Invertebrate communities of small streams in northeastern Wyoming

Invertebrate communities of small streams in an energy-mineral- development area in the Powder River structural basin of northeastern Wyoming were studied during 1980-81. The largest average density of benthic invertebrates among 11 sites was 983 invertebrates/sq ft at a site on a perennial stream, the Little Powder River at State Highway 59. The smallest average densities were 3.4 invertebrates/sq ft in Salt Creek and 16.6 invertebrates/sq ft in the Cheyenne River, two streams where the invertebrates were stressed by degraded water quality or inadequate substrate or both. The rates of invertebrate drift were fastest in three perennial streams, compared to the rates in intermittent and ephemeral streams. Analysis of the invertebrate communities using the Jaccard coefficient of community similarity and a cluster diagram showed communities inhabiting perennial streams were similar to each other, because of the taxa adapted to flowing water in riffles and runs. Communities from sites on ephemeral streams were similar to each other, because of the taxa adapted to standing water and vegetation in pools. Communities of intermittent streams did not form a group; either they were relatively similar to those of perennial or ephemeral streams or they were relatively dissimilar to other communities. The communities of the two streams stressed by degraded water quality or inadequate substrate or both, Salt Creek and the Cheyenne River, were relatively dissimilar to communities of the other streams in the study. (USGS)