Diagnostic Applications of a Fish Community-Based Stressor Index

Biological communities reflect environmental conditions, and not only indicate whether water quality standards are being met and designated uses supported, but can also serve as diagnostic indicators for stressors that are otherwise difficult and/or expensive to monitor.  This diagnostic ability, in part, derives from differential tolerance of species; the presence/absence and abundance of individual species (and how these species comprise a community) can be used to infer relevant stressors.  Using concurrently-collected fish community and water quality data from Minnesota streams and rivers, species-level Tolerance Indicator Values (TIVs) were developed for individual water quality parameters. Species-level TIVs were aggregated to derive community-level Stressor Index Values (SIVs). SIVs were used to predict the probability of meeting Minnesota water quality standards for specific parameters. This approach has demonstrated utility for a) identifying locations of potential (but unmonitored) water quality impairments, b) causal diagnosis of biological impairments, and c) monitoring changes in water quality over time and space. Diagnostic TIV/SIV models have currently been developed for dissolved oxygen and total suspended solids and are being used to evaluate these parameters as potential causes of aquatic life impairments in Minnesota.