Knife River stressor identification, Kanabec County, Minnesota.

The Environmental Protection Agency (EPA) developed the Stressor Identification (SI) process to identify stressors causing biological impairment. The SI process precedes a TMDL (Total Maximum Daily Load) and offers a means by which developers of a TMDL can more confidently identify stressor(s) causing impairment. The EPA's Causal Analysis/Diagnosis Decision Information System (CADDIS) framework was utilized to develop a SI for the Knife River Basin, Kanabec County, Minnesota. Data collected by the Minnesota Pollution Control Agency (PCA) during biomonitoring and the EPA's STORET database were analyzed using nonmetric multidimentional scaling (NMDS) ordination to evaluate the relationships between fish species and abundance, and environmental and chemical stressors. A least-squared regression between fish index of biotic integrity (IBI) scores and environmental variables was also calculated. The NMDS analysis suggests there is similarity between the two headwater sites, which are correlated with low gradient and a high percent fines, agriculture, urban, and rangeland. High gradient, percent forest and percent riffles were correlated with the mid-stream reaches of the Knife River. Only pH was significantly correlated with fish IBI scores (p=0.034). The Knife River SI identified three potential stressors; low dissolved oxygen (DO), high pH, and excess bedded sediment.