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ECOLOGICAL EFFECTS OF REDUCING STREAM BASEFLOWS FINAL REPORT August 2005 Amara Barlow, Richard Norris and Sue Nichols Report to Environment ACT Prepared by Institute for Applied Ecology University of Canberra Ecological effects of reducing stream baseflows TABLE OF CONTENTS 1 Project Details ............................................................................................................... 3 Project Title Project Staff Project Duration Project Objectives 3 3 3 3 2 Background information .............................................................................................. 4 3 Introduction................................................................................................................... 5 4 Methods ......................................................................................................................... 5 4.1 5 The 8-step MLLE framework ................................................................................ 5 Results .......................................................................................................................... 6 Step 1. Describe the characteristics of the human activity Step 2. Describe the characteristics of the investigation location Step 3. Develop a conceptual model Step 4. Relevant lines of evidence Step 5. Conduct the literature review Step 6. Refine conceptual model Step 7. Catalogue and weight the evidence Step 8. What is the verdict? 6 7 6 7 9 13 13 14 14 17 Issues – Baseflow reduction ...................................................................................... 18 6.1 Severity ............................................................................................................. 18 6.2 Extent ................................................................................................................ 19 6.3 Frequency and duration ..................................................................................... 19 6.4 Timing................................................................................................................ 20 Issues – Stream characteristics ................................................................................ 21 7.1 River enrichment ............................................................................................... 21 7.2 Position in the stream channel network.............................................................. 21 7.3 Proximity of boreholes ....................................................................................... 22 Conclusions ....................................................................................................................... 23 7.4 Overall conclusions............................................................................................ 23 7.5 Information gaps ................................................................................................ 23 7.6 Managing in the presence of knowledge gaps ................................................... 24 8 References .................................................................................................................. 24 9 Acknowledgements .................................................................................................... 25 10 Glossary ........................................................................................................... 25 ii Ecological effects of reducing stream baseflows Table of Figures Figure 1. Steps in applying MLLE (Norris et al. 2005) ............................................................ 6 Figure 2a. Wet period .......................................................................................................... 10 Figure 2b. Dry period ........................................................................................................... 11 Figure 2c. Dry period with bores .......................................................................................... 12 Figure 2d. Dry period with lots of bores ................................................................................ 13 List of Tables Table 1. ACT controlled water resources as at July 2004 (Environment ACT 2004)............... 7 Table 2. Weights applied to study types and control/reference and impact sites .................. 15 Table 3. Scheme for categorizing the importance of studies ................................................ 16 Table 4. Example of biological response and dose response weighting by study quality (Norris et al. 2005). ....................................................................................................... 16 Table 5. Effects catalog for a reduction of baseflow on lines of evidence from aquatic ecosystems. .................................................................................................................. 16 Table 6. Levels of evidence catalogue for a reduction of baseflow on lines of evidence from aquatic ecosystems. ..................................................................................................... 17 iii Ecological effects of reducing stream baseflows Executive Summary The Groundwater Study (Ecological Effects of Reducing Stream Baseflows) was undertaken by the Institute for Applied Ecology, University of Canberra. The aim of the study was to establish whether there is an impact on aquatic ecosystems by reducing baseflow in the manner caused by groundwater abstraction. The study also considers how much could baseflow be reduced without compromising stream aquatic ecosystems; and whether the effects of baseflow reduction would be stream dependent. The Multiple Lines and Levels of Evidence (MLLE) literature analysis shows expected effects of reductions in baseflow on macroinvertebrates but not on other lines of evidence. Therefore, it is clear from the literature that reductions in baseflows will have a negative ecological effect. This will be most easily demonstrated by studying macroinvertebrates but we would need very well designed local studies to demonstrate an effect on fish, algae, macrophytes or riparian vegetation. Issues that are likely to influence the ecological effects of baseflow reduction include: Severity of abstraction and low flows (e.g. cease to flow); Extent of low flows (e.g. how much of the catchment is affected?); Frequency and duration of low flow events; and Timing of low flow events. 10% groundwater abstractions are likely to have little effect on aquatic ecosystems, because groundwater modeling by Evans et al. (2005) indicates little change to the frequency of no flow events; and small changes have been shown in the literature to be of little concern. Whereas, pumping at 20% of annual recharge results in quite marked changes in the flow duration (Evan et al. 2005) and is likely to have a negative ecological effect. Ecological effects will be most severe during dry periods when baseflow is controlled by groundwater for up to >80% of the time (e.g. Sullivans Ck), but this may be catchment dependent (Evans et al. 2005). Abstractions in wet or dry years will have the same effect in dry years because of the lag time for groundwater to get to the stream. Therefore, it is not possible to manage dry and wet years independently, and so abstraction should be controlled for all years at a level that will be sustainable during dry years. The effects of abstractions will, in part, be determined by: River enrichment; Position in the stream channel network (upland vs lowland reaches); and Proximity of boreholes (distance from stream edge). Abstractions will have more effect on highly nutrient enriched rivers and rivers in the upper parts of catchments. If the bores are located close to the stream, the faster the impact of abstractions and the quicker the time to full impact, but also the quicker recovery time. At a distance of 500 metres from the stream the full impact of one year of pumping is effectively detected within about 5 years, whereas, the full impact of extraction for one year at 2 km is ongoing for considerable time (Evans et al. 2005). The quality and quantity of groundwater resources may be constantly changing, and there are many gaps in the knowledge of groundwater resources and the effects of groundwater use. 1 Ecological effects of reducing stream baseflows Therefore, an adaptive management approach is recommended based on studies designed to assess the outcomes of management decisions and inform new decisions. 2 Ecological effects of reducing stream baseflows 1 Project Details Project Title Ecological effects of reducing stream baseflows in the ACT Project Staff Leader: Prof. Richard Norris Project officers: Amara Barlow, Sue Nichols Project Duration May 2005 to 22 August 2005 Project Objectives The project objectives were to determine: 1. Is there an impact on aquatic ecosystems by reducing baseflow in the manner caused by groundwater abstraction? 2. How much could baseflow be reduced without compromising stream aquatic ecosystems? 3. Would the answer to the question above be stream dependent or is it possible to draw some general conclusions? This report has been divided into three parts to address each of the project objectives individually. 3 Ecological effects of reducing stream baseflows 2 Background information ACT Government is interested in refining the current environmental flow guideline for abstraction from groundwater. Groundwater abstraction limits of 10% of recharge were adopted in the 1999 Environmental Flow Guidelines and have followed through as being an educated but precautionary abstraction approach to take. This guideline value is based on advice from Ray Evans et al. (2004) regarding the shallow fractured rock aquifers in the ACT and the recharge that eventually discharges from the aquifer in the sub-catchment. This discharge is believed to comprise a major proportion of the baseflow in our rivers and streams. In consequence of the above points, abstraction from an aquifer will result in reduction of baseflow in streams downstream of the abstraction site (such as groundwater bores). The Guidelines recognize that periods of low flow (e.g. baseflow) are periods when aquatic ecosystems are under some stress, and reducing the baseflow further should not exacerbate this. Therefore, to protect the aquatic ecosystems groundwater abstraction should be limited to provide protection of stream baseflows. Currently, abstraction is limited to 10% of recharge as a conservative measure. The purpose of this study is to answers questions regarding the ecological response of streams to groundwater abstraction. It is well appreciated that many streams from the Great Dividing Range in South-Eastern Australia are baseflow streams and are highly dependent on groundwater discharge (Hatton and Evans 1998). However, groundwater movement is unseen and poorly understood. Exploitation of groundwater resources for irrigation, public water supply and many other uses, has the potential to significantly alter groundwater levels and groundwater behaviour. In addition, many land use practices also change groundwater behaviour. These groundwater processes, may influence the health of aquatic ecosystems (Hatton and Evans 1998). In aquatic ecosystems highly dependent on groundwater, moderate changes to groundwater discharge or water tables would lead to substantial decreases in the extent, severity and frequency of drying, or ceasing to flow. Such changes may markedly affect the health of these aquatic ecosystems. There are some baseflow systems of the South-Eastern uplands that are highly dependent on groundwater (Hatton and Evans 1998). For a number of aquatic systems (streams and wetlands), it is likely that a unit change in the amount of groundwater will result in a proportional change in the health of those ecosystems. In other words, were groundwater discharge cut by half, one might expect some equivalent diminution of the ecosystem. Some base-flow systems of the South-Eastern uplands are proportionally dependent on groundwater (Hatton and Evans 1998). Aquatic ecosystem dependence is not solely related to the amount of baseflow, but variability and predictability of flow are likely to be important. Generally, if there is baseflow, then ecosystems will tend to be more dependent and vulnerable in lower rainfall zones, and where this baseflow arises from porous media aquifer systems (Hatton and Evans 1998). There is limited groundwater data for the Canberra region and also limited information on the relationships between baseflow conditions and the aquatic ecosystem responses. For the purposes of this report we have used the available local information on groundwater aquatic ecosystems and combined this with a rigorous assessment of the scientific literature. The scientific literature has been incorporated into a quantitative framework known as Multiple Levels and Lines of Evidence (Norris et al. 2005). 4 Ecological effects of reducing stream baseflows Part 1 – Impacts of groundwater abstraction 3 Introduction Groundwater abstraction reduces baseflows (Evans et al. 2005); and it could be reasonably expected that the effects would be most apparent in dry years, when baseflow dominates streamflow. Further, the effects of groundwater abstraction would be likely to be seen first in the upper parts of catchments that would tend to dry out first and where abstraction is in close proximity to rivers or wetlands. Therefore, the possible effects have been dealt with for upper and lower catchments and considered the aquatic ecological effects of: • Extent of drying or cease to flow; • Severity and; • Frequency of events. 4 Methods 4.1 The 8-step MLLE framework The eight step MLLE framework (Fig.1) adapted by Norris et al. (2005) from Downes et al. (2002) was used to conduct the literature review of reduced stream baseflow. The review included international literature, Australian literature and local unpublished data. Several studies suggest that artificially-induced low flows and natural droughts can have similar consequences on lotic ecosystems (McIntosh et al. 2002; Suren et al. 2003). However, Smakhtin (2001) in a review of low flow hydrology suggests that natural factors, which influence the low-flow regime of the river and human effects on these processes, should be considered separately. A comparison of the MLLE outputs was conducted to determine whether the inclusion of the natural drought literature produced similar results to literature that considered human influence on low flows. There was little difference in the MLLE outputs, with the exception of macroinvertebrate taxa richness or diversity. Macroinvertebrates may be adapted to naturally occurring low flows, therefore, the decision was made not to include the natural drought literature. 5 Ecological effects of reducing stream baseflows 1. Characteristics of the human activity Question(s) 2. Characteristics of location Question(s) 3. Conceptual model 6. Additional lines of evidence 4. Relevant lines of evidence 5. Literature review 7. Catalogue & weight the evidence (local data & literature) Can be done using the MLLE software) 8. The verdict Figure 1. Steps in applying MLLE (Norris et al. 2005) 5 Results Step 1. Describe the characteristics of the human activity The human activity of concern is groundwater abstraction. In many regions groundwater and surface water resources are connected, and most surface water features (rivers, lakes, dams, wetlands) generally interact with groundwater. The exploitation of, or quality of one resource, can therefore affect the other (Ivkovic et al. 2004). Rivers generally interact with groundwater in three basic ways: streams gain water from inflow of ground water through the streambed (gaining stream), they lose water to ground water by outflow through the streambed (losing stream), or they do both, gaining in some reaches and losing in other reaches (Ivkovic et al. 2004). However, while this relationship is obviously linear, the spatial and temporal effects may not be so because of features such as stream gradient, upstream/downstream location and proximity to the aquatic systems, especially sensitive ones such as wetlands. Surface water bodies within the ACT are classified as gaining streams, determined from 8 groundwater desktop studies conducted by iCAM in 2004. Abstraction from an aquifer (such as through groundwater bores) may result in reduction of baseflow in streams downstream of the abstraction site. Whenever a megalitre of groundwater is extracted via a pumped bore, a megalitre of groundwater is lost from some other part of the aquifer system (Evans et al. 2004). The ACT Environmental Flow Guidelines recognize that periods of low flow (e.g. baseflow) are periods when aquatic ecosystems are under some stress, and reducing the baseflow further would exacerbate this (Environment ACT 2004). 6 Ecological effects of reducing stream baseflows Evans et al. (2004) suggest that it is likely that the drawdown associated with groundwater pumping in the Woden Sub-Catchment has reduced the baseflows in the nearby creeks. The impact of groundwater extraction may result in an increase in groundwater salinity because of increased hydraulic gradients drawing in more saline groundwater. Consideration should be given to limiting groundwater withdrawals in areas where groundwater salinities have been shown to be increasing over a time span of several years. This will require specific changes to licence conditions (Evans et al. 2004). The response time for groundwater pumping to impact river flows in a hydraulically connected groundwater-river system is a function of the aquifer diffusivity (expressed as the ratio of aquifer transmissivity to storativity) and the distance of the bore to the river. Commonly, the natural hydraulic connection between river and aquifer is exploited by near-river installation of wells designed to draw down groundwater levels below the river level and induce recharge by surface water. Once a bore’s pumping is balanced by stream depletion, the water allocation arguably becomes a surface water allocation (Ivkovic et al. 2004). Step 2. Describe the characteristics of the investigation location The investigation location is the Australian Capital Territory (ACT), which lies within the Upper Murrumbidgee Catchment. For the most part groundwater in the ACT is in shallow aquifers in the joints of the bedrock (a fractured rock aquifer). These aquifers tend to be shallow (generally less than 100 m deep), and the water from them varies in quality from good to saline, and also in yield. With this sort of shallow aquifer, rainfall percolates through the soil into the aquifer, travels through the aquifer and discharges back to the surface, usually into streams at the bottom of valleys. The low flow in smaller streams is largely made up of this discharge except during rainfall events (ACT Government 2004). Any reduction in discharge from the aquifer would result in a reduction in the low flows in the stream (ACT Government 2004). Consequently, if there is over abstraction from groundwater in a sub-catchment, streams that used to flow may cease to flow and dry up causing a significant impact on the health of the stream. In the ACT Environmental Flow Guidelines groundwater abstraction is limited to 10 per cent of recharge to ensure that there is no significant impact on streams during periods of low flow (ACT Government 2004). There are 32 separate management units or subcatchments in the ACT (Table 1). Subcatchments in which the ACT has an interest are those within the ACT, water supply catchments upstream of Googong Dam, and those that flow into or through the ACT (Environment ACT 2004). Table 1. ACT controlled water resources as at July 2004 (Environment ACT 2004) Catchment Subcatchment number Sub-catchment name ACT Environment Allocation (ML) ACT controlled groundwater Available for Use (ML) Murrumbidgee and tributaries 1 Michelago 2314 100 2 Tharwa 8806 250 3 Kambah 6643 173 4 Uriarra 15580 180 5 Woodstock 1225 30 7 Ecological effects of reducing stream baseflows 6 Guises 1935 76 7 Naas 35619 950 8 Gudgenby 46569 1300 9 Tennent 6884 150 10 Corin 19283 950 11 Bendora 9533 500 12 Lower Cotter 9342 600 13 Paddys 36571 1010 Tuggeranong Ck and tributaries 14 Tuggeranong 7193 60 Molonglo and tributaries 15 Upper Molonglo 1160 34 16 Kowen 4896 160 17 Fyshwick 1712 68 18 Jerrabomberra Headwaters 0 0 19 Jerrabomberra 4236 240 20 Lake Burley Griffin 5116 68 21 Coppins 4832 119 22 Woolshed 2173 64 23 Sullivans 5726 73 24 Woden 6191 56 25 Weston 3628 24 26 Tinderry 7571 0 27 Googong 784 0 28 Lower Queanbeyan 20 0 29 Burra 1077 0 30 Gungahlin 4727 80 31 Lake Ginninderra 5456 50 32 Parkwood 5150 90 Gudgenby and tributaries Cotter and tributaries Queanbeyan and tributaries Ginninderra Ck and tributaries Groundwater reserves in the ACT are not large and are contained within confined fractured rock aquifers with yields generally less than 1.0 litre per second. In addition, salinity levels can be -1 high (over 1,000 mg L of total dissolved salts). Hence only limited use of groundwater occurs relative to Murray-Darling Basin use, but within the ACT there are several subcatchments in which the volume of water available for groundwater use has been fully licenced. While there have been a number of desktop studies undertaken on aquifers within various subcatchments, limited field analysis has been undertaken into the actual performance of particular ACT aquifers. The amount of groundwater available for extraction from each sub-catchment is limited to 10 per cent of groundwater recharge until research on a specific sub-catchment determines that a higher level of groundwater use is sustainable (Environment ACT 2004). 8 Ecological effects of reducing stream baseflows Groundwater recharge is the entry of water into the saturated zone or water table and the associated flow away from the entry point within the saturated zone. Any assessment of recharge must be based on long-term data because of the slow recharge rates of most aquifers (Environment ACT 2004). There are many other potential sources of impact on aquatic ecosystems in the ACT: Urban water may contribute to groundwater recharge, therefore, some subcatchments may have higher than natural groundwater levels and baseflow. River regulation (for drinking water supply, and recreational use) may already be causing unnatural low flows in some river systems. Step 3. Develop a conceptual model During a wet period, the contribution of groundwater flow to the river is not critical to the aquatic ecosystem because surface water (overland) contributes much larger volumes to the flow (Figure 2a). However, abstractions during wet times may still affect dry weather flow because of the lag time for groundwater to reach the stream and contribute to baseflow. During a dry period, the contribution of groundwater flow to the river is critical to the maintenance of the aquatic ecosystem because of the loss of surface water (overland) flow (Figure 2b). During a dry period, groundwater abstraction may lower flow levels and result in drying of the channel and longitudinal fragmentation of the stream into pools (isolated pools provide refugia for aquatic organisms) (Figure 2c). During a dry period, extensive groundwater abstraction may lower flow levels to the point where the river ceases to flow and the hyporheos also becomes dry (Figure 2d). 9 Ecological effects of reducing stream baseflows Figure 2a. Wet period 10 Ecological effects of reducing stream baseflows Figure 2b. Dry period 11 Ecological effects of reducing stream baseflows Figure 2c. Dry period with bores 12 Ecological effects of reducing stream baseflows Figure 2d. Dry period with lots of bores Step 4. Relevant lines of evidence The lines of evidence considered in this study were: Change in fish community; Change in algae; Change in riparian condition; Change in macrophytes; Decrease in macroinvertebrate taxa richness or diversity; Decrease in macroinvertebrate abundance or density; and Change in macroinvertebrate community composition. Step 5. Conduct the literature review The databases used to search for articles were Cambridge Scientific Abstracts, Firstsearch, and Web of Knowledge. The following keywords were entered as search terms: Groundwater, river, stream, abstraction, baseflow, low flow, reduced flow, drought, surface-groundwater relations, Australia. A total of 63 articles were collected and reviewed in the initial literature scan, 20 of which were considered comparable to the current study and included in the MLLE assessment (Appendix A). 13 Ecological effects of reducing stream baseflows Step 6. Refine conceptual model There was little information on stream baseflow reduction, therefore, the literature review looked at flow reduction in general, rather than just baseflow reduction. The literature review revealed many potential impacts of instream flow reduction, including: Increased sedimentation; Changes to the morphology of the stream channel and floodplain; Changes to the distribution and abundance of stream biota; Exacerbate the effects of water pollution; Increased water temperatures during low-flow periods; Reducing overbank flooding; Changes in the density, productivity, and species composition of wetland and riparian vegetation; Changes in the relative abundance of algae, allochthonous material and organics; Changes in aquatic habitat; Adverse water quality effects; Decreased food availability, depending on the species and functional feeding group; Species that are immobile or slow may lack the ability to adjust to reduced water levels; therefore, allowing more mobile organisms to become the established dominant species; Changes to the inter- and intra-specific interactions within the disturbed ecosystem; Physical and chemical processes (e.g. temperature, dissolved oxygen) can deviate from normal conditions (Smakhtin 2001; McIntosh et al. 2002). Step 7. Catalogue and weight the evidence The schema of Norris et al. (2005) was followed for weighting and cataloguing the evidence from the literature review. To catalogue each line of evidence (LOE), the number and the importance of studies was recorded against the different levels of evidence. The levels of evidence that we recorded were adapted from Downes et al. (2002) and include: ‘biological plausibility’ - absorbed into the conceptual models and noted above to indicate ecologically relevant LOEs, rather than kept as a line of evidence itself; ‘presence of a biological response’ – a recasting of the ‘experimental evidence’ level but including evidence from all types of study including experimental and observational studies; ‘evidence of a dose response relationship with the stressor’ ‘consistency of association’ – consistent spatial and temporal association of stressor and biological response. The formal procedure developed by Norris et al. (2005) for weighting the quality of papers based on the type of study design and the number of control/reference sites and the number of 14 Ecological effects of reducing stream baseflows impact sites (Table 2) was adopted. These were then combined to weight the levels of evidence; a step necessary for environmental studies. Studies in which error terms are well controlled (e.g. BACI designs) should exert greater influence than less rigorously controlled designs (e.g. only impact sites sampled). Having a control or reference brings an improvement in inferential power. There is some increase in inferential power from having more than one control. A larger number of control locations adds weight because it better estimates the envelope of ‘normal’ location behaviour (Downes et al., 2002) so that departure from ‘normal’ can be detected with more confidence. More impact locations leads to a better estimate of the range of ecological outcomes and stronger comparisons with control/reference conditions with which they are compared. An overall study weight was derived by summing each of the three categories (Table 2, 3) following a set of rules (Table 4). These weights were then converted into quality categories (High or Low) with the advantage that they more immediately relay the importance of the study than a numerical value. An example of how the number of High and Low quality studies are combined is shown in Table 4. The overall study weight for a high quality study ranges between 5 and 10 (Table 3). The overall study weight for a low quality study ranges between 1 and 4 (Table 3). The example shows the sum of the median quantitative study weights (7.5 = High quality study weight; 2.5 = Low quality study weight) (Table 4). Combinations of high and low quality studies with a median study weight of 20 or more are deemed to have a high level of support from the literature (and accompanying studies) causal criteria. A line of evidence with a median study weight of less than 20 has a low level of evidence for the ‘biological response’ and ‘dose response’ causal criteria (Tables 3, 4). Table 2. Weights applied to study types and control/reference and impact sites Study design type Weight After impact only 1 Reference/Control vs impact no before 2 Before vs after no reference/control 2 Gradient response model 3 BACI or BARI MBACI or Beyond MBACI 4 Number of reference/control sites 0 0 1 2 >2 3 Number of impact locations 1 0 2 2 >2 3 15 Ecological effects of reducing stream baseflows Table 3. Scheme for categorizing the importance of studies Overall study weight Study importance category 5-10 High 1-4 Low Table 4. Example of biological response and dose response weighting by study quality (Norris et al. 2005). Number of Low quality studies showing support Number of High quality studies showing support Sum of the Median Conclusion – Quantitative study weights evidence for causal (7.5 = Median high quality study criterion weight; 2.5 = Median low quality study weight) Biological response and dose response 0 AND 3 (0 x 2.5) + (3 x 7.5) = 22.5 High 2 AND 2 (2 x 2.5) + (2 x 7.5) = 20 High 5 AND 1 (5 x 2.5) + (1 x 7.5) = 20 High 8 AND 0 (8 x 2.5) + (0 x 2.5) = 20 High 4 AND 1 (4 x 2.5) + (1 x 7.5) = 17.5 Low 1 AND 2 (1 x 2.5) + (2 x 7.5) = 17.5 Low 7 AND 0 (7 x 2.5) + (0 x 7.5) = 17.5 Low <2 AND 2 High <5 AND 1 High <8 AND 0 High >= 0 AND >2 Low >=2 AND 2 Low >=5 AND 1 Low >=8 AND >= 0 Low Consistency Table 5. Effects catalog for a reduction of baseflow on lines of evidence from aquatic ecosystems. RespEvid = Evidence of a biological response (higher number is better), doseEvid = Evidence of a dose response (higher number is better), conEvid = Consistency among studies (low number is better). Line of evidence respEvid doseEvid conEvid Change in fish community 11 1 0 Change in algae 8 0 5 Change in riparian condition 2 0 0 Change in macrophytes 9 0 0 Decrease in macroinvertebrate taxa richness or diversity 32 8 8 Decrease in macroinvertebrate abundance or density 36 8 12 Change in macroinvertebrate community composition 43 0 24 16 Ecological effects of reducing stream baseflows Step 8. What is the verdict? Although there was insufficient evidence to confidently determine whether reduced stream baseflow causes a change in fish, algae, riparian or macrophyte communities, the majority of studies analysed found an adverse impact on the aquatic ecosystem represented by these lines of evidence (Table 4). There was support for the hypothesis that reduced stream flows cause a decrease in macroinvertebrate taxa richness or diversity; and a decrease in macroinvertebrate abundance or density (Tables 4 and 5). However, the results were inconsistent in regard to whether reduced flow changes macroinvertebrate community composition (Tables 4 and 5). Table 6. Levels of evidence catalogue for a reduction of baseflow on lines of evidence from aquatic ecosystems. Line of evidence Biological response Dose response Consistency Conclusion Change in fish community Low Low High Insufficient evidence Change in algae Low Low High Insufficient evidence Change in riparian condition Low Low High Insufficient evidence Change in macrophytes Low Low High Insufficient evidence Decrease in macroinvertebrate taxa richness or diversity High Low High Support for hypothesis Decrease in macroinvertebrate abundance or density High Low High Support for hypothesis Change in macroinvertebrate community composition High Low Low Inconsistent results In conclusion, reduction in baseflow may have effects on fish, algae, riparian condition, macrophytes and invertebrate composition but the evidence from the literature is weak or inconclusive. However, there is strong and consistent evidence that macroinvertebrate abundance and richness are negatively affected. These organisms are an important component of aquatic ecosystems and used extensively as indicators throughout the world. Therefore, we can conclude that reduction in baseflow will have an adverse effect on an important indicator of the health of aquatic ecosystems. 17 Ecological effects of reducing stream baseflows Part 2 – How much could baseflow be reduced? 6 Issues – Baseflow reduction Issues that are likely to influence the ecological effects of baseflow reduction include: Severity of abstraction and low flows (e.g. cease to flow); Extent of low flows (e.g. how much of the catchment is affected?); Frequency and duration of low flow events; and Timing of low flow events. 6.1 Severity The severity of groundwater abstraction may vary depending on the reliance of streams on groundwater discharge and the other contributions to stream flow from surface water. Thresholds that may cause stream degradation include: increased low flow levels; drying of the channel; longitudinal fragmentation of the stream into pools; cease to flow; and drying of the hyporheos (spaces in the stream bed that are often important refuges). Rader and Belish (1999) found that macroinvertebrate communities were resilient to mild flow alterations. However, in severely altered streams macroinvertebrate communities were significantly impaired (reduced total invertebrate density, reduced taxa richness and composition dominated by only a few taxa). Some change may have little effect but the degree or severity of change will be an important determinant of ecological outcomes. Streams that are highly dependent on groundwater discharge (based on the volume of baseflow and its temporal variability, the type of aquifer systems and rainfall) will be particularly impacted by a loss of baseflow. Groundwater dependent ecosystems are communities of plants, animals and other organisms whose distribution and life processes are dependent on groundwater (Hatton and Evans 1998). Many streams from the Great Dividing Range in South-Eastern Australia are baseflow dependent. The Horse Park Wetland in North Gungahlin, Canberra, is distinctive in that it is a groundwater-dependent one, whereas most others in the region are basin type wetlands (Barlow et al. 2005). Further investigation is required to determine the dependence of ACT stream systems on groundwater. It is worth noting that at least one of Australia’s key fauna has a strong dependency on the maintenance of river pools, if not flow, in the coastal rivers of South-Eastern Australia including Kangaroo Island: the platypus. This species is completely dependent on the continuous availability of river pools. In much of its current habitat, groundwater is likely to play a role in this. It is apparently not a requirement for platypus to have flowing waters, but if changes in groundwater availability induced a cessation of ponding in these systems at any time, then this may to lead to local extinction. It is important to note that pools have dried up on occasion on Kangaroo Island, but the platypus persisted by some as yet unknown strategy (Hatton and Evans 1998). Modelling of ACT groundwater resources done by Evans et al. (2005), suggests that the severity of changes to baseflow by groundwater abstraction would be small if abstraction is limited to the current cap of 10% of the resource in wet or dry years. However, an increase of abstraction to 20% would reduce baseflows for up to >80% of the time in dry years. Therefore, 18 Ecological effects of reducing stream baseflows based on groundwater modelling and the MLLE assessment, when conditions are extreme and drying or cease-to-flow is already stressing aquatic biota, groundwater abstraction at levels above 10% would be expected to have severe effects on aquatic biota. 6.2 Extent 2 If groundwater is abstracted on a large scale (greater than 10 km ) (particularly in the upper parts of catchments, Evans et al. 2005), the effects could include the drying out of groundwaterfed systems, including rivers and wetlands. Aquatic biota restricted to groundwater-fed areas may therefore, be particularly vulnerable to groundwater abstraction. The rate of macroinvertebrate community recovery following a disturbance is influenced by the distance of the stream to a source of potential colonists (Wallace 1990). The greater the extent of baseflow reduction and stream disturbance in a catchment, the less likely that there will be a source of colonists nearby. Rapid colonization will occur of any newly available habitat that is within the dispersal range of species living in nearby lotic or lentic habitats (Williams and Hynes 1976). Many insects are capable of flight during their adult stages and have little difficulty in recolonizing stream habitats (Williams and Hynes 1976), however, other macroinvertebrate taxa have low mobility and poor dispersal abilities. Macroinvertebrates with poor dispersal abilities may take a long time to recover if the extent of the disturbance is far reaching. The extent of reduction in baseflow will be determined by the location of groundwater abstraction as well as the volumes. Depending on the underlying geology, catchments generally dry from their upper parts first. Therefore, abstraction in upper catchments will have more effect on baseflow than in lower parts and larger volumes will also extend the effects. Both are issues that will be likely to have significant ecological effects during dry years when baseflows are maintained for extensive periods by groundwater. 6.3 Frequency and duration Low-flow events and drying are natural phenomena (McMahon and Finlayson 2003) to which aquatic ecosystem will be adapted. However, groundwater abstraction may increase the frequency of low-flow events, and some aquatic communities or species may be unable to cope with the change in flow patterns as demonstrated in the MLLE literature evaluation presented above. An increased frequency of low flow events may affect ephemeral stream systems more than perennial stream systems, because surface flow will provide more refugia for biota in the perennial stream. The ecological effect of a short-lived low-flow event is likely to be much less than one lasting for many months (Suren et al. 2003). It has been demonstrated that the ACT streams and other aquatic systems respond rapidly to rainfall and that most flows and most volume is directly rainfall related (Evans et al. 2005). Therefore, little ecological effect of groundwater abstraction at almost any level would be expected during wet periods when rainfall will contribute rapidly to surface flow. During wet years, i.e. greater than average rainfall years, there will be continuous periods of days and sometimes weeks when baseflow dominates the streamflow, and reduced baseflow may have negative ecological effects during these periods. Groundwater extraction at levels >10% of the resource is also likely to produce negative ecological effects in dryer years (i.e. a year with below annual average rainfall) by extending both the frequency and duration of drying or cessation of flow. 19 Ecological effects of reducing stream baseflows 6.4 Timing Under extremely dry conditions, small decreases in surface water flows will cause relatively large reductions in wetted channel area and thus habitat availability for aquatic organisms (McMahon and Finlayson 2003). Whereas at higher flows, quite large recessions in base-flow will have much less impact on habitat availability, because they mainly reduce water depth and these differences are mitigated by channel shape (McMahon and Finlayson 2003). Therefore, if a loss of baseflow eventuates during a dry period it will have a greater impact of the aquatic ecosystem. Groundwater modelling by Evans et al. (2005) found that for Sullivans Creek ACT, in the dry years, baseflow dominates streamflow approximately 80% of the time. For Sullivans Creek, the influence of baseflow (fraction-of-time-dominance) is stronger at the downstream gauge. For Yarralumla Creek, the reverse appears to be the case. This may be because of the baseflow 2 filter underestimating the speed of the baseflow response in the smaller (5.6km ) upstream catchment. Therefore, as noted above ecological effects groundwater abstraction may be marked during dry years but they may be modified by location in the catchment and the type of catchment. Evans et al. (2005) also found that there is a time lag involved in the impacts of pumping on stream flow that extends over many years. This results in a legacy of impact because of previous years pumping. This finding has major ecological implications. An interpretation is that the ecological impacts of groundwater pumping will be seen in dry years, even if the abstractions occurred in previous wet years. Therefore, it is not possible to manage dry and wet years independently, and so we should control abstraction for all years at a level that will be sustainable during dry years. 20 Ecological effects of reducing stream baseflows Part 3 - Are the effects of baseflow reduction stream dependent? 7 Issues – Stream characteristics The following issues may influence the effects of baseflow reduction, and are likely to be stream (or location) dependent. These include: River nutrient enrichment; Position in the stream channel network (upland vs lowland reaches); and Proximity of boreholes (distance from stream edge). 7.1 River enrichment Suren et al. (2003) suggest that the severity of low flows is influenced by a river’s degree of enrichment, with greater impacts associated with high enrichment. The enrichment status of a river may vary because of underlying geology and also because of human influences such as land-use change. Drying will generally concentrate chemical constituents such as the major ions and nutrients. Additionally, the exposure time to aquatic biota will be much greater when flows are low. Under such conditions algal growth because of enhanced nutrients combined with a lack of scouring flows can result in marked changes to primary productivity. Such conditions also result in a degradation of other aquatic biota as noted in the MLLE evaluation. 7.2 Position in the stream channel network The low flow behaviour of streams is further complicated by position in the stream channel network (McMahon and Finlayson 2003). At the upper end of channel networks (the first order streams of Strahler, 1952), channels may carry flow only immediately following rainfall. The active channel network extends upstream during wet periods in all regime and climate types. Thus, the length and severity of low flow periods, and frequency of cease-to-flow, typically decrease with distance downstream in the channel network and, therefore, increasing catchment area. Bedrock type also mitigates the nature of low-flow periods. Rivers draining catchments containing major aquifers may continue to flow during long dry periods when neighbouring streams on different bedrock have ceased to flow (McMahon and Finlayson 2003). Armitage and Petts (1992) found that upland streams did not appear to suffer adverse effects as a result of abstraction, whereas lowland streams appeared to be more degraded, but with the exception of the Pang River, this could not necessarily be attributed to abstraction. The lack of any consistent trends in taxon presence or absence may be a result of the very diverse nature of the effects of abstraction, or to the natural diversity of the rivers chosen for study. In upland streams within- and between-season flow variability is naturally high as is substratum heterogeneity. The resident fauna is therefore well adapted to extreme conditions, which may involve severe loss of wetted area (Armitage and Petts 1992). In the ACT, there are many small upland streams that have naturally low flow during summer. The aquatic fauna in these streams may be adapted to stream drying, however, if adverse conditions are prolonged the availability of temporary refugia will be limited and benthic fauna 21 Ecological effects of reducing stream baseflows losses are likely to occur. A more detailed examination is needed of the response of invertebrates to the changing hydraulic conditions following reduced or altered flows. 7.3 Proximity of boreholes Wood and Petts (1994) suggest that one of the management options for lessening the impact of groundwater abstraction on rivers is the relocation of boreholes away from sensitive stream reaches. Groundwater modelling by Evans et al. (2005) shows that the closer the bore is to the stream the faster the impact and the quicker the time to full impact but also the quicker recovery time. At a distance of 500 metres from the stream the full impact of one year of pumping is effectively detected within about 5 years, whereas, the full impact of extraction for one year at 2 km is ongoing for considerable time. This shows that the impact of pumping is not confined to the year in which it occurs. Rather, the impact is spread over many years and is proportional to the distance from the stream. As noted above the ecological implications are marked and, while ecological impacts may be seen in dry years, licensing of groundwater abstraction volumes and locations should probably be set regardless of wet or dry years. It is unknown whether the aquatic biota would be more affected by a high level of stream depletion observed over a short period of time (borehole located close to the stream), or a lower level of stream depletion observed for an ongoing period (borehole located away from the stream). However, this difference is only observed for short-term pumping (one year of pumping followed by 125 years of no pumping). The relocation of boreholes suggested by Wood and Petts (1994) is unlikely to be an effective strategy if there is continuous groundwater pumping, because stream depletion is similar for the different pumping distances (Evans et al. 2005). The impact of groundwater extraction is a prolonged process, with the time to full impact varying depending on the volume extracted and the distance of pumping from the stream (Evans et al. 2005). Thus, ecological impacts need to be considered in this context and effects somethwhat remote in time and space will need consideration. 22 Ecological effects of reducing stream baseflows Conclusions 7.4 Overall conclusions There is an impact on aquatic ecosystems by reducing baseflow in the manner caused by groundwater abstraction. In particular, reduced stream baseflows causes a decrease in macroinvertebrate taxa richness or diversity; and a decrease in macroinvertebrate abundance or density. There may be effects on other ecosystem components such as fish, macrophytes, algae and riparian vegetation, but support from the literature is weak at this stage. Abstraction of 10% of the available resource is likely to have little ecological effect because it causes only small changes in baseflow (Evans et al. 2005). Groundwater abstractions of 20% or more of the available resource are likely to have significant effects on baseflows, which in turn will produce negative ecological effects. However, the effects may be stream dependent. Investigation of stream characteristics including nutrient enrichment status, underlying geology, and natural flow variability may be needed before a general rule for groundwater abstraction can be formulated. The ecological effects of groundwater abstractions will be most profoundly noticed in dry years when stream flows are dependent on groundwater for >80% of the time. Groundwater abstractions in wet and dry years are likely to have the same effect in dry years because of the time taken for re-charge and travel to the streams. There are unlikely to be any obvious ecological effects of groundwater abstractions noticed within the wet years because most stream flow is generated by rainfall and surface runoff in the ACT region. 7.5 Information gaps There are several significant information gaps with respect to the impacts of groundwater abstraction on rivers. These issues should be addressed in the form of observational studies to gain a better understanding of the local riverine processes and the effects of abstractions. Such studies would provide valuable information for both the future management of ACT groundwater and surface water resources. Further study of the ecological effects of low flows, groundwater abstraction and recovery is required for individual rivers so that clear management plans can be made to protect both the lotic and riparian ecosystems and the groundwater resource. The main information gaps that may need addressing in conjunction with the review of groundwater requirements are listed below: Species restricted to groundwater-fed areas; the effects of atypical low flows and bed drying on the aquatic ecosystem; the nature of ecosystems' dependency on groundwater; the minimum water requirements of the ecosystem and the degree to which baseflow can be reduced without loss of habitat and refugia; the groundwater regime that will satisfy the water requirements of the ecosystem; 23 Ecological effects of reducing stream baseflows the impacts of change in groundwater regime on ecological processes and water quality; the extent of impacts of groundwater abstraction on stream systems. Future study of how water resources respond to groundwater abstractions could be implemented to help develop management approaches and achieve desired outcomes. This study could be designed in several ways to test the effects of abstraction. Suggested approaches include: 1. Implement an experimental study, which diverts water from a stream during a period when baseflow dominates; 2. Ongoing monitoring of a stream system influenced by groundwater abstractions, preferably in a system where boreholes are located in close proximity to the stream, and there are limited confounding influences; 3. Model the change in wetted channel area and habitat loss (e.g. riffles and pools) associated with groundwater abstraction; 4. Evaluate the volume of baseflow and its temporal variability, the type of aquifer systems and rainfall to determine stream dependence on groundwater. 7.6 Managing in the presence of knowledge gaps The quality and quantity of groundwater resources may be constantly changing, and there are many gaps in the knowledge of groundwater resources and the effects of groundwater use. Therefore, an adaptive management approach is recommended. 8 References ACT Government. (2004). Environmental Flow Guidelines: A Technical Background Paper. Australian Capital Territory, Canberra. Available at www.environment.act.gov.au/Files/ environmentalflowguidelines-atechnicalbackgroundpaper1204pdf.pdf. ANZECC & ARMCANZ 2000, http://www.deh.gov.au/water/quality/nwqms/pubs/wqg-ch3.pdf. Armitage, P. and Petts, G. (1992). Biotic score and prediction to assess the effects of water abstractions on river macroinvertebrates for conservation purposes. Aquatic Conservation: Marine and Freshwater Ecosystems, 2: 1-17. Evans WR, BFW Croke, JL Ticehurst, B Schoettker and AJ Jakeman (2005). Sustainable Groundwater Yield Assessment Sullivans Sub-Catchment, ACT. iCAM Client Report for Environment ACT. Integrated Catchment Assessment and Management (iCAM) Centre, School of Resources, Environment and Society, The Australian National University, Canberra, Australia. Downes, B.J., Barmuta, L.A., Fairweather, P.G., Faith, D.P., Keough, M.J., Lake, P.S., Mapstone, B.D. and Quinn, G.P. (2002). Monitoring Ecological Impacts: Concepts and Practice in Flowing Waters. (Cambridge University Press.) 446 pp. Evans W.R., B.F.W. Croke, J.L. Ticehurst and A.J. Jakeman (2004). Sustainable Groundwater Yield Assessment Woden Sub-Catchment, ACT. iCAM Client Report 2004/7 for Environment ACT. Integrated Catchment Assessment and Management (iCAM) Centre, School of Resources, Environment and Society, The Australian National University, Canberra, Australia. Environment ACT. (2004). Thinkwater, Act water Volume 3: State of the ACT’s water resources and catchments, April 2004. Australian Capital Territory, Canberra. Available at http://www.thinkwater.act.gov.au/documents/Vol3screen_000.pdf. 24 Ecological effects of reducing stream baseflows Hatton and Evans (1998). Dependence of Ecosystems on Groundwater and its Significance to Australia’ by Tom Hatton and Richard Evans, LWRRDC Occasional Paper No 12/98. Land and Water Resources Research and Development Corporation. Ivkovic, K.M., Letcher, R.A. and Croke, B.F.W. (2004). Groundwater-River Interactions In The Namoi Catchment, NSW and their Implications for Water Allocation. 9th Murray Darling Basin Groundwater Workshop "Balancing the Basin", Bendigo, 2004. Available at http://cres.anu.edu.au/people/ivkovic.pdf. Norris, R., Liston, P. Mugodo, J., Nichols, S., Quinn, G., Cottingham, P. Metzeling, L. Perriss, S., Robinson, D., Tiller, D. and Wilson, G. (2005). Multiple lines and levels of evidence for detecting ecological responses to management decisions. Proceedings of the 4th Australian Stream Management Conference: Linking rivers to landscapes. 19-22 October, 2004, Launceston: Tasmania. Rader, R.B. and Belish, T.A. (1999). Influence of Mild to Severe Flow Alterations on Invertebrates in Three Mountain Streams. Regulated Rivers: Research & Management, 15: 353-363. Wallace, J.B. (1990). Recovery of lotic macroinvertebrate communities from disturbance. Environmental Management, 14 (5): 605-620. Williams, D.D. and Hynes, H.B.N. (1976). Stream habitat selection by aerially colonizing invertebrates. Canadian Journal of Zoology 54: 685-693. Wood, P.J. and Petts, G.E. (1994). Low Flows and Recovery of Macroinvertebrates in a Small Regulated Chalk Stream. Regulated Rivers: Research & Management, 9, 303-316. 9 Acknowledgements This project built on prior work of the Cooperative Research Centre for Freshwater Ecology (CRCFE). Several staff members were involved in the initial development of the MLLE procedure and software. Thank you to Barry Croke, Ray Evans, and Birte Schoettker (Salientsolutions/ICAM Team). 10 Glossary Abstraction Abstraction refers to the removal of water from a natural waterway, impoundment or bore. Allochthonous material Exogenous food organisms, organic matter, and nutrients originating outside and transported into an aquatic system (Armantrout, 1998). Autochthonous Endogenous materials such as nutrients organisms fixed or generated within the aquatic system (Armantrout, 1998). Aquifer An aquifer is a layer of rock or soil that is permeable and has the capacity to convey significant amounts of groundwater. Baseflow Baseflow describes the quantity of flow in a waterway that exists purely as a result of seepage into the upstream channel from groundwater. Practically, baseflow is determined from either field investigation after a prolonged period without precipitation or one of several quantitative baseflow separation models. Ephemeral Streams Ephemeral streams are waterways that are temporary in nature. That is, waterways that exist for a relatively short period of time, usually a matter of days, after a storm event. 25 Ecological effects of reducing stream baseflows Flow Regime Flow regime commonly describes the distribution of flow rate magnitudes over time for a particular waterway. In this capacity it is similar to a unit hydrograph. Fractured Rock Aquifer A fractured rock aquifer is an aquifer that exists where the geological structure is characteristically impervious rock with sediment filled fractures. These fractures allow the conveyance of groundwater. Hyporheos Latticework of underground habitats through the alluvium of the channel and floodplain associated with streamflows that extend as deep as the interstitial water in the substrate. Lotic Aquatic system with rapidly flowing water, such as a creek, stream or river, where the net flow of water is uni-directional from the headwaters to the mouth. Lentic An aquatic system with standing or slow flowing water (e.g. lake, pond, reservoir, swamp, marsh and wetland). Such systems have a non-directional net flow of water. Macroinvertebrate Aquatic animals without backbones that can be seen with the naked eye, e.g., shrimps, worms, crayfish, aquatic snails, mussels, aquatic stage of some insect larvae, such as dragonfly larvae, mayflies, caddisflies, etc. Macrophytes Macrophytes are large water plants. Emergent macrophytes are plants that are rooted in the riverbeds or lakebeds, and protrude from the water surface. Submerged macrophytes are plants that are rooted in the riverbeds or lakebeds, but do not protrude from the water surface. Refugia Areas that have escaped ecological changes or stress occurring elsewhere and so provide a suitable habitat for organisms to survive (Boulton and Brock, 1999). Riparian Vegetation Riparian vegetation is terrestrial vegetation that is influenced by its proximity to a body of water. Storativity The volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head. It is equal to the product of specific storage and aquifer thickness. In an unconfined aquifer, the storativity is equivalent to the specific yield. Also called storage coefficient. Transmissivity Rate at which water is transmitted through a unit width of an aquifer under a unit hydraulic gradient. Transmissivity values can be expressed as square metres per day (m2/d) or square metres per second (m2/s). 26 Ecological effects of reducing stream baseflows Appendix A – MLLE References The following references were used in the MLLE assessment: Armitage, P.D. and Petts, G.E. (1992). Biotic score and prediction to assess the effects of water abstractions on river macroinvertebrates for conservation purposes. Aquatic Conservation: Marine and Freshwater Ecosystems, 2: 1-17. Armitage, P.D., Gunn, R., Furse, M., Wright, J. and Moss, D. (1987). The use of prediction to assess macroinvertebrate response to river regulation. Hydrobiologia,144: 25-32. Barlow, A., Lawrence, I., Williams, D., Osborne, W. and Norris, R. (2005). Horse Park Wetland Environmental Assessment Report, August 2005. Water Research Centre, University of Canberra, Australia. Bickerton, M., Petts, G., Armitage, P., Castella, E. (1993). Assessing the ecological effects of groundwater abstraction on chalk streams: Three examples from Eastern England. Regulated Rivers: Research and Management, 8: 121-134. Boulton, A.J. (2003). Parallels and contrasts in the effects of drought on stream macroinvertebrate assemblages. Freshwater Biology, 48: 1173-1185 Bromley, J., Cruces, J., Acreman, M., Martinez, L., Llamas, M.R. (2001). Problems of Sustainable Groundwater Management in an Area of Over-exploitation: The Upper Guadiana. Water Resources Development, 17(3): 379-396. Caruso, B.S. (2002). Temporal and spatial patterns of extreme low flows and effects on stream ecosystems in Otago, New Zealand. Journal of Hydrology, 257: 115-133. Castella, E., Bickerton, M., Armitage, P.D. and Petts, G.E. (1995). The effects of water abstractions on invertebrate communities in U.K. streams. Hydrobiologia, 308:167-182. Chester, H. and Norris, R. (2005). Dams and Flow in the Cotter River: Effects on instream trophic structure and benthic metabolism. CRC Freshwater Ecology, University of Canberra, Australia. Choi, S.U., Yoon, B. and Woo, H. (2005). Effects of Dam-induced Flow Regime Change on Downstream River Morphology and Vegetation Cover in the Hwang River, Korea. River Research and Applications, 21: 315-325. 27 Ecological effects of reducing stream baseflows Cortes, R., Ferreira, M., Oliveira, S., and Oliveira, D. (2002). Macroinvertebrate community structure in a regulated river segment with different flow conditions. River Research and Applications, 18: 367-382. Englund, G., Malmqvist, B., and Zhang, Y. (1997). Using predictive models to estimate effects of flow regulation on net-spinning caddis larvae in North Swedish rivers. Freshwater Biology, 37: 687-697. Englund, G., and Malmqvist, B. (1996). Effects of flow regulation, habitat area and isolation on the macroinvertebrate fauna of rapids in North Swedish rivers. Regulated Rivers: Research and Management, 12: 433-445. Holmes, N.T.H. (1999). Recovery of headwater stream flora following the 1989-1992 groundwater drought. Hydrological Processes, 13 (3): 341-354. Johnson, I., Elliott, C., and Gustard, A. (1995). Modelling the Effect of Groundwater Abstraction on Salmonid Habitat Availability in the River Allen, Dorset, England. Regulated Rivers: Research and Management, 10: 229-238. McIntosh, M., Benbow, M., and Burky, A. (2002). Effects of Stream Diversion on Riffle Macroinvertebrate Communities in a Maui, Hawaii, Stream. River Research and Applications, 18: 569-581. Norris, R., Chester, H. & Thoms, M. (2004). Ecological sustainability of modified environmental flows in the Cotter River during drought conditions January 2003-April 2004: Final report. CRC Freshwater Ecology, University of Canberra, Australia. Peat, M. and Norris, R. (2005). The effect of low flow variation on periphyton downstream of dams in the Cotter River. CRC Freshwater Ecology, University of Canberra, Australia. Peat, M. and Norris, R. (2005). The biological condition of Cotter River during a drought flow regime: December 2004. CRC Freshwater Ecology, University of Canberra, Australia. Rader, R.B. and Belish, T.A. (1999). Influence of mild to severe flow alterations on invertebrates in three mountain streams. Regulated Rivers: Research and Management, 15: 353-363. Roberts, K. (2000). The effects of drought on community macroinvertebrates: Honours thesis. University of Canberra. structure of stream 28 Ecological effects of reducing stream baseflows Strevens, A.P. (1999). Impacts of groundwater abstraction on the trout fishery of the River Piddle, Dorset; and an approach to their alleviation. Hydrological Processes,13: 487-496. Suren, A., Biggs, B., Duncan, M., Bergey, L., and Lambert, P. (2003). Benthic community dynamics during summer low-flows in two rivers of contrasting enrichment 2. Invertebrates. NZ Journal of Marine and Freshwater Research, 37: 71-83. Wood, P.J., and Petts, G.E. (1994). Low flows and recovery of macroinvertebrates in a small regulated chalk stream. Regulated Rivers: Research and Management, 9: 303-316. Wood, P.J. and Petts, G.E. (1999). The influence macroinvertebrates. Hydrological Processes, 13: 387-399. of drought on chalk stream Zektser, S., Loaiciga, H.A., Wolf, J.T. (2005). Environmental impacts of groundwater overdraft: Selected case studies in the southwestern United States. Environmental Geology, 47: 396-404. 29