A fine line

Posted on September 26, 2009

Human disturbance tends to increase the amount of fine sediment entering freshwater streams.  High loads of fine sediment in streams can have negative effects on the growth, reproduction and migration of fish, but there have been few attempts to define threshold sediment concentrations above which fish communities are significantly impacted.  Data gathered from mountain streams in 12 western U.S. states showed that an ecological condition score based on the diversity and biology of fish and amphibians fell by 4.7% for each 10% increase in fines (defined as bottom sediment particles less than 0.06 mm in diameter).  To conserve aquatic vertebrates in these mountain streams, fines should not exceed 5% of all sediment particles. 

Reference:   Bryce, S.A., Lomnicky, G.A., Kaufmann, P., McAllister, L.S. & Ernst, T.L.  2008.  Development of biologically based sediment criteria in mountain streams of the western United States.  North American Journal of Fisheries Management 28, 1714–1724.