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HISTORICAL CHANGES RELATED TO FLOW REGULATION OF THE RIVER
<br />HURRAY, SOUTH AUSTRALIA. I. THE BIOLOGICAL ENVIRONMENT. M.C.
<br />Thoms and K.F. Walker, River Murray Laboratory, Department of
<br />Zoology, University of Adelaide, South Australia 5000.
<br />Most biological indicators indicate that the lower Murray ecosystem is
<br />undergoing a protracted re-adjustment to the imposition of flow
<br />regulation in the 1920s. Populations of native species, including
<br />waterfowl, fish and invertebrates have declined, and there have been
<br />changes also in the composition and distribution of riverine and
<br />floodplain communities. The changed environment is more favourable
<br />for a variety of introduced species, notably fish and willows and other
<br />riparian plants. The changes aze evident on abroad-scale, related to the
<br />effects of dams in areas further upstream. They aze evident also in
<br />relation to a series of 10 low-level weirs distributed along the lower river
<br />and, at a still finer level of resoultuion, between individual weirs.
<br />Although efforts are being made to promote the conservation of native
<br />communities, the preservation of the natural environment is seen by
<br />management as merely one option among several. The regulated river is
<br />unstable, physically and biologically, and is likely to undergo more
<br />changes in future.
<br />PHYSICAL HABITAT CHANGES AND MACRO-INVERTEBRATE RESPONSE TO RIVER REGULATION
<br />CASE STUDY OF THE RIVER REDE, UK. Geoff Pettsl, Patrick Armitage2 and
<br />Emmanuel Castellal. 1Freshwater Environments Group, International Centre of
<br />Landscape Ecology, Department of Geography, Loughborough University of
<br />Technology, Leicestershire, LE11 3TU, UK. ZInst. Freshwater Ecology, River
<br />Laboratory, East Stoke, Wareham, Dorset, BH2O 6BB, UK.
<br />The River Rede is a north bank tributary of the River Tyne. Runoff from the 40 km~
<br />headwater catchment has been regulated by Catcleugh Reservoir since 1905. The
<br />impounding reservoir significantly regulates flows, effectively traps the sediment load,
<br />and maintains low flows at 50X above normal levels.
<br />The geomorphology of the river defines two distinct functional sectors within a 17 km
<br />reach below the dam. Within the first, the channel morphology has adjusted to the
<br />regulated flow regime and channel dimensions have been significantly reduced. The
<br />second, downstream sector, is straighter and relatively stable; flows are to some degree
<br />accommodated within the existing channel form but are also naturalized by tributary
<br />runoff.
<br />Macro-invertebrate samples were obtained for riffle sites: 2 upstream of the reservoir,
<br />4 within the adjusted sector, and 6 in the downstream sector. At each site two samples
<br />were obtained: three-minute kick-samples from each of the main flow end marginal areas.
<br />At each site discharge was determined by flow gauging and conductivity measured. For
<br />each sample, hydraulic conditions were described by 10 measurements of velocity, depth
<br />and shear stress (using Statzner Hemispheres), and fifty measurements (intermediate
<br />axis) of surface sediments were made. The analyses were organized to investigate three
<br />questions: 1) how does the invertebrate community vary downstream between reaches?, 2)
<br />are marginal and main flow communities different?, and 3) to what extent is the riffle
<br />fauna consistent ruithin reaches?
<br />A clear pattern is described by the faunal data for sites downstream of the dam, and
<br />this pattern is highly correlated with the environmental data. At the species level
<br />there is a clear difference between the upstream reach and the adjusted sector, then the
<br />fauna recover downstream. The adjusted sector is characterized by Leutra genicuLata,
<br />Polycentropus flavomaculatus and Hydropsyche spp. whilst several species are absent or
<br />markedly diminished in abundance. The Ephemeroptera are shown to be the best describers
<br />of spatial structure, confirming the results of other surveys of upland rivers in the
<br />UK.
<br />Although data for channel margins end main flow showed a consistent pattern, the faunal
<br />variability between sites within reaches is shown to be higher than the variability
<br />between reaches. The adjusted reach has a length of only 1000 m and although the riffle
<br />habitats show relatively subtle differences, two distinct types of riffle are defined by
<br />the faunal data.
<br />The results indicate that in the analysis of effects of regulation on macroinvertebrate
<br />faunas, the definition of functional sectors as the basis of invertebrate sampling
<br />strategies must be supplemented by a site-based typology based on hydraulic parameters.
<br />For management purposes, effort should be directed to increasing the number of sites
<br />examined, but a trade-off may be made by sampling only the main flow areas and focusing
<br />on Ephemeroptera.
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