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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Disturbance Ecology II
BENTHIC RESPONSE TO A MULTI-YEAR EXPERIMENTAL FLOOD REGIME BELOW A LARGE DAM.
C.T. Robinson, U. Uehlinger, S. Aebischer, C. Jakob, and M.T. Monaghan. Department of Limnology, EAWAG/ETH, Ueberlandstrasse 133, 8600 Duebendorf, Switzerland
Globally, over 40,000 large dams (>15 m high) are presently in operation. One scenario to improve the ecological integrity of downstream reaches is using artificial floods to simulate the 'natural' flow regime. We present the results from a flood implementation program encompassing multiple within-year floods over two consecutive years. Periphyton and zoobenthos were monitored one year prior and then periodically before and after each flood, and compared to an adjacent reference system. We also examined the lateral dispersal and deposition of invertebrates during two floods in the second year, and assessed different instream habitats as refugia. Flooding reduced benthic abundances in each year but recovery trajectories differed considerably due to differences in assemblage composition between years (a historical influence of previous floods was evident). Periphyton assemblages shifted from a moss predominance to one of thick (>4 cm) diatomaceous mats (primarily Didymosphenia sp.), and zoobenthos was dominated by disturbance resistant taxa in year 2. Drift during each flood was catastrophic in pattern and laterally constrained by valley confinement. Flood effects varied by habitat type with bedrock habitats showing the lowest reduction in animal abundance.
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