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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Disturbance Ecology III
AQUATIC INSECT ASSEMBLAGE RESPONSE TO STREAMFLOW ABSTRACTION.
D.M. Pepin and N.L. Poff. Department of Biology, Colorado State University, Fort Collins, CO 80523-1878
Streamflow abstractions are pervasive alterations to natural flow regimes throughout arid lands worldwide. Despite their widespread occurrence and the growing recognition that flow alteration impairs water quality and ecosystem health, there is little empirical evidence linking streamflow diversion to ecosystem structure or function. We sampled benthic macroinvertebrates and measured physical habitat conditions above and below diversion structures on 6 streams with long-established diversions to test the hypothesis that, compared to undiverted reaches, assemblages collected from diverted reaches would show reduced richness and be dominated by tolerant taxa. Study reaches occur at approximately 2900 m asl on streams draining the western slope of the continental divide in Colorado. Their waters are diverted year-round, resulting in flow reductions of 30% to nearly 100%. Diverted reaches showed coarsened substrata, with d16 increasing 2 to 10 times and d84 1.25 to 2 times in the least and most diverted reaches, respectively. Similarly, the most severely diverted reaches exhibited a greater range in daily temperatures than less diverted streams. Total macroinvertebrate density and richness were significantly lower in samples collected from diverted reaches. EPT assemblages were evenly structured above diversions, but dominated by tolerant Heptageniidae in diverted reaches.
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