Relationship between benthic assemblage structure and coal mining in the Boeza River basin (Spain)

Abstract

Three rivers from northwestern Spain were sampled in a two-year survey. Two aspects of the assemblage were considered: taxon richness and taxonomical composition. The latter was analysed by Canonical Correspondence Analysis (CCA). Relative frequencies of taxa at each site were also used to provide a complete view of the tolerance of the groups. CCA revealed mining as one of the main factors conditioning the faunal composition together with the distance from the source. Richness decreased at impacted sites and was negatively correlated with variables indicating mining pollution (conductivity, sulfate, silt accumulation and some metals, among others). Oligochaeta, Nemouridae, Leuctridae, Dytiscidae, Limoniidae, Chironomidae and Ceratopogonidae appeared to be the groups most tolerant to this type of pollution. Other taxa could also stand a moderate pollution. On the other hand, Chloroperlidae, Perlodidae, Philopotamidae, Leptophlebiidae, Goeridae and Blephariceridae were the most sensitive families. Although the tolerance levels of the taxa to mining and their BMWP' biotic index scores were closely related, some divergences were evident. In particular, some of the most tolerant families in this study (Leuctridae, Nemouridae and Rhyacophilidae) had high BMWP' scores. The scores of at least some of the families should be adapted if this biotic index is to be used in the assessment of coal mining pollution.