APPLIED ISSUES Species‐ and population‐specific responses of translocated hydropsychid larvae (Trichoptera, Hydropsychidae) to runoff from acid sulphate soils in tin River Kyrönjoki, western Finland

Abstract

SUMMARY1. The effects of runoff from acid sulphate soils on Hydropsyche angustipennis, H. siltatai and Ceratopsyche nevae larvae were studied. H. angustipennis occurs in both contaminated and uncontaminated rivers, whereas H. siltalai and C. nevae occur only in uncontaminated rivers. Larvae were translocated in PVC‐tubes to contaminated sites. Larvae returned to an uncontaminated river were used as a control.2. Heavy larval mortality and a high incidence of morphological abnormalities were observed in larvae translocated to the contaminated, acid dyers. In the control river pH remained near 6 and no larval mortality or morphological abnormalities were observed. In the most contaminated river nutrient concentrations, amount of organic matter and pH increased substantially after the flood.3. Mortality and incidence of abnormalities were significantly higher in H. siltalai and C. nevae than in H. angustipennis. As metal concentrations decreased and pH increased, the larvae of all species developed normally, except in the most contaminated river, where only H. angustipennis appeared to tolerate the increasing load of nutrients and organic matter.4. Reciprocal translocation of H. angustipennis larvae between contaminated and uncontaminated rivers revealed significant differences in larval development and the occurrence of abnormalities among sites and populations. At both sites, larvae originating from the contaminated site grew more slowly than did larvae from the uncontaminated site. Morphological abnormalities were detected only in H. angustipennis larvae translocated from the uncontaminated to the contaminated site.5. The results suggest that species‐specific differences in sensitivity to acidification, metal contamination and eutrophication are the major determinants of hydropsychid guild structure in the River Kyrönjoki. Further, population‐specific differences in growth and occurrence of morphological abnormalities in the H. angustipennis larvae may reveal either phenotypic adaptation or evolution of resistance to runoff from acid sulphate soils.