Performance of some diversity and biotic indices in rivers affected by coal mining in northwestern Spain

Abstract

Diversity and biotic indices are often used to asses freshwater quality. However, few studies have been made of their applicability to mining-derived impact. Biotic indices, in particular, are problematic in this respect because they are devised for specific types of pollution (usually organic). Thus, caution is required when using them in streams contaminated by other classes of pollutants. This study evaluates the performance of several diversity and biotic indices in rivers affected by coal mining in northwestern Spain. The relation between them and a set of environmental variables has been determined by means of correlation (Pearson correlation coefficient). According to the correlation analysis, the variables most related to the biological parameters were by far those indicating mining impact (sulfate and conductivity). In general, the rest of the variables (nitrate, orthophosphate, chloride, distance from the source, among others) were not significantly correlated with th e biological indices. BMWP' (a Spanish version of the BMWP) and family richness of Ephemeroptera, Plecoptera and Trichoptera (EPT family richness) were the indices most succesful in detecting mining impact, as shown by their high correlation with conductivity and sulfate. ASPT' (derived from BMWP'), the Shannon index and family richness were of lesser indicative value. These results suggest that some biotic indices may be a useful tool for monitoring water quality in rivers receiving coal mine drainage. BMWP', in particular, could be a good starting point for devising a biotic index specific to this type of pollution.