nature of the tourism‐related impacts to aquatic environments has been little studied in northern Australia but Hadwen et al. (133, 134) list a diverse range of activities and their impacts gleaned from a review of studies undertaken elsewhere in Australia. Recreational fishing is prominent amongst these activities, given its importance in the daily life of the inhabitants of the region and the reason why tourists visit the north (especially those of domestic origin) (19). For example, over 100,000 tourists visit the Gulf of Carpentaria annually and 90% of tourists’ surveyed list recreational fishing as among the primary reasons for visiting the region (135). Over‐exploitation of target species such as barramundi (Lates calcarifer) has been demonstrated in heavily fished areas (27). The translocation of alien fish pest species used as live bait for barramundi has also been identified as a significant risk (77), as has the collection of bait itself (chiefly, the freshwater prawn species Macrobrachium in rivers such as the Daly River; Fig. 18) (Pusey and Kennard, personal observations). Recreational bycatch of conservationally significant species such as the endangered sawfish (Pristis microdon) has been shown to result in high mortality for this long‐lived species. The saw‐like rostrum is sometimes retained as a trophy and the carcass left to rot on the river bank (136). Even when done with the best of intentions (i.e. catch and release), concern about the sustainability and impacts of recreational fishing continue to be expressed world wide (137, 138, 139). Recreational fishing is among the primary reasons that many thousands of tourists visit northern Australia each year. However, over‐fishing and other impacts associated with water‐oriented recreation and tourism threaten aquatic ecosystems in northern Australia Aquatic ecosystems in northern Australia Chapter 3 ‐ 55
Northern Australia Land and Water Science Review full report October 2009 Figure 18. The migratory freshwater prawn Macrobrachium sp., an important recreational species as well as a key component in aquatic food webs. Photo: B. Pusey. Boating can negatively affect the aquatic environment. The wake generated by power boats driven at high speed can increase the rate of bank‐side erosion resulting in loss of riparian vegetation, isolation or loss of bank‐associated structures (undercut banks and woody debris) and increase sediment inputs and turbidity (133, 140). Changes in habitat and food‐web structure as a result are likely to alter the abundance of fish species targeted by anglers. Hydrocarbon inputs (e.g. oil and fuel) increase in areas of high boat use (140). The unintended translocation of nuisance aquatic weed species on boat trailers and outboard motors has been identified as of concern in northern Australia (141). Other impacts associated with water‐oriented recreation and tourism include changes in terrestrial animal density due to construction of tracks and access points (142, 143), changes in food web dynamics either through re‐suspension of sediments and nutrients, and the addition of nutrients in the form of human waste, urine, litter and detergents (144, 145). Such changes in nutrient concentration or availability are likely to assume significance in the nutrient‐poor waters of many northern Australian freshwaters. The unintended introduction of toxicants into the aquatic environment is also associated with recreational use of water bodies. For example, detergents in stream systems not only add nutrients (especially the often limiting nutrient phosphorus) but, because of their surfactant properties, break down the water’s surface tension. Many sunscreens have a similar action. Whilst seemingly trivial, many species of aquatic invertebrates are critically dependent on an intact surface tension for movement and respiration. Insect repellents contain toxicants which when added to the aquatic environment may impact on aquatic fauna. This is especially important when visitation rates are high and high numbers of mosquitoes and flies and prolonged exposure to harmful UV rays are perceived Aquatic ecosystems in northern Australia Chapter 3 ‐ 56
Northern Australia Land and Water Science Review full report October 2009 as annoying and potentially injurious to health; these are the exact conditions most likely to occur around swimming holes in northern Australia. 1.7.5 Urbanisation Degradation of freshwater ecosystems associated with urban development occurs via a variety of pathways. The impervious surfaces of roads increase runoff dramatically, hastening the delivery of water to streams and rivers. Flashier hydrographs are the result, which in turn can lead to channel erosion. Water exiting such surfaces also carries a variety of pollutants such as oils and other hydrocarbons, nutrients, herbicides and pesticides originating from garden and park areas. Urban areas require domestic water supply (see Box 7) and wastewater treatment facilities. Effluent from such works is frequently discharged into nearby creeks and rivers. 1.8 ASSESSMENT OF POTENTIAL ECOLOGICAL CONSEQUENCES OF FLOW REGIME CHANGES UNDER FUTURE CLIMATE AND DEVELOPMENT SCENARIOS FOR KEY ENVIRONMENTAL ASSETS IN THREE CASE STUDY RIVERS The Northern Australian Sustainable Yields (NASY) quantified hydrologic changes expected under a range of future climate and development scenarios for 43 key environmental assets across northern Australia (146). Hydrological regimes were modelled under four scenarios: Scenario A – historical climate change and current development; Scenario B – climate for the last 11 years and current development; Scenario C – 2030 climate change and current development; Scenario D – 2030 climate change and 2030 development of farm dams, plantations, groundwater systems and proposed irrigation development. Scenario A provided the baseline against which hydrologic changes under the other three scenarios were assessed. Scenario B represents recent conditions in which rainfall has been higher than the long term average. Scenario C is based upon results from 15 global climate change models (GCMs) which provide a large range of expected future climate regimes. The modelled changes for the extreme ‘wet’, ‘mid’ and extreme ‘dry’ predictions are reported and denoted as Cwet, Cmid and Cdry, respectively. Scenario D results were based on the Scenario C model predictions with the addition of proposed future developments (denoted Dwet, Dmid and Ddry, respectively). A series of potentially ecologically relevant hydrological metrics were estimated from the modelled data for each asset and scenario (146). In addition, ‘site‐specific’ metrics based on published studies of the environmental flow requirements of a particular asset were also estimated for each scenario. However, this was restricted to just three of the 43 assets because of a general lack of detailed studies of environmental flow requirements of aquatic biota in northern Australia and inadequate knowledge of the specific relationships between hydrology and ecology for most rivers of the region. Very few detailed studies of environmental flow requirements of aquatic biota have been undertaken in northern Australia. Inadequate knowledge of the relationships between hydrology and ecology therefore make it difficult to accurately predict the consequences of altered flow regimes. Aquatic ecosystems in northern Australia Chapter 3 ‐ 57
Northern Australia Land and Water Science Review full report October 2009 Here we draw on the results of McJannet et al. (146) to briefly assess potential ecological consequences of flow regime changes under future climate and development scenarios for key environmental assets in three case study rivers: 1) the Camballin Floodplain (Le Livre Swamp System) in the Fitzroy River catchment; 2) the middle reaches of the Daly River at Oolloo Crossing; 3) the Mitchell River Fan Aggregation (a large aggregation of floodplain waterbodies) in the Mitchell River catchment. 1.8.1 Fitzroy River at Camballin Weir Morgan et al. (147) believed that flows corresponding to 8.0 GL.day‐1 were necessary to initiate fish movement over the Camballin Weir. Flows above 28.8 GL.day‐1 allowed completely unimpeded movement. It was also assumed that this flow is sufficient to result in floodplain inundation. Under current average conditions (scenario A), flows sufficient to initiate and enable fish movement over the weir was estimated to occur on average for 69 days per year (Table 3). Completely unimpeded fish movement and flooding of the Camballin Floodplain was estimated to occur for 42 days per year. The generally higher rainfall that has occurred over the last 11 years (Scenario B) increased in the number of days above these thresholds by around 25%. The extent of this change is far greater than any estimated for either the Cwet or Cmid climate change scenarios. The most extreme dry climate change prediction however results in a substantial reduction in the number of days available for fish movement over the weir and the number of days over which floodplain inundation is expected to occur. Table 3. Modelled current and future specific flow metrics necessary for (1) commencement of fish passage and (2) unimpeded fish passage and floodplain inundation at Camballin Weir, Fitzroy River. Values given are the number of days per year that specific metrics are exceeded (Scenario A) and the extent and direction of change under Scenarios B, C and D. nm = not modelled. (sourced from McJannet et al., 146). Metric A B Cwet Cmid Cdry Dwet Dmid Ddry ‐1 (1) # of days > 8.0 GL.day
69 +27.6 +3.9 ‐1.7 ‐15.9 nm nm nm (2) # of days > 28.8 GL.day‐1 42 +24.9 +3.3 ‐1.1 ‐12.3 nm nm nm The broader ecological consequences of these predicted hydrologic changes are difficult to assess given the current state of knowledge. However, it is likely that both the reduction in ability of migratory fish to move within the catchment and the extent of floodplain inundation would impact on the production of fish within the river. Further reduction in the ability to move upstream may impact heavily on the already threatened sawfish Pristis microdon. A reduction in the frequency and duration of floodplain inundation would presumably reduce the extent of flooded area which would likely impact upon waterbirds (see Boxes 2 and 3). If a reduction in the number of days in which water inundated the floodplain also resulted in a change in persistence time then it is likely that some of the biota would have insufficient time to develop fully (i.e. fledge in the case of waterbirds) and would become trapped in the isolated and diminishing floodplain wetland. 1.8.2 Daly River at Oolloo Crossing Aquatic ecosystems in northern Australia Chapter 3 ‐ 58
Northern Australia Land and Water Science Review full report October 2009 Environmental flow metrics defined for the Daly River (101) relate to the ecological requirements of pig‐nosed turtles (Carettochelys insculpta), ribbonweed (Vallisneria nana) and riparian vegetation (see also Box 13). The first threshold value of 1.04 GL.day‐1 is needed to maintain conditions suitable for turtles nesting and ribbonweed habitat whereas the second value of 0.17 GL.day‐1 was needed to supply sufficient water to sustain riparian vegetation during the dry season. Predicted changes in flow required to maintain turtle habitat and conditions for the growth of the ribbonweed varied under the different scenarios (Table 4). Under natural conditions (Scenario A), 151 days per year were suitable for turtle nesting (i.e. dry sand banks) and ribbonweed growth in the Oolloo area. Recent flows have been greatly elevated (Scenario B), potentially resulting in insufficient time for turtle eggs which are deposited in nests during the late dry season to develop fully before wet season inundation. Similarly, conditions may have been too wet for prolific growth of ribbonweed beds (also an important food source for turtles). It is thus likely that pig‐nosed turtle recruitment and survival has declined in the Oolloo region in response to the reduction in nesting habitat and food availability. Under the Cwet and Dwet scenarios there were at least 47 fewer days below the 1.04 GL.day‐1 threshold, suggesting that potential impacts on turtles might occur under these scenarios. In contrast, the mid and dry scenarios increased the number of days below this threshold by 10 – 56 days. Whilst this suggests that conditions required for turtle nesting and ribbonweed growth would be met, the increased duration of low flow conditions may impact on other aspects of the biology of turtles (e.g. the need to move between river reaches). Predicted hydrologic changes had no impact on the number of days above the threshold value required to meet the evapotranspirative needs of riparian vegetation at Oolloo Crossing under any scenario (Table 4). We caution that it is inadvisable to base environmental flow assessments on a single species or a single aspect of its biology as meeting the requirements of these criteria may be to the detriment of other species and ecological process (148). Table 4. Modelled current and future specific flow metrics to maintain conditions for (1) turtles and ribbonweed and (2) riparian vegetation in the middle Daly River at Oolloo Crossing. Values given are the number of days per year that specific metrics were not exceeded (Scenario A) and the extent and direction of change under Scenarios B, C and D. (sourced from McJannet et al., 146). Metric A B Cwet Cmid Cdry Dwet Dmid Ddry (1) Days < 1.04 GL.day‐1 151 ‐139.6 ‐49.1 +9.8 +45.3 ‐47.7 +13.4 +56.3 (2) Days < 0.17 GL.day‐1 0 0 0 0 0 0 0 0 Environmental flow recommendations or water allocations to suite a single species or a single aspect of its biology is risky as it may be detrimental to the flow requirements of other species and ecological process. The best way to avoid this is to ensure that natural patterns flow regime variability is maintained. 1.8.3 Mitchell River Fan Aggregation The Mitchell River Fan Aggregation is a large aggregation of river channels and floodplain waterbodies in the lower part of the catchment. Under historical conditions (Scenario A), the flow regime of the Mitchell River at the Mitchell River Fan Aggregation is highly seasonal with over 97% of annual flow occurring during the wet season (Table 5). Dry season flows only rarely ceased completely and flows sufficient to inundate the floodplain occurred for 18 days per year. Recent changes (Scenario B) to this pattern have been minimal, in contrast to that recorded for rivers of the western portion of northern Australia. The wettest of the climate change scenarios predicts an Aquatic ecosystems in northern Australia Chapter 3 ‐ 59
Northern Australia Land and Water Science Review full report October 2009 increase in both wet and dry season volumes with more prolonged flooding. Both Cmid and Cdry scenarios are expected to result in moderate to substantial change in flood dynamics (number of high flow days and total wet season flow). In addition, significant changes to dry season flows are predicted (i.e. more prolonged low flow duration and a substantial increase in the number of zero flow days under the Cdry scenario). Thus, extreme climate change is predicted to result in less flooding, shorter duration of connectivity between the main channel and floodplain water bodies and more prolonged and intense periods of low flow. Table 5. Modelled current and future specific flow metrics for the Mitchell River Fan Aggregation. Threshold values are given in the text above. Values given are the extent and direction of change of individual metrics under Scenarios B, C and D relative to Scenario A. Note that Scenario A does not include current development. (sourced from McJannet et al., 146). Metric Unit A B Cwet Cmid Cdry Dwet Dmid Ddry Annual flow GL 6790 +3% +40% ‐6% ‐26% nm nm nm (mean) Wet season flow GL 6620 +3% +40% ‐6% ‐26% nm nm nm Dry season flow GL 164 +2% +29% +12% ‐37% nm nm nm Number of days Days 36.5 ‐2.7 ‐3.7 +13.5 +44.7 nm nm nm below low flow threshold (mean) Number of zero Days 6.1 ‐0.7 ‐0.2 +6.2 +21.3 nm nm nm flow days Days 18.3 +0.6 +7.2 ‐1.2 ‐4.9 nm nm nm Number of days above floodplain inundation threshold (mean) Impacts occurring as a result of these hydrological changes arising from climate change are likely to be profound. A reduction in dry season flow will result in a reduction in longitudinal connectivity and restriction of movement of aquatic biota due to low water depths over connecting channels. Biota will be isolated in refugial waterholes for longer than previously. Consequent reductions in water quality and habitat availability coupled with increased predation and competition for limited resources are likely to result in a reduction in fish abundance and diversity. Coupled with a reduction in the production expected to occur on the floodplain as a result of decreased connectivity and extent of flooding, overall reduction in production of freshwater biota is expected to occur. 1.9 WHAT ARE THE POSITIVE AND INTENDED OUTCOMES ARISING FROM CHANGES TO FLOW REGIMES? It is difficult to envisage how human‐induced changes in flow regimes are positive for aquatic ecosystems if they result in deviations from the natural ranges of variation in ecologically important flow regime attributes. If these deviations occur, they are very likely to cause changes to the natural aquatic ecosystem structure and function. We do not consider these anthropogenic changes to natural flow regimes (whether or not they are ‘intended’) to be ‘positive outcomes’ for aquatic ecosystems. By way of example, impoundments may create new habitats utilised by a range of biota and subsequently become valuable tourist assets. For example, Lakes Argyle and Kununurra form Aquatic ecosystems in northern Australia Chapter 3 ‐ 60
Northern Australia Land and Water Science Review full report October 2009 extensive lacustrine habitats proving highly suitable habitat for some species of waterbirds; so much so they were listed as RAMSAR sites. However, this is difficult to reconcile with the damage caused by loss of natural riverine habitats of these now flooded areas, changes to estuary dynamics, reduction in size and frequency of floods and hence major change to the flood regime of downstream floodplains and waterbodies (e.g. Parry’s Lagoon), denial of most of the river length to migratory fish species, and other consequential ecological impacts. 1.10 IF CHANGES IN WATER REGIME WERE TO OCCUR, WHAT WOULD BE REQUIRED TO MINIMISE THE NEGATIVE IMPACTS ON AQUATIC ECOSYSTEMS? Risk‐mitigation options will, at best, only partially minimise the negative impacts of flow regime changes and water infrastructure on aquatic ecosystems As human activities continue to alter aquatic ecosystems in northern Australia, a critical conservation goal is to predict how aquatic biota and ecosystem processes will respond to changing environmental conditions. This will allow development of dynamic mitigation, restoration and conservation strategies to adapt to these anthropogenic threats. Unfortunately however, scientists and natural resource managers in Australia generally lack the knowledge required to achieve this goal. Nevertheless, a broad conceptual understanding, informed by evidence from specific case studies and research conducted in northern Australia and elsewhere (e.g. 5, 99, 149), does allow a number of general principles to be articulated concerning strategies to minimise the negative impacts of water resource development associated flow regime changes. These strategies include (but are not limited to) the following: •
Ideally, detailed environmental flow assessments should be undertaken for all existing and future water resource developments so that the flow requirements of aquatic biota and risks of hydrological change for aquatic ecosystems can be evaluated and mitigated. This would guide the choice of appropriate mitigation strategies (listed below). •
Water resource developments should be strategically located to avoid impacts on high conservation value aquatic ecosystems. •
Water infrastructure (dams, weirs, tidal barrages) should be as “hydrologically transparent” as possible (bounded by infrastructure constraints and reductions in yield). This means that natural flow events (e.g. floods, flow pulses, baseflows, low flow spells) from upstream would be delivered to the downstream side of a dam with minimal interception (i.e. storage within the impoundment). This would help to maintain ecologically important components of the flow regime for downstream aquatic ecosystems. •
Dams should be fitted with multi‐level offtakes to minimise the release of poor quality water downstream (e.g. release of bottom waters of low temperature and dissolved oxygen). •
Dry season flow releases from dams that result in artificially elevated low flows (e.g. for delivery of water for irrigation purposes) could be avoided by delivery of the water through offstream pipelines instead of along the river channel and offstream storage at the destination. •
Flow releases from dams that result in unnaturally rapid rises and falls in water levels downstream and within impoundments should be avoided due to the risk of stranding of aquatic organisms, nesting areas, etc. •
Sediment bypass measures may be used to mitigate clearwater‐erosion and substrate changes caused by sediment load deficits downstream of dams and larger weirs. Such measures could include installation of gates on water infrastructure to minimise impedance to sediment transport or removal of accumulated bedload from impoundments and reintroduction downstream. Aquatic ecosystems in northern Australia Chapter 3 ‐ 61
Northern Australia Land and Water Science Review full report October 2009 •
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Flood harvesting and offstream storage could be used mitigate the requirement for instream storages. Harvesting of floodwaters should only be considered in circumstances where changes to ecologically important components of the natural flood hydrograph (e.g. rates of rise and fall, peak magnitude) can be minimised and the location of offstream storages can be situated in areas that don’t affect habitat for important terrestrial and aquatic biota. Some impoundments provide ideal habitat for growth of aquatic weeds. In situations where the problem is severe, it may be feasible to reduce such plant growth by manual harvesting or biological control. Groundwater extraction should proceed with extreme caution given the critical uncertainties that exist in terms of environmental water requirements of groundwater ecosystems. Riparian extraction of water from streams and rivers can lead to major reductions in low flows and increases in the frequency and duration of dry spells. Similarly, water extraction from isolated waterholes can reduce the duration of persistence and quality of these important dry season refugial habitats. These impacts could be mitigated by setting minimum thresholds for dry season water extraction by riparian users and adequately policing these regulations. Pump offtakes should be positioned well below the water surface to minimise the possibility of removing high quality surface waters from deep stratified waterholes. For high priority aquatic habitats (e.g. those known to be critical dry season refugia and/or supporting species of conservation significance), individual site‐specific management rules should be established to protect their ecological values, including specification of permissible drawdown depths and rates. Ecological impacts could also be minimised if riparian extraction was undertaken during high flow conditions rather than during low flow periods. However, this would require suitable storage capacity to be provided offstream (e.g. farm storages), given that the greatest demand for water is usually at times of low flow (i.e. during the dry season). Installation of effective fish passage devices (e.g. rockramp fishways, fish ladders, fish locks, fish lifts, etc) on all existing and new water infrastructure should be a priority (this also applies to small gauging weirs and road crossings). Provision of specific environmental flow allocations to render these fish passage devices effective should also be ensured. However, it should be noted that fish passage devices can never fully restore natural fish passage and can at best, only allow movement of a subset of the fish that actually desire to do so. Dams and weirs may also impede passage of other aquatic and water‐dependent biota (e.g. crustaceans, turtles, crocodiles). It is therefore critical that their passage requirements (i.e. in terms of depths, velocity and turbulence in fishways) also be provided for. Interbasin transfers of water should be avoided due to the risk of translocation of native and alien organisms. Maintenance of the integrity of riparian zones upstream and downstream of impoundments is critical. Any redundant water resource infrastructure (e.g. dams and weirs no longer in use) should be removed. Collection of long‐term baseline environmental and ecological data for key ecosystem assets should be undertaken prior to any water resource development and/or implementation of threat mitigation strategies (such as environmental flow releases and fish passage devices). Thereafter, ongoing monitoring of the ecological impacts or efficacy of the threat mitigation strategies should be performed and these strategies revised and implemented within an adaptive management context. Aquatic ecosystems in northern Australia Chapter 3 ‐ 62
Northern Australia Land and Water Science Review full report October 2009 1.11 WHAT ARE THE CRITICAL KNOWLEDGE GAPS PREVENTING SOUND ANSWERS TO QUESTIONS ABOVE? The prospect of dramatic environmental changes over the next century underscores the need for innovative science and new decision‐support tools for efficiently managing and conserving freshwater ecosystems in northern Australia. This will enhance the capacity of natural resource managers to implement effective mitigation and adaptation programs and should aid greatly in the environmentally sustainable economic and social development of Australia (see also Blanch, 150). In particular, we need to develop spatially explicit scenario evaluation tools for northern Australia’s river catchments to consider transparent trade‐offs of different development and climate scenarios. These would be underpinned by research on the following: 1. Water resource management and planning: • Ecological thresholds and environmental water requirements. We currently have limited capacity to predict the consequences of altered flow regimes on aquatic plants and animals. The main channel has received some attention and there needs to be additional effort on better understanding low‐flow ecology. The ecological water requirements of floodplain systems remain virtually unstudied yet these are likely to be critical for the health of aquatic ecosystems. This needs to be underpinned by better modelling of groundwater‐surface water interactions. • Connectivity and movement. Links between the river ecosystems and the estuarine zone (in both directions) need to be better understood. In particular, the role of fauna (e.g. fish and crustaceans) in maintaining connections between components of the river‐floodplain system and the environmental triggers for movement of different species and life stages are important knowledge gaps. We also need to better understand the connectivity to estuarine and coastal processes and the implications of more intensive land use for these ecosystem and the assets they support, such as commercial and recreational fisheries (see below). • Systematic monitoring of aquatic ecosystem health across the region using indicators based on current work to identify critical processes and key species for monitoring as well as the approaches being trialled through the Framework for the Assessment of River and Wetland Health (FARWH) in tropical Australia. • Systematic conservation planning including river connectivity. Research is needed to develop tools and apply them to identify and prioritise high conservation value aquatic ecosystems. Once identified, these areas need to be managed appropriately to maintain their high conservation values (e.g. through legislative, natural resource management and land‐use planning instruments; Blanch, 150). 2. Understanding the impacts of land use intensification on river‐floodplain, estuarine and coastal ecosystems. • We currently lack the tools and underlying science to predict how intensive land use will affect the fluxes of water, sediment, nutrients and other contaminants to river and coastal ecosystems. New agricultural developments in Northern Australia combined with a program of scientific monitoring and assessment will provide an opportunity to integrate planning, management and science within an adaptive cycle. Not only would resource management benefit from access to available knowledge and tools, the science development would benefit from the learning gained from such large‐scale ‘natural experiments’. • Prediction of the sediment and nutrient loads coming from different land use units is a major knowledge gap. There is a need to identify and quantify the key processes and mechanisms which generate sediment and nutrient loads and how these change in response to changes in landscape position, land‐use, hydrology and management/mitigation. Aquatic ecosystems in northern Australia Chapter 3 ‐ 63
Northern Australia Land and Water Science Review full report October 2009 •
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4. Similarly, we need better information to help predict the movement and fate of agrochemicals, particularly in groundwater systems better understanding of surface water groundwater interactions. We need a much better understanding of the effects of the above changes in material fluxes on ecological processes. As well as the focus on in stream processes, this should include greater consideration of the riparian zone as a critical interface between land and river ecosystems. In addition to studying more intensive land management such as irrigated agriculture, this should also consider some of the flow on effects of intensification such as weed and feral animal impacts and altered fire regimes. Managing coastal development to maintain healthy rivers, estuaries and coasts. With increased focus on developing catchments, water resources and coastal areas, there is also a growing need to better understand the potential trade‐offs involved in these decisions. So more research is needed to improve our relatively poor understanding of coastal processes and to identify effective indicators and monitoring approaches for the estuarine zone. Planning for and adapting to climate change impacts on tropical rivers, coasts and communities. • Better predictions of the implications of climate change on water resources for northern Australia are emerging, but the environmental and ecological consequences and the opportunities for adaptation need to be fully quantified. • This also applies to the implications of rising sea levels for coastal ecosystems, particularly for low‐lying coastal wetlands and floodplains. • Thermal tolerances and thresholds of aquatic biota are also poorly understood for most flora and fauna in northern Australia. This makes it difficult to identify and appropriately manage species most at risk from climate change. 1.12 SUMMARY 1.12.1 What are the critical links between aquatic ecology and development of northern Australia? The ecology of aquatic ecosystems in northern Australia is fundamentally linked to the seasonality of the climate, the low nutrient status of the landscape, and above all, the natural flow regime. The movement of water and associated nutrients, carbon and energy between different hydrosystem components of aquatic ecosystems and the maintenance of connectivity is vital for natural ecosystem function. Development in northern Australia that severs these links is likely to result in a loss of ecological integrity and loss of value. 1.12.2 What is the current status of aquatic ecosystems? Most aquatic ecosystems of northern Australia are currently in good condition and of high national and global value. Specific instances of localised degradation occur throughout the north and are associated with urbanisation, irrigated agriculture, pest animal and weed species and mining. These localised disturbances provide an indication of how future development may impact on aquatic ecosystems. Aquatic ecosystems in northern Australia Chapter 3 ‐ 64
Northern Australia Land and Water Science Review full report October 2009 1.12.3 What is the immediate prognosis of the health of northern Australian aquatic ecosystems? Under current levels of development there is little reason to believe that the condition and ecological integrity of northern Australia’s will deteriorate greatly. None‐the‐less, where current levels of development have been demonstrated to impact on aquatic systems, remediation measures would be beneficial. Ignoring the threat posed by pest animals and weeds is likely to result in gradual deterioration in some regions; a threat it would be beneficial to address. Changes in condition associated with predicted global climate change are probably unavoidable if efforts to reduce the rate or direction of change in climate change are unsuccessful. It is important to note however, that the capacity for natural systems to resist or accommodate such changes is entirely dependent on maintenance of natural condition, natural function and natural processes. 1.12.4 What are the likely future pressures or trajectories? One of the most likely future pressures appears to be the expansion of a mosaic‐style agriculture drawing heavily upon groundwater for irrigation. Large irrigation schemes based on large storages seems unsustainable given the demonstrated failure and ecological impacts of such schemes in northern Australia in the past and the difficulties such schemes pose in northern Australia (109). Mosaic‐style agriculture, however, is not a panacea for these problems. It is unlikely to be environmentally benign as it is likely to rely heavily on groundwater for irrigation needs as well as a host of other potentially negative consequences for natural aquatic ecosystems (see Section 1.7). The other clear and present danger for aquatic ecosystems is the inexorable spread and damage caused by introduced animals and plants (see Box 12). 1.13 ACKNOWLEDGMENTS We sincerely thank Peter Bayliss, Michele Burford, Ian Halliday, Bill Humphreys, Peter Kyne, Neil Pettit and Julie Robins for writing their feature boxes at such short notice, Michael Douglas, Stuart Bunn and Peter Davies for constructive comments and advice (particularly the section on knowledge gaps), Doug Ward for assistance with maps, and Dave Wilson, Neil ArmstrongTony Pusey and Michael Pusey for photographs. We also appreciate the guidance and constructive suggestions provided by Peter Stone, Richard Cresswell and other participants in the Northern Australia Land and Water Taskforce project. Funding support for this project was generously provided by the Department of Environment, Water, Heritage, and the Arts through the Tropical Rivers and Coastal Knowledge (TRaCK) Commonwealth Environmental Research Facility. Aquatic ecosystems in northern Australia Chapter 3 ‐ 65
Northern Australia Land and Water Science Review full report October 2009 1.14 REFERENCES 1. Costanza R, d’Arge R, de Groot R, et al. (1997) The value of the world’s ecosystem services and natural capital. Nature 387, 253–260. 2. Baron J, Poff NL, Angermeier PL, et al. (2002) Meeting ecological and societal needs for freshwater. Ecological Applications 12, 1247–1260. 3. Mount R, Auricht C, Prahalad V and Scheltinga D (2009) Australian National Aquatic Ecosystem Classification Scheme ‐ Version 0.9. Updated DRAFT, June 2009. report for the Department of the Environment, Water, Heritage and the Arts. 4. Poff NL, Allan JD, Bain MB, et al. (1997) The natural flow regime: a paradigm for river conservation and restoration. BioScience 47, 769–784. 5. Bunn SE and Arthington AH (2002) Basic principles and consequences of altered hydrological regimes for aquatic biodiversity. Environmental Management 30, 492–507. 6. Winter TC (2001) The concept of hydrologic landscapes. Journal of the American Water Resources Association 37, 335–349. 7. Naiman R.J., Latterell J.J., Pettit N.E. and Olden J.D. (2008) Flow variability and the vitality of river systems. Comptes Rendus Geoscience 340, 629–643. 8. NLWRA (2002) National Land and Water Resources Audit. Catchment, river and estuary condition. Natural Heritage Trust, Canberra. 9. Halliday IA and Robins JB (2007) Environmental flows for sub‐tropical estuaries: understanding the freshwater needs of estuaries for sustainable fisheries production and assessing the impact of water regulation. Final report FRDC Project No. 2001/022 Coastal Zone Project FH3/AF. 10. Vance DJ, Staples DJ and Kerr JD (1985) Factors affecting year‐to‐year variation in the catch of banana prawns (Penaeus merguiensis) in the Gulf of Carpentaria, Australia. Journal du Conseil International pour l'Exploration de la Mer 42, 83–97. 11. Robins JB, Halliday IA, Staunton‐Smith J, et al. (2005) Freshwater‐flow requirements of estuarine fisheries in tropical Australia: a review of the state of knowledge and application of a suggested approach. Marine and Freshwater Research 56, 343–360. 12. Bayliss P, Bartolo R and van Dam R (2008) Quantitative Ecological Risk Assessments. In R Bartolo, P Bayliss and R van Dam (eds.) Ecological risk assessment for Australia’s northern tropical rivers: Sub project 2 of Australia's Tropical Rivers ‐ an integrated data assessment and analysis (DET18). A report to Land and Water Australia. Environmental Research Institute of the Supervising Scientist, Darwin, Australia. 13. Drinkwater KF and Frank KT (1994) Effects of river regulation and diversion on marine fish and invertebrates. Aquatic Conservation: Freshwater and Marine Ecosystems 4, 135–151. 14. Halliday IA, Robins JB, Sale B and Marsh RW (2005) Freshwater flow requirements of estuarine fisheries: data review and research needs. Final Report for Land and Water Australia Tropical Rivers Program Project No QP155. 15. QPIF (2008) Queensland Primary Industries and Fisheries. Viewed 9 October 2009, <http://www.dpi.qld.gov.au/documents/Fisheries_SustainableFishing/ASR‐GoC‐Inshore‐Fin‐
2008.pdf>. 16. Ozcoasts (2009) Viewed 9 October 2009, <http://www.ozcoasts.org.au>. 17. Coleman APM (2004) The national recreational fishing survey: The Northern Territory. Northern territory Department of Business, Industry and Resource Development. Fishery Report 72. 18. Gillanders BM and Kingsford MJ (2002) Impact of changes in flow of freshwater on estuarine and open coastal habitats and the associated organisms. Oceanography and Marine Biology: an Annual Review 40, 233–309. 19. Woinarski J, Mackey B, Nix H and Traill B (2007) The nature of northern Australia. Natural values, ecological processes and future prospects. ANUE Press, Canberra. Aquatic ecosystems in northern Australia Chapter 3 ‐ 66
Northern Australia Land and Water Science Review full report October 2009 20. Petheram C and Bristow KL (2008) Towards and understanding of the hydrological factors, constraints and opportunities for irrigation in northern Australia: a review. CRC for Irrigation Futures Technical Report No 13/08. 21. Poff NL and Ward JV (1989) Implications of streamflow variability and predictability for lotic community structure: a regional analysis of stream flow patterns. Canadian Journal of Fisheries and Aquatic Sciences 46, 1805–1818. 22. Kennard MJ, Pusey BJ, Olden JD, et al. (2009) Classification of natural flow regimes in Australia to support environmental flow management. Freshwater Biology doi:10.1111/j.1365‐
2427.2009.02307.x. 23. GeoSciences Australia (2006) GEODATA TOPO 250K Series 3. Shape files format. Commonwealth of Australia (GeoSciences Australia). 24. Eliot M and Eliot I (2008) Report 2: Estuaries. In: Lukacs GP and Finlayson CM (eds.) A compendium of ecological information on Australia’s northern tropical rivers. Sub‐project 1 of Australia’s tropical rivers – an integrated data assessment and analysis (DET18). A report to Land and Water Australia. National Centre for Tropical Wetland Research, Townsville, Queensland. 25. Wolanski E, Moore K, Spagnol S, et al. (2001) Rapid, human‐induced siltation of the macro‐tidal Ord River estuary, Western Australia. Estuarine, Coastal and Shelf Science 53, 717–732. 26. FAO (2007) The World’s Mangroves 1980‐2005: A thematic study prepared in the framework of the Global Forest Resources Assessment. FAO, Rome. 27. Pusey BJ, Kennard MJ and Arthington AH (2004) Freshwater fishes of north‐eastern Australia. CSIRO Publishing, Collingwood, Victoria. 28. Franklin DC (2008) Report 9: The waterbirds of Australian tropical rivers and wetlands. In: Lukacs GP and Finlayson CM (eds.) A compendium of ecological information on Australia’s northern tropical rivers. Sub‐project 1 of Australia’s tropical rivers – an integrated data assessment and analysis (DET18). A report to Land and Water Australia. National Centre for Tropical Wetland Research, Townsville, Queensland. 29. Stein JL, Hutchinson MF, Pusey BJ and Kennard MJ (2008) Ecohydrological classification based on landscape and climate data. Appendix 8 In: Pusey BJ, Kennard MJ, Stein JL, et al. (eds.). Ecohydrological regionalisation of Australia: A tool for management and science. Innovations Project GRU36, Final Report to Land and Water Australia. Available at: <http://lwa.gov.au/products/pn22591>. 30. Frissell CA, Liss WA, Warren CE and Hurley MD (1986) A hierarchical framework for stream habitat classification: viewing streams in a watershed context. Environmental Management 10, 199–214. 31. Pusey BJ, Kennard MJ and Arthington AH (2000) Fishes of the dune field of Cape Flattery, northern Queensland and other dune systems in north‐eastern Australia. Ichthyological Exploration of Freshwaters 11, 65–74. 32. Delaney R, Fukuda Y and Saalfeld K (2009) Management program for the magpie goose (Anseranas semipalmata) in the Northern Territory of Australia, 2009–2014. Northern Territory Department of Natural Resources, Environment, the Arts and Sport, Darwin. 33. Bayliss P, Bunn S, Douglas M, Davies P (in prep) Decadal trends in rainfall, river flow and aquatic ecosystems in northern Australia in relation to the ENSO‐IPO interaction: implications for long‐
term water policy and management. 34. Junk WJ, Bayley PB and Sparks RE (1989) The flood pulse concept in river‐floodplain systems. Canadian Journal of Fisheries and Aquatic Sciences 106, 110–127. 35. Lewis WM, Hamilton SK, Rodriguez MA, et al. (2001) Foodweb analysis of the Orinoco floodplain based on production estimates and stable isotope data. Journal of the North American Benthological Society 20, 241–254. 36. Pettit NE, Bayliss P, Davies PM, et al. (2009) Seasonal contrasts in carbon resources and ecological processes on a tropical floodplain. Unpublished manuscript. Tropical Rivers and Coastal Knowledge, University of Western Australia. Aquatic ecosystems in northern Australia Chapter 3 ‐ 67
Northern Australia Land and Water Science Review full report October 2009 37. Webb JW (1991) The influence of season on Australian crocodiles. Pp 125–131 In: Haynes CD, Ridpath MG and Ridpath MAJ (eds.) Monsoonal Australia: landscape, ecology and man in the northern lowlands. Balkema, Rotterdam. 38. Harvey KR and Hill GJE (2003) Mapping the nesting habitat of saltwater crocodiles (Crocodylus porosus) in Melacca Swamp and the Adelaide River wetlands, Northern Territory: an approach using remote sensing and GIS. Wildlife Research 30, 365–375. 39. Georges A and Merrin L (2008) Freshwater turtles of tropical Australia: compilation of distributional data. Report to the CERF Tropical Rivers and Coastal Knowledge, Charles Darwin University. 40. Georges A (1987) The Pig‐nosed Turtle ‐ Warradjan. Australian Natural History 22, 230–234. 41. Humphreys WF (2008) Rising from down under: developments in subterranean biodiversity in Australia from a groundwater fauna perspective. Invertebrate Systematics 22, 85–101. 42. Gibert J, Danielopol DL and Stanford JA (eds.) (1994) Groundwater ecology. Academic Press, London. 43. Boulton AJ, Fenwick GD, Hancock PJ, Harvey MS (2008) Biodiversity, functional roles and ecosystem services of groundwater invertebrates. Invertebrate Systematics 22, 103–116. 44. Wilkens H, Culver DC, Humphreys WF (eds.) (2000) Ecosystems of the world, vol. 30. Subterranean Ecosystems. Elsevier, Amsterdam. 45. Wilson GDF (2008) Gondwanan groundwater: subterranean connections of Australian phreatoicidean isopods (Crustacea) to India and New Zealand. Invertebrate Systematics 22, 301–
310. 46. Burrows DW (2004) A review of the aquatic management issues and needs for the Northern Gulf NRM Planning region. Report 04/16, Australian centre for Tropical Freshwater Research, James Cook University, Townsville. 47. Doupe RG, Knott MJ, Schaffer J and Burrows DW (2009) Investigational piscivory of some juvenile Australian freshwater fishes by the introduced Mozambique tilapia Oreochromis mossambicus. Journal of Fish Biology 74, 2386–2400. 48. Stein JL, Stein JA and Nix HA (2002) Spatial analysis of anthropogenic river disturbance at regional and continental scales: identifying the wild rivers of Australia. Landscape and Urban Planning 60, 1–25. 49. Kingsford RT (2000) Review: ecological impacts of dams, water diversions and river management on floodplain wetlands in Australia. Austral Ecology 25, 109–127. 50. ANCOLD Inc. (2002) Register of large dams in Australia (ICOLD Dam Register.xls). Australian National Committee on Large Dams Incorporated (ANCOLD Inc.). Available at: <http://www.ancold.org.au>. 51. Finlayson CM, Farrell TP and Griffiths DJ (1984) Studies of the hydrobiology of a tropical lake in north‐western Queensland III. Growth, chemical composition and potential for harvest of the aquatic vegetation. Australian Journal of Marine and Freshwater Research 35, 526–536. 52. Werren G (2000) Observations of weed infestations in the Speewah, Kuranda – Lake Southedge area from aerial inspection by helicopter. Report 00/11, June 2000. Australian Centre for Tropical Freshwater Research, James Cook University, Townsville. 53. Ryan TJ, Aland G and Cogle AL (2002) Environmental condition of the upper Mitchell River system: water quality and ecology. Report prepared for the National Heritage Trust (Ref # 962005). Queensland Department of Natural Resources and Mines and the Queensland Department of Primary Industries. 54. Saker ML and Griffiths DJ (2001) Occurrence of blooms of the cyanobacterium Cylindrospermopsis raciborskii (Wolozynnska) Seenaya and Subba Raju in a north Queensland domestic water supply. Marine and Freshwater Research 52, 907–915. 55. Trayler K, Malseed B and Brainbridge M. (2006) Environmental values, flow related issues and objectives for the lower Ord River, Western Australia. Report # EWR1, Department of Water, Perth. Aquatic ecosystems in northern Australia Chapter 3 ‐ 68
Northern Australia Land and Water Science Review full report October 2009 56. Start AN and Handasyde T (2002) Using photographs to document environmental change: the effects of dams on the riparian environment of the lower Ord River. Australian Journal of Botany 50, 465–480. 57. Cluett LJ and Radford BTM (2003) Downstream morphological change in response to dam construction: a GIS based approach for the lower Ord River, Western Australia. Water Science and Technology 48, 1–8. 58. Pettit NE, Froend RH and Davies PM (2001) Identifying the natural flow regime and the relationship with riparian vegetation for two contrasting Western Australian rivers. Regulated Rivers Research and Management 17, 201–215. 59. Lund MA and McCrea A (2002) Assessment of Ecological Risk associated with irrigation in the Ord River catchment. LWRRDC project WRC10: Report number 2001‐05. 60. Arthington AH (1996) The effects of agricultural landuse and cotton production on tributaries of the Darling River, Australia. Geo Journal 40, 115–125. 61. Yoshikane M, Winston RK, Shibata Y, et al. (2006) Very high concentrations of DDE and toxaphene residues in crocodiles from the Ord River, Western Australia: an investigation into possible endocrine disruption. Journal of Environmental Monitoring 8, 649–661. 62. Blanch S, Rea N and Scott G (2005) Aquatic conservation values of the Daly River Catchment, Northern Territory, Australia. A report prepared by WWF‐Australia, Charles Darwin University and the Environment Centre NT, Darwin. 63. Douglas MM, Bunn SE and Davies PM (2005) River and wetland food webs in Australia’s wet‐dry tropics: general principles and implications for management. Marine and Freshwater Research 56, 329–342. 64. Woinarski JCZ, Brock C, Armstrong M, et al (2000) Bird distribution in riparian vegetation in the extensive natural landscape of Australia’s tropical savanna: broad scale survey and analysis of a distributional data base. Biogeography 27, 853–868. 65. Garnett ST and Crowley GM (2000) The Action Plan for Australian Birds 2000. [Online]. Canberra, ACT: Environment Australia and Birds Australia. Available at: <http://www.environment.gov.au/biodiversity/threatened/publications/action/birds2000/index.
html>. 66. Pusey BJ and Arthington AH (2003) Importance of the riparian zone to conservation and management of freshwater fish: a review. Marine and Freshwater Research 54, 1–16. 67. Lynch RJ, Bunn SE and Catterall CP (2002) Adult aquatic insects: Potential contributors to riparian food webs in Australia's wet–dry tropics. Austral Ecology 27, 515–526. 68. Bunn SE (1993) Riparian‐stream linkages: research needs for the protection of in‐stream values. Australian Biology 6, 46–51. 69. Naiman RJ, and Decamps H (1997) The ecology of interfaces ‐ riparian zones. Annual Review of Ecology and Systematics 28, 621–658 70. Thorp JH and Delong MD (1994) The riverine productivity model: an heuristic view of carbon sources and organic processing in large river ecosystems. Oikos 70, 305–308. 71. Norris RH and Thoms MC (1999) What is river health? Freshwater Biology 41, 1–13. 72. Leigh C and Sheldon F (2009) Hydrological changes and ecological impacts associated with water resource development in large floodplain rivers in the Australian tropics. River Research and Applications 24, 1251–1270. 73. Smith MJ, Kay WR, Edward DHD, et al. (1999) AUSRIVAS: Using macroinvertebrates to assess ecological condition of rivers in Western Australia. Freshwater Biology 41, 269–282. 74. Storey AW Davies PM and Froend RH (2001) Fitzroy River System: environmental values. Report to the Water and Rivers Commission, Western Australia. 75. Cook GD and Dias L (2006) TURNER REVIEW No. 12. It was no accident: deliberate plant introductions by Australian government agencies during the 20th century. Australian Journal of Botany 54, 601–625. Aquatic ecosystems in northern Australia Chapter 3 ‐ 69
Northern Australia Land and Water Science Review full report October 2009 76. Spencer PBS and Hampton JO (2005) Illegal translocation and genetic structure of feral pigs in Western Australia. Journal of Wildlife Management 69, 377–384. 77. Webb AC (2007) Status of non‐indigenous freshwater fishes in tropical north Queensland, including establishment success, rates of spread, range and introduction pathways. Journal and Proceedings of the Royal Society of New South Wales 140, 63–78. 78. Ridpath MG (1991) Feral mammals and their environment. Pp 169–191 In: Haynes CD, Ridpath MG and Ridpath MAJ (eds.) Monsoonal Australia: landscape, ecology and man in the northern lowlands. Balkema, Rotterdam. 79. Petty AM, Werner PA, Lehmann CER, et al. (2007) Savanna responses to feral buffalo in Kakadu National Park, Australia. Ecological Monographs 77, 441–463. 80. Caley P (1997) Movements, activity patterns and habitat use of feral pigs (Sus scrofa) in a tropical habitat. Wildlife Research 24, 77–87. 81. Cowled BD, Giannni F, Beckett SD, et al. (2009) Feral figs: predicting future distributions. Wildlife Research 36, 242–251. 82. Alford RA, Brown GP, Schwarzkopf L, et al. (2009) Comparisons through time and space suggest rapid evolution of dispersal behaviour in an invasive species. Wildlife Research 36, 23–28. 83. Perna C and Burrows D (2005) Improved dissolved oxygen status following removal of exotic weed mats in important fish habitat lagoons of the tropical Burdekin River floodplain, Australia. Marine Pollution Bulletin 51, 138–148. 84. CRC Weeds (2003) CRC Weed Management Guides. Viewed 9 October 2009, <http://www.weedscrc.org.au/publications/weed_man_guides.html#bpmg>. 85. van Dam RA, Camilleri C, Bayliss P and Markich SJ (2004) Ecological risk assessment of Tebuthiuron on a tropical Australian wetland. Human and Ecological Risk Assessment 10, 1069–
1097. 86. Faulks JJ (1998) Daly River Catchment, An assessment of the physical and ecological condition of the Daly River and its major tributaries. Top End Waterways project. Technical report TR99/10 Northern Territory Department of Lands, Planning and Environment. 87. Schult J and Metcalfe R (2006) High nitrate concentrations in the Douglas River and their impact on Daly River water quality. Report No 9/2006D. Aquatic Health Unit, Department of Natural Resources, Environment and the Arts, Darwin, NT. 88. Ganf GC and Rea N (2007) Potential for algal blooms in tropical rivers of the Northern Territory, Australia. Marine and Freshwater Research 58, 315–326. 89. Moller G, Johnson DJ and Van Manen N (2002) An ecological and physical assessment of the condition of streams in the Mitchell, Lynd, Palmer, Walsh and Alice River catchments. Queensland Department of Natural Resources and Mines, Brisbane. 90. Thomson C, Marshall C, Conrick D and Choy S (2002) Impact of landuse on ecological water quality in the Mitchell River catchment, North Queensland. Freshwater Biological Monitoring Report #38, Queensland Department of Natural Resources and Mines, Brisbane. 91. Herbert BW, Peeters JA, Graham PA and Hogan AE (1995) Freshwater fishes and aquatic habitat survey of Cape York Peninsula. Natural Resources Analysis Program. Queensland Department of Primary Industries, Brisbane. 92. Brooks A, Lymburner L, Dove J, et al. (2008) Development of a riparian condition approach for the northern Gulf rivers using remote sensing and ground survey. Project GRU38 Final Report prepared for Land and Water Australia. Australian Rivers Institute, Griffith University, Brisbane. 93. Welch M, Schult J and Padovan A (2008) Effects of urban stormwater on heavy metal and nutrient concentrations in mangrove sediments of Darwin Harbour. . Report 08/2008, Aquatic Health Unit, Environment and Heritage Division, Northern Territory Department of Natural Resources Environment and Arts, Darwin. 94. Scheltinga DM, Fearon R, Bell A and Heydon L (2006) Assessment of information needs for freshwater flows into Australian estuaries. Land and Water Australia, Canberra. Aquatic ecosystems in northern Australia Chapter 3 ‐ 70
Northern Australia Land and Water Science Review full report October 2009 95. Dixon I, Douglas M, Dowe J and Burrows D (2006) Tropical Rapid Appraisal of Riparian Condition, Version 1 (for use in tropical savannas), River and Riparian Land Management. Technical Guideline No. 7. Land and Water Australia, Canberra. 96. Dowe JL (2008) Report 4: Distribution and ecological preferences of riparian vegetation in northern Australia. In: Lukacs GP and Finlayson CM (eds.) A compendium of ecological information on Australia’s northern tropical rivers. Sub‐project 1 of Australia’s tropical rivers – an integrated data assessment and analysis (DET18). A report to Land and Water Australia. National Centre for Tropical Wetland Research, Townsville, Queensland. 97. Environment Australia (2001) A directory of important wetlands in Australia, Third Edition. Environment Australia, Canberra. 98. Vörösmarty CJ, Lettenmaier D, Leveque C, et al. (2004) Humans transforming the global water system. EOS 85, 509–514. 99. Arthington AH and Pusey BJ (2003) Flow restoration and protection in Australian rivers. River Research and Applications 19, 1–19. 100. Cambray JA and Bianco PG (1998) Freshwater fish in crisis, a Blue Planet perspective. Italian Journal of Zoology 65 (Suppl.), 345–356. 101. Erskine WD, Begg GW, Jolly P, et al. (2003) Recommended environmental water requirements for the Daly River, Northern Territory, based on ecological, hydrological and biological principles. Supervising Scientist Report 175 (National River Health Program, Environmental Flows Initiative, Technical Report 4) Supervising Scientist. Darwin, NT. 102. Douglas M, Pusey B, Kennard M and Jackson S (2005) Water regime dependence of fish in the wet‐dry tropics. RipRap 29, 10–12. 103. Chan T, Hart B, Kennard, MJ, et al. (submitted) Bayesian network models for environmental flow decision‐making in the Daly River, Northern territory, Australia. River Research and Applications. 104. Kennard MJ (2006) Appendix H. Freshwater fish. In: Brizga SO, Arthington AH, Connolly R, et al. (eds.) Logan Basin Water Resource Plan (WRP) – Environmental Investigations Report. Queensland Department of Natural Resources, Mines and Water, Brisbane. 105. Matthews WJ, Gido KB and Gelwick FP (2004) Fish assemblages of reservoirs, illustrated by Lake Texoma (Oklahoma‐Texas, USA) as a representative system. North American Journal of Lake Management 20, 219–239. 106. Hydrobiology (2006) Gulf and Mitchell: ecological and geomorphological assessment for the Gulf and Mitchell Water Resource Plans. Report prepared by Hydrobiology Pty. Ltd. for the Queensland Department of Natural Resources and Mines. 107. Olden JD and Naiman RJ (2009) Incorporating thermal regimes into environmental flows assessments: modifying dam operations to restore freshwater ecosystem integrity. Freshwater Biology doi:10.1111/j.1365‐2427.2009.02179.x. 108. Preston BL and Jones RN. (2008) Screening climatic and non‐climatic risks to Australian catchments. Geog. Res. 46: 258–274. 109. CSIRO (2009) Water in northern Australia. Summary of reports to the Australian Government from the CSIRO Northern Australia Sustainable Yields Project. CSIRO, Australia. 110. Stainforth DA, Aina T, Christensen C, et al. (2005) Uncertainty in predictions of the climate response to rising levels of greenhouse gases. Nature 433, 403–406. 111. Botkin DB, Saxe H, Araujo MB, et al. (2007) Forecasting the effects of global warming on biodiversity. BioScience 57, 227–236. 112. Fausch KD, Torgersen CE, Baxter CV, et al. (2002) Landscapes to riverscapes: bridging the gap between research and conservation of stream fishes. BioScience 52, 483–498. 113. Olden JD, Kennard MJ and Pusey BJ (2008) Species invasions and the changing biogeography of Australian freshwater fishes. Global Ecology and Biogeography 17, 25–37. 114. Bates BC, Kundzewicz ZW, Wu S and Palutikof JP (eds.) (2008) Climate Change and Water. Technical Paper of the Intergovernmental Panel on Climate Change. IPCC Secretariat, Geneva. Aquatic ecosystems in northern Australia Chapter 3 ‐ 71
Northern Australia Land and Water Science Review full report October 2009 115. Chiew FHS and McMahon TA (2002) Modelling the impacts of climate change on Australian stream flow. Hydrological Processes 16, 1235–1245. 116. Meehl GA, Stocker TF, Collins WD, et al. (2007) Global climate projections. In: Solomon S, Qin D, Manning M, et al. (eds.) Climate Change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK. 117. Butler B and Burrows DW (2007) Dissolved oxygen guidelines for freshwater habitats in northern Australia. Report 07/38, Australian centre for Tropical Freshwater Research, James Cook University, Townsville. 118. Deutsch CA, Tewksbury JJ, Huey RB, et al. (2008) Impacts of climate warming on terrestrial ectotherms across latitude. Proceedings National Academy Sciences USA 105, 6668–6672. 119. Knighton AD, Mills K and Woodroffe CD (1991) Tidal creek extensions and saltwater intrusion in northern Australia. Geology 19, 831–834. 120. Finlayson CM, Eliot I and Waterman P (2002) Climate change and sea level rise in the Alligator Rivers region, northern Australia. Pp 101–106 In: Rovis‐Hermann J, Evans KG, Webb AL and Pidgeon RWJ (eds.) Environmental Research Institute of the Supervising Scientist research summary 1995‐2000. Supervising Scientist Report 166, Supervising Scientist, Darwin NT. 121. Allan JD (2004) Landscapes and riverscapes: the influence of landuse on stream ecosystems. Annual Review of Ecology and Systematics 35, 257–84. 122. Rayment GE (2003) Water quality in sugar catchments of Queensland. Water Science and Technology 48, 35–47. 123. Trimble SW and Mendel AC (1995) The cow as geomorphic agent – a critical review. Geomorphology 13, 233–253. 124. Greenwood KL and McKenzie BM (2001) Grazing effects on soil physical properties and the consequences for pastures: a review. Australian Journal of Experimental Agriculture 41, 1231–
1250. 125. Platts WS (1991) Livestock grazing. In: WR Meehan (ed.) Influences of forest and rangeland management on Salmonid fishes and their habitats. American Fisheries Society Special Publication 19, Bethesda, MD. 126. Fairfax RJ and Fensham RJ (2002) In the footsteps of J. Alfred Griffiths: a cataclysmic history of Great Artesian Basin springs in Queensland. Australian Geographical Studies 40, 210–230. 127. Payne AL, Watson IW and Novelly PE (2004) Spectacular recovery in the Ord River catchment. Miscellaneous publication (Western Australia. Dept. of Agriculture); 2004/17. South Perth, W.A. Dept. of Agriculture, 2004. 128. Jeffree RA, Twining JR and Thomson J (2001) Recovery of fish communities in the Finniss River northern Australia, following remediation of the Rum Jungle uranium/copper mine site. Environmental Science and Technology 35, 2932–2941. 129. Storrs MJ and Finlayson CM (2002) A review of wetland conservation issues in the Northern Territory. Pp 107–113 In: Rovis‐Hermann J, Evans KG, Webb AL and Pidgeon RWJ (eds.) Environmental Research Institute of the Supervising Scientist research summary 1995‐2000. Supervising Scientist Report 166, Supervising Scientist, Darwin NT. 130. Moliere DR, Evans KG, Saynor MJ and Erskine WD (2002) Suspended sediment load in the receiving catchment of the Jabiluka uranium mine site, Northern Territory. Pp 37–41 In: Rovis‐
Hermann J, Evans KG, Webb AL and Pidgeon RWJ (eds.) Environmental Research Institute of the Supervising Scientist research summary 1995‐2000. Supervising Scientist Report 166, Supervising Scientist, Darwin NT. 131. Graham MK, Hancock GR and Evans KG (2002) An erosion assessment of the former Narbelek Uranium mine, Northern Territory. Pp 48–52 In: Rovis‐Hermann J, Evans KG, Webb AL and Pidgeon RWJ (eds.) Environmental Research Institute of the Supervising Scientist research summary 1995‐2000. Supervising Scientist Report 166, Supervising Scientist, Darwin NT. Aquatic ecosystems in northern Australia Chapter 3 ‐ 72
Northern Australia Land and Water Science Review full report October 2009 132. Saynor MJ and Evans KG (2002) Sediment loss from a waste rock dump, Ranger mine, northern Australia. Pp 53–60 In: Rovis‐Hermann J, Evans KG, Webb AL and Pidgeon RWJ (eds.) Environmental Research Institute of the Supervising Scientist research summary 1995‐2000. Supervising Scientist Report 166, Supervising Scientist, Darwin NT. 133. Hadwen WL, Arthington AH and Boon PI (2008) Detecting visitor impacts in and around aquatic ecosystems within protected areas. CRC for Sustainable Tourism. 134. Hadwen WL, Arthington AH and Mosisch TD (2003) The impact of tourism on dune lakes on Fraser Island, Australia. Lakes and Reservoirs: Research and Management 8, 15–26. 135. Hart A (2002) Fisheries Monitoring Programs in the South Gulf of Carpentaria – a review. Report prepared for the Australian Centre for Tropical Freshwater Research, James cook university, Townsville. 136. Thorburn DC, Morgan DL, Rowland AJ and Gill H (2004) Elasmobranchs in the Fitzroy River, Western Australia. Report prepared by the Centre for Fish and Fisheries Research, Murdoch University for the Natural Heritage Trust. 137. McPhee D, Leadbitter D and Skilleter GA (2002) Swallowing the bait: Is recreational fishing in Australia ecologically sustainable? Pacific Conservation Biology 8, 40–51. 138. Cooke SJ and Cowx IG (2004) The Role of Recreational Fishing in Global Fish Crises. BioScience 54, 857–859. 139. Bartholomew A and Bohnsack J (2005) A review of catch‐and‐release angling mortality with implications for no‐take reserves. Reviews in Fish Biology and Fisheries 15, 129–154. 140. Mosisch TD and Arthington AH (2004) Impacts of recreational power boating on freshwater ecosystems. Chapter 8, In: R Buckley (ed.) Environmental Impacts of Ecotourism. CABI Publishing Wallingford, Oxfordshire. 141. Mosisch TD and Arthington AH (2001) Polycyclic aromatic hydrocarbon residues in the sediments of a dune lake as a result of power boating. Lakes and Reservoirs: Research and Management 6, 21–32. 142. Endler JA and Thery M (1996) Interacting effects of lek placement, display behaviour and color patterns in three Neotropical forest‐dwelling birds. The American Naturalist 148, 421–452. 143. von May R and Donnelly MA (2009) Do trails affect relative abundance estimates of rainforest frogs and lizards? Austral Ecology 34, 613–620. 144. Hadwen WL and Bunn SE (2004) Tourists increase the contribution of authochthonous carbon to littoral zone foodwebs in oligotrophic dune lakes. Marine and Freshwater Research 55, 701–708. 145. Hadwen WL and Bunn SE (2005) Foodweb responses to low level nutrient and 15N tracer additions in the littoral zone of an oligotrophic dune lake. Limnology and Oceanography 50, 1096–1105. 146. McJannet DL, Wallace JW, Henderson A and McMahon J (2009) High and low flow regime changes at environmental assets across northern Australia under future climate and development scenarios. A report to the Australian Government from the CSIRO Northern Australian Sustainable Yields Project. CSIRO Water for a Healthy Country National Research Flagship, Division of Land and Water, Canberra. In prep. 147. Morgan D, Thorburn D, Fenton J, et al. (2005) Influence of the Camballin Barrage on fish communities in the Fitzroy River, Western Australia. Murdoch University/Kimberley Land Council/Department of Environment report to Land and Water Australia. 148. Arthington AH and Pusey BJ (1993) In‐stream flow management in Australia: methods, deficiencies and future directions. In Arthington AH (ed.) Water: an endangered national resource. Australian Biologist 6, 52–60. 149. Brizga SO, Arthington AH, Balcombe S, et al. (2005) Mary Basin draft Water Resource Plan: Environmental flow assessment framework and scenario implications. Queensland Department of Natural Resources and Mines, QNRM05341. 150. Blanch S (2008) Steps to a sustainable Northern Australia. Ecological Management and Restoration 9, 110–115. Aquatic ecosystems in northern Australia Chapter 3 ‐ 73