WWRC 90-32
Ecological Consequences of Sediment Input to a Mountain Stream Insect Community: A Self-Mitigating System
Abstract
The Cheyenne Stage II Diversion Project began in 1983 in an effort
to collect 23,000 acre-feet of water annually from 30 tributary
streams of the North Fork of the Little Snake River (NFLSR). As
a consequence of the Diversion Project, Green Timber Creek (a
steep, rough, regulated tributary of the NFLSR) received 1,500 m3
of a broad-sized range of sediment in May, 1988. Both Green Timber
Creek and the NFLSR support the largest known, essentially pure
population of the endangered Colorado River cutthroat trout,
Oncorhvnchus clarki pleuriticus Cope. Because the primary food
source for the cutthroat trout is aquatic insects, a study was
conducted to assess the impact of sediment deposition on the
aquatic insect community. Our 1989 study found that the addition
of the sediment had a minimal impact on the abundance and diversity
of aquatic insects. These results were similar to a more extended
study conducted on the impact of sediment deposition in the NFLSR.
The apparent lack of significant impact may be a result of: (1)
rapid recolonization, (2) exposure of the embedded substrate by
high, spring flow rates, (3) continuous transportation of finer
sediments from the drainage, and (4) effective utilization of
large, sediment particles by the aquatic community.
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