Dams and Flow in the Cotter River, Australia: Effects on Instream Trophic Structure and Benthic Metabolism |
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Authors: | Heath Chester Richard Norris |
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Institution: | (1) Cooperative Research Centre for Freshwater Ecology, University of Canberra, Canberra, ACT, 2601, Australia |
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Abstract: | This study assessed benthic macroinvertebrates and periphyton and its responses to managed river-flows, in riffles downstream
of three dams on the Cotter River, Australian Capital Territory. Benthic macroinvertebrates and periphyton were also assessed
in adjacent tributaries of the river, as well as in a nearby unregulated river and its tributaries. Food sources of four macroinvertebrate
taxa (Leptophlebiidae, Elmidae, Glossosomatidae and Orthocladiinae) were determined by stable isotope analysis of the invertebrates
and their potential food, in conjunction with examination of the gut contents of individual invertebrates. Components of benthic
periphyton were the main food source for the selected taxa. Orthocladiinae consumed primarily amorphous detritus, while Elmidae,
Glossosomatidae and Leptophlebiidae consumed diatoms. Enclosed benthic chambers were used to measure the response of benthic
metabolism to monthly flow spikes released from one of the dams. The balance of benthic metabolism as measured by the Production/Respiration
ratio (P/R) showed a shift towards production after the release of flow spikes. At sites downstream of the dams, there was
more periphyton chlorophyll-a in the form of filamentous green algae than at sites in the unregulated river and the tributaries,
and macroinvertebrate taxa using periphyton as a food resource were missing or reduced in abundance relative to sites without
dams. However, the site downstream of the dam with environmental flow releases had more macroinvertebrate taxa and less periphyton
cholorophyll-a content than sites downstream of dams without managed environmental flows, suggesting that a more suitable
food supply resulting from environmental flow releases shifted macroinvertebrate communities towards those of unregulated
streams. |
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Keywords: | metabolism periphyton macroinvertebrates diet environmental flows stable isotopes |
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