Search

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.

Summary Fires and river regulation are disturbances affecting many aquatic ecosystems worldwide. We examined the ecological response of rivers to the combined effects of regulation and fire. Changes in communities of benthic aquatic algae and macroinvertebrates were studied for 22 months following a wildfire through forested catchments in the Australian Capital Territory. In both the regulated (by dams) and the free-flowing rivers and streams, fire caused large changes to physical habitat for the benthic communities that overrode the effects of regulation. In unregulated streams, the benthic communities had largely recovered 22 months after the fire disturbance, but the regulated stream did not recover. It is not clear from the findings of this study if the benthic communities will recover from the fire disturbance without active restoration of stream habitat.