Responses of insects, especially Chironomidae (Diptera), and mites to 130 years of acidification in a Scottish lake

A study in Round loch of Glenhead, southwest Scotland, showed that 130 years of anthropogenic acidification caused successively decreased stability, diversity, productivity and survival rate of the non-biting midge, mayflies, caddis-flies and water mites. The earliest known evidence of anthropogenic acidification on bottom fauna occurred around 1850 when a drop in the lake's pH was first indicated by decreased stability and changes in species composition of chironomids and mayflies in the littoral zone. Major changes in the profundal chironomid fauna did not occur until about 1950 when mean lake pH dropped below 5.0. This caused the littoral fauna to become even more unstable and the first significant elimination of species occurred. The 12 most frequently encountered species before 1850 were still present during 1950-90 although some of them were in low numbers. All 12 species were common and often dominated in oligotrophic lakes with a pH of 6.5-7. Common species of chironomids were more affected by lake trophic status than acidity and rare and less common chironomids were the most endangered when lakes acidified. There are 66 references.