The U.S. EPA’s Stressor Identification (SI) Guidance (U.S. EPA 2000) was used to identify and rank the probable physical, chemical, and biological stressors that have impaired the aquatic community in Clear Fork of Coal River, West Virginia. A conceptual model illustrated linkages between candidate causes and their biological effects based on general ecological knowledge. Stressor-response threshold values were based on statistical analyses of statewide data. Relative positions of sampling locations were mapped (from downstream to upstream), along each impaired stream and its tributaries, within a subwatershed.
Two types of evidence were used to screen out candidate causes that did not co-occur with effects and those that had no source to enable occurrence using watershed characteristics such as land use and soils, point-source inventories, site observations, and other evidence. Remaining candidate causes were ranked according to the weight of evidence (strongest to weakest) within each watershed. Types of evidence included stressor-response threshold values from the statewide data analyses, and predictive models of specific biological changes associated with candidate causes. Field notes were also consulted for other evidence or explanations for any inconsistencies. These analyses and thresholds were used to assess whether the stressor occurred at a sufficient intensity to cause biological impairments in specific portions of the watershed. We plotted and analyzed quantitative data spatially using a “geo-order” format.
Probable causes were different throughout the watershed and the combination of all these causes was evident in the mainstem, which exhibited some resiliency due to dilution and different geophysical attributes. In particular, causes included metal contamination and acidification from mine draining, aluminum toxicity in association with low pH, elevated conductivity, sediment deposition, organic enrichment from direct releases and from algal productivity enhanced by nutrients, and low dissolved oxygen.