Effects of Siltation and Coarser Sediments on Distribution and Abundance of Stream-Inhabiting Insects

This study was conducted to show the effects of sand and coarser sediments on the distribution and abundance of insects in Emerald Creek and the Middle Fork of the St. Maries River. Stream profile, substrate conditions, water chemistry and benthos were measured at seventeen permanent stations. Substrate simulation studies were conducted in an artificial stream in the laboratory to better define the relationship of substrate to five species of aquatic insects. Coarse and fine gravels with unimbedded cobble were preferred over fine sands and silt with partially or completely imbedded cobble by most insects. Habitats with few cobble and large amounts of sand and silt had low species diversities and biomass. Abnormal sediment production from rockhounding, dredge mining and roadbuilding cause adverse effects on the stream environment and insects