Knife River Macroinvertebrate and Sediment Survey

Abstract

This effort was conducted as part of the Knife River TMDL (total maximum daily load) study for turbidity, and includes data to compare invertebrate community composition, habitat structure, and sediment deposition among Knife River sites. Macroinvertebrate, stream substrate, water quality, and fish and invertebrate habitat data were collected from five sites along the Knife River and its tributaries in August 2006. The study’s objectives were two-fold: first, to collect baseline data from several locations within the Knife River watershed, which is currently listed as impaired for turbidity; and second, to compare these data to historical data from the Knife River watershed and other North Shore streams. Turbidity and embeddedness affect stream invertebrates and fish by raising water temperature, reducing search distances for visual predators, clogging or abrading delicate gill tissue, filling in interstitial spaces among stream cobbles, and other detrimental effects. To put current data into perspective, Knife River TMDL sample locations were compared to historical samples within the Knife River watershed and other North Shore streams using macroinvertebrate assemblage metrics and, for one set of samples, substrate and water physical parameters. Due to differences in sampling methodology, macroinvertebrate metrics had to be calculated differently for comparison with historical data.