Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
LAKE CARGELLIGO – ENVIRONMENTAL VALUES The Lake Cargelligo system is made up of a number of different ecological components which add to its value as a wetland. The main ecological components include: Open Water areas (eg. Curlew Water and the front recreation area of Lake Cargelligo) River Red Gum Swamps (eg. the back area of Lake Cargelligo) Black Box Woodlands (eg. located between Lake Cargelligo and the Lachlan River) Reed Beds (eg. located in the back area of Lake Cargelligo) Mudflat areas (eg. Sheet of Water, McInnes Basin and Lake Cargelligo); Lignum Swamps (eg. back area of Lake Cargelligo) Permanent River Channel (Lachlan River). The characteristics and functions of these assets are described below. Open Water There are two significant open water lakes in the Lake Cargelligo system. Curlew Water and the front recreational area of Lake Cargelligo provide open water habitats to 3-6 m in depth. Under normal conditions, both lakes are filled by the delivery of river water via the inlet channel, with water first flowing through Curlew Water, via Sheet of Water, and then onto the main lake. Throughout the history of regulation, both these areas have generally remained permanently inundated, however, under severe drought conditions, they may be drawn-down to dead storage levels. These areas provide important habitat for large bodied fish species and waterbirds and, as they tend to be more permanent water bodies within a variable landscape, they can provide drought refuge for a variety of plant and animal species. Open water areas, or pelagic zones, can be divided into the euphotic zone, measured from the surface to where light ceases to penetrate, and the profundal zone, where light does not penetrate. Algae tend to dominate in the euphotic zone, where light penetrates, and provide food for zooplankton and fish. The benthic zone, or lake bottom, also provides food and habitat through sediments and accumulated detrital material. River Red Gum Swamps Swamps occur throughout the floodplain of the lower Lachlan and are often distinguished by the presence of forest or woodland, generally dominated by river red gum (Eucalyptus camaldulensis). River red gum woodlands provide important functions for the lower Lachlan as they encourage the growth of understorey plants, largely through shading, and supply habitat and food for many animal species. Riparian river red gums also influence nearby aquatic areas through shading and by inputs of litter and woody debris. River red gum woodland also influences water flow and aids channel stability. River red gums tend to occur along the margins of channels and at higher elevations than reed beds. While mature trees can tolerate prolonged flooding (up to 4 years), seedlings are less tolerant, particularly if they are completely submerged for more than a few weeks. For this reason, it is generally thought that a flooding frequency of once every one to three years and inundation periods of 4-7 months is ideal to maintain the health of mature trees, support successful regeneration and limit encroachment by other vegetation types. Changes to hydrology are likely to impact on the health, distribution and extent of river red gums. Over the last few years of drought it is likely that reduced water availability has led to the decline in river red gum health and recruitment. Changes to grazing regimes can also influence the long term health and extent of these communities, particularly by reducing recruitment success. Red gums are also harvested throughout the lower Lachlan. Black Box Woodlands Black box (Eucalyptus largiflorens) woodlands tend to be less dense and age diverse than that of river red gum forests. The understorey of black box woodlands are often dominated by a high diversity of chenopod shrubs including old man saltbush (Atriplex nummularia), nitre goosefoot (Chenopodium nitrariaceum), curious saltbush (Dissocarpus paradoxus), ruby saltbush (Enchylaena tomentosa), black bluebush (Maireana pyramidata), creeping saltbush (Rhagodia spinesens) and Sclerolaena spp (eg. Roly-Poly). Like reed beds and river red gum swamps, black box distributions are controlled by flow patterns. They are more tolerant of water stress than river red gums and less tolerant of long periods of flooding. Black box woodlands are therefore found in more elevated areas and appear to be better suited to areas with flood frequencies of one in three to one in five years, with a wetting period of two to four months. Black box woodlands provide a habitat for understorey plants and terrestrial animals but have less interaction with aquatic communities as they are less frequently flooded and are usually a greater distance from river channels. As mature black box trees have a greater resistance to drought, they have a greater ability to survive reduced water availability frequentlyly experienced in the lower Lachlan. Reed Beds Common reed (Phragmites australis) is one of the dominant aquatic species in the lower Lachlan. Reed beds are absent from the deeper areas of the lake system where other aquatic macrophytes such as Typha and ribbon weed may dominate. The upper limit of Phragmites distribution varies with flood history, and their distribution will expand and contract in response to water availability. However, as Phragmites most commonly re-establishes via growth from rhizomes rather than seed, re-establishment following drying may take some time. Expansion is most rapid when flooding occurs early in the growing season. Reed dominated areas are productive and contribute to primary productivity within a system directly through their own growth or indirectly by providing substrate for attached algae. Reeds also reduce flow velocity, thereby reducing available nutrients and turbidity in the water column. Reed beds also provide habitat for aquatic animals, as they are structurally complex and reduce water turbulence, making them important nursery areas for fish by providing protection from predation and strong currents. Reed beds also provide feeding and breeding habitat for waterbirds, particularly following large floods. These areas are commonly used by Australasian bittern, spoonbills and ibis. They also provide pasture for cattle and are known to help recharge groundwater systems. This recharge service provides a mechanism for the export of salts that may otherwise accumulate in soils as a result of evaporation. Reed beds also reduce erosion through lowering flow velocity and binding sediments. Threatening processes such as grazing, deteriorating water quality (eg. salinity) and burning have the potential to reduce the extent of this community and perhaps accelerate any changes occurring in response to hydrological change. Mudflats Mudflats are unvegetated areas in shallow or receding waters, which increase in occurrence during the wetland’s drying phase. These areas support high levels of production by benthic micro-algae (eg. diatoms) and invertebrates, nutrient regeneration, decomposition of organic matter, thereby providing feeding habitat for wading birds. The primary production of shallow-water algae that lives on the sediment, has been found to equal that of the overlying water column, indicating that it plays an important role in keeping wetlands productive. Micro-algae are also crucial to nutrient cycling, particularly carbon cycling and are important in maintaining sediment stability. Some of the migratory waders known to utilise Lake Cargelligo wetlands, particularly the mudflats, include the red-necked stint, curlew sandpiper, pectoral sandpiper, sharp-tailed sandpiper, Latham’s snipe, painted snipe, bar-tailed godwit and black-tailed godwit. Lignum Swamps Lignum (Muehlenbeckia florulenta) occurs both as an understorey plant in open woodlands and as the dominant species in small patches of shrubland near water-ponding areas. These shrublands can be particularly important for waterbird breeding following flooding. During dry periods, few understorey species may be present in areas of lignum swamps. Those that have been recorded include branching groundsel (Senecio cunninghamii), Medic (Medicago spp.) and canary-grass (Phalaris paradoxa). Understorey diversity and abundance is likely to be significantly greater, however, following flooding of these communities. Lignum communities appear to tolerate longer dry periods and respond more quickly to wetting than other communities such as reed beds, and are capable of withstanding longer periods of flooding than river red gum. Lignum areas are particularly important for breeding amongst straw-necked ibis and glossy ibis and provides habitat for aquatic fauna during wet periods and other terrestrial fauna during dry times. Change resulting from water resource development or climate change would be expected to alter the distribution of lignum as an understorey species in river red gum woodlands, where reduced flooding frequency may result in the replacement of lignum by saltbush and other chenopods as often found associated with black box woodlands. Permanent River Channel The lower reaches of the Lachlan River contain a variety of habitat types including pools, riffles, gravel beds and some sand beds. The channel has an extremely low gradient and greatly meanders. The Lachlan below Wyangala Dam has been declared an Endangered Ecological Community (DPI 2005) and many features of the riverine system have been identified as having high conservation value. Endangered Ecological Community It should be noted that the lower Lachlan River is currently listed as an endangered ecological community. This includes all fish and aquatic invertebrates within all natural rivers, creeks, streams and associated lagoons, billabongs, lakes, wetlands, paleochannels, floodrunners, effluent streams and the floodplains of the Lachlan River, including Lake Cargelligo.