Buffalo River Watershed Biotic Stressor Identification

A Stressor Identification (SID) analysis is a step-by-step approach for identifying the probable cause(s) of biological impairment in a stream system. There are four stream reaches within the Buffalo River Watershed that were identified as impaired for aquatic life based upon poor Index of Biological Integrity (IBI) scores that indicate an unhealthy biological community. Further evaluation was completed to connect the biological community to the stressor(s) causing the impairment. This report describes the evaluation of the environmental data and the diagnoses of the probable causes for the biological impairments. Numerous candidate causes for impairment were evaluated using the U.S. Environmental Protection Agency's (EPA's) Causal Analysis/Diagnosis Decision Information System (CADDIS), the Minnesota Pollution Control Agency's (MPCA's) biological Total Maximum Daily Load (TMDL) protocols, and a weight of evidence analysis. The Buffalo River Watershed is a complex system with great diversity in topography, stream channel type and condition, soils, and drainage intensity. This diversity results in a variety of conditions that support a broad spectrum of fish and aquatic macroinvertebrate life. The SID analysis determined the probable stressors in each of the four impaired reaches. The stressors found to be acting upon the Buffalo River system include high sediment/turbidity, lack of connectivity, lack of habitat availability, altered hydrology, and low dissolved oxygen (DO). In addition to these stressors, high phosphorus, high nitrate, and pesticides were reviewed for their potential influence on the biology of the impaired reaches.