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

Diversity and biotic indices are often used to asses freshwater quality. Ho wever, few studies have been made of their applicability to mining-derived impact. Biotic indices, in particular, are problematic in this respect beca use they are devised for specific types of pollution (usually organic). Thu s, caution is required when using them in streams contaminated by other cla sses of pollutants. This study evaluates the performance of several diversi ty and biotic indices in rivers affected by coal mining in northwestern Spa in. The relation between them and a set of environmental variables has been determined by means of correlation (Pearson correlation coefficient). Acco rding to the correlation analysis, the variables most related to the biolog ical parameters were by far those indicating mining impact (sulfate and con ductivity). In general, the rest of the variables (nitrate, orthophosphate, chloride, distance from the source, among others) were not significantly c orrelated with th e biological indices. BMWP' (a Spanish version of the BMW P) and family richness of Ephemeroptera, Plecoptera and Trichoptera (EPT fa mily richness) were the indices most succesful in detecting mining impact, as shown by their high correlation with conductivity and sulfate. ASPT' (de rived from BMWP'), the Shannon index and family richness were of lesser ind icative value. These results suggest that some biotic indices may be a usef ul tool for monitoring water quality in rivers receiving coal mine drainage . BMWP', in particular, could be a good starting point for devising a bioti c index specific to this type of pollution.