Influence of Stream Habitat and Land Use on Macroinvertebrate Assemblages of The Henry's Fork Watershed

Abstract

We investigated relationships among benthic macroinvertebrate assemblages, stream physical habitat, and land use in the Henry's Fork watershed, Idaho and Wyoming. Macroinvertebrate assemblages were described with five biological metrics: benthic macroinvertebrate density, taxa richness, EPT (Ephemeroptera, Plecoptera, Trichoptera) richness, percent EPT, and percent dominant taxon. Ten physical habitat variables were used to describe the inorganic and organic substrate and channel morphology of the streams sampled. Land use in 10 subwatersheds was assessed using a Geographic Information System (GIS). Pearson product-moment and canonical correlation analyses were used to assess relationships among the macroinvertebrate, habitat, and land-use variables. Macroinvertebrate density, EPT richness, and dominant taxon metrics were highest in spring-fed streams with small, yet likely stable, highly embedded substrates and abundant macrophyte growth. The percent EPT metric was highest in runoff-dominated streams with large, heterogeneous, less embedded substrates. Taxa richness was negatively correlated with percent rangeland, and percent EPT was negatively correlated with percent agricultural land. The EPT richness metric was positively correlated with percent forested land. There were no significant correlations between stream habitat and land use, indicating that land use may have influenced macroinvertebrate assemblages via water quality or physical habitat characteristics not measured in this study.