Influence of drainage from old mine deposits on benthic macroinvertebrate communities in central Swedish streams

We analysed the benthic macroinvertebrate species composition, taxonomic richness (as expected richness for 100 individuals), total abundance and biomass at 117 stream sites in the province of Dalarna. Partial least squares regression models were constructed from observations on undisturbed sites and used to predict these community parameters at sites exposed to elevated levels of copper, zinc, lead and cadmium resulting from leakage from old mine deposits. Species richness at undisturbed sites was positively related to the size of the catchment, pH, channel width, calcium concentration and the proportion of deciduous trees in the riparian zone. In streams with elevated metal concentrations, we found reductions in taxonomic richness for total macroinvertebrates, mayflies, stoneflies and combined EPT (Ephemeroptera, Plecoptera and Trichoptera), but not for that of Trichoptera nor total abundance or biomass. Copper and zinc were those metals showing strongest negative associations with richness. Some taxa, common at undisturbed sites, were missing at metal-polluted sites. These taxa were the mayflies Ameletus inopinatus, Ephemerella aurivilli and Heptagenia dalecarlica, the stonefly Protonemura meyeri and the caddisfly Apatania sp.