Recovery of Macroinvertebrate Communities from Metal Pollution in the South Fork and Mainstem of the Coeur d'Alene River, Idaho: 1968-1991

Mining has severely impacted the biota in the Coeur d'Alene River drainage of northern Idaho. The benthic community of the South Fork and mainstem was monitored from 1968-1971 and 1987-1991 to ascertain the effects of improved mine wastewater treatment and mine closures. Zinc concentrations decreased from 21 mg/l to 3 mg/l over this period. Subsequently, the benthic community showed a dramatic recovery as evidenced by large increases in species richness (0-18), Ephemeroptera-Plecoptera-Trichoptera index (0-8), and species diversity (0-1.8). Although considerable recovery has occurred, biotic parameters at impacted sites continue to lag behind those at reference sites, probably due to continued high zinc concentrations and poor habitat structure. A rapid bioassessment study was conducted on the South Fork of the Coeur d'Alene River and selected tributaries in northern Idaho. Species richness, Ephemeroptera-PlecopteraTrichoptera (EPT) index, and species diversity showed strong negative correlations with habitat assessment scores (mean r 2 =.68). Regression coefficients for percent dominant taxon, modified Hilsenhoff's index, and EPT/Chironomidae abundance were generally lower (mean r 2=.42). Zinc was negatively correlated with biotic metrics (r2=.23-.58). Values for EPT (r2=.60-.75) and species richness (r2=.54-.65) provided the highest correlation coefficients of the six metrics measured. Conductivity (r2=.18-.41) and pH (r2=.08-.21) showed the weakest correlations with biotic metrics. Streams affected by metal pollution also exhibited extreme habitat degradation due to activities involved in ore processing. As a result, macroinvertebrate communities may be severely impacted by habitat loss even where zinc concentrations are relatively low