Fish Assemblage Responses to Water Withdrawals and Water Supply Reservoirs in Piedmont Streams |
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Authors: | Mary C Freeman Paula A Marcinek |
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Institution: | (1) US Geological Survey, Patuxent Wildlife Research Center, University of Georgia, Athens, Georgia 30602, USA;(2) Institute of Ecology, University of Georgia, Athens, Georgia 30602, USA |
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Abstract: | Understanding effects of flow alteration on stream biota is essential to developing ecologically sustainable water supply
strategies. We evaluated effects of altering flows via surface water withdrawals and instream reservoirs on stream fish assemblages,
and compared effects with other hypothesized drivers of species richness and assemblage composition. We sampled fishes during
three years in 28 streams used for municipal water supply in the Piedmont region of Georgia, U.S.A. Study sites had permitted
average withdrawal rates that ranged from < 0.05 to > 13 times the stream’s seven-day, ten-year recurrence low flow (7Q10),
and were located directly downstream either from a water supply reservoir or from a withdrawal taken from an unimpounded stream.
Ordination analysis of catch data showed a shift in assemblage composition at reservoir sites corresponding to dominance by
habitat generalist species. Richness of fluvial specialists averaged about 3 fewer species downstream from reservoirs, and
also declined as permitted withdrawal rate increased above about 0.5 to one 7Q10-equivalent of water. Reservoir presence and
withdrawal rate, along with drainage area, accounted for 70% of the among-site variance in fluvial specialist richness and
were better predictor variables than percent of the catchment in urban land use or average streambed sediment size. Increasing
withdrawal rate also increased the odds that a site’s Index of Biotic Integrity score fell below a regulatory threshold indicating
biological impairment. Estimates of reservoir and withdrawal effects on stream biota could be used in predictive landscape
models to support adaptive water supply planning intended to meet societal needs while conserving biological resources. |
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Keywords: | Stream fish Species richness Flow depletion Hydrologic alteration Water supply planning |
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