Benthic Macroinvertebrate Assemblages in Kryal and Rhithral Lake Outlet Streams in the North Cascade Mountains

Abstract

Abstract Alpine aquatic environments are one of the harshest on earth and are sensitive indicators of climate change. In Washington, the most glaciated state in the contiguous United States, relatively little is known about the effect of loss of glacial water sources on macroinvertebrate communities. Our study compares the water quality conditions and composition of benthic macroinvertebrates from five rhithral (snowmelt-fed) and five kryal (glacially-fed) lake outlet streams in the North Cascade Mountains, WA. Kryal streams were characterized by lower water temperatures, higher discharge rates, higher turbidities, and less stable in-stream channels compared to rhithral sites. A total of 24 985 specimens representing 96 macroinvertebrate taxa were collected. Rhithral lake outlet streams had significantly higher densities and supported more taxa than kryal sites (9049 individuals m-2 and 82 taxa versus 821 individuals m-2 and 38 taxa). Chironomidae dominated macroinvertebrate populations at all sites, alth...