Invertebrate communities of small streams in northeastern Wyoming

Abstract

Invertebrate communities of small streams in an energy-mineraldevelopment area, the Powder River structural basin of northeastern Wyoming, were studied during 1980-81. The largest average density of benthic invertebrates among 11 sites was 1,040 invertebrates per square foot at a site on a perennial stream, the Little Powder River at State Highway 59. The smallest average densities were 3.4 invertebrates per square foot in Salt Creek and 16.6 invertebrates per square foot in the Cheyenne River, two streams where the invertebrates were stressed by degraded water quality or inadequate substrate or both. The drift rates of invertebrates were larger in three perennial streams than the drift 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. INTRODUCTION The large and continuing expansion of the energy-mineral industry in the Powder River structural basin has created public interest in the condition of streams of the area. The energy-mineral developments of greatest economic importance currently (1985) are coal surface mines and oil wells, but uranium and bentonite also have been mined in the basin. Most streams in the area of active development are small plains streams that do not support a sport fishery, provide a municipal water supply, or provide substantial quantities of water for irrigation; consequently they have received little attention. The resulting lack of data has handicapped regulatory agencies, land-use planners, industry, and other groups concerned with assessing the possible effects of energy-mineral development on the flow and aquatic environment of small streams. Because invertebrate communities are indicators of the quality of the aquatic environment, the U.S. Geological Survey conducted a study of invertebrate communities in the Powder River structural basin during 1980-81 as part of its Coal Hydrology Program. Knowledge of the composition of benthijc invertebrate communities can be useful in water-quality studies, as well as in evaluating ecological effects of energy-mineral development. Past environmental conditions in a stream can be theorized by studying the existing aquatic community, because the community is composed of types of organisms adapted to the long term environmental conditions. The use of aquatic invertebrates as indicators of water quality has been well documented (Larimore, 19(74; Wilihm and Dorris, 1966). Purpose and Scope The purpose of this report is communities of streams in an energyuseful to regulatory agencies, industry an attempt was made to determine which unique to alluvial valley floors, community that could be used in identification occurrence of invertebrate communiti and their potential for recolonization to describe the benthic invertebrate nineral-development area, in a manner and other groups. During this study, if any, aquatic invertebrates are and whether they form a recognizable of alluvial valley floors. The s restricted to a flowing-water habitat Eleven stream sites were sampl 4 other sites were sampled on a sampled in stream riffles, runs, and determine the community composition, made to characterize the habitat community development. ed 7 t:L