| Summary: | Heavy metals are of great concern when released into the environment, especially at high concentrations. Because of their persistence and toxicity, they have the ability to impact organisms both directly and indirectly via bioaccumulation in the food chain. In this report the effects on aquatic insect composition and abundance as well as possible effects on metamorphosis from larvae to adults were examined in six lakes – three with elevated Zn and Pb concentrations and three reference lakes - situated in Arjeplog municipality. Aquatic larvae and adult aquatic insects were sampled one year apart, and the number of individuals and community composition of both life stages were compared. Contrary to my hypothesis, the results showed no significant differences in abundance, taxa richness or number of individuals in pollution sensitive taxa (EPT) due to contamination. However, the result showed that the effect of contamination on the number of insects is different at different life stages (larval or adult), with fewer adults than expected emerging from contaminated lakes. This is likely explained by detrimental effects, caused by high metal concentrations, obstructing metamorphosis and decreasing emergence success. In this study, the negative effects on emergence could foremost be observed in chironomids (Chironomidae), which was the most abundant insect taxon in both reference and contaminated sites. This leads to the conclusion that including effects on metamorphosis can provide useful insights when assessing effects of a contaminant on the health of freshwater ecosystems.
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