Modification of an ecotoxicological rating to bioassess small acid mine drainage-impacted watersheds exclusive of benthic macroinvertebrate analysis.

The modified ecotoxicological rating (METR) approach to synthesizing integrative bioassessment data into a single number ranging from 0 to 100 was found to differentiate between multiple levels of impacts from acid mine drainage (AMD). Our objective was to develop a more cost-effective and time-efficient bioassessment technique than previously used in other large scale ecotoxicological ratings (ETRs) by minimizing the number of parameters required to rank stations to only those most descriptive of the benthic macroinvertebrate community responses to AMD. Nineteen physical, chemical, toxicological, and ecological measurements were made at 38 stations in two adjacent watersheds. The most descriptive parameters were selected through multiple linear regression analysis, bivariate correlation analysis, and one-way analysis of variance. We found that habitat assessment, 30-d in situ Asian clam survival, mean conductivity, and mean total water column concentration of aluminum and manganese were the most descriptive parameters. The METR constructed from these parameters was equally effective at differentiating stations as were two previous published ETRs that incorporated up to 10 parameters, including benthic macroinvertebrate indices. When the METR was applied to a new watershed, the scores were significantly correlated with benthic macroinvertebrate indices for those stations.