Biodiversity of chironomid fauna in mountain lakes and streams influenced by acidification and recovery from acidification.

This thesis examines the influence of acidification on the largest group of macroinvertebrates in mountain lakes and running waters - chironomids. The diversity of chironomids has been associated with temperature, the concentration of dissolved oxygen in the water, the amount of nutrients, and also with the ability to survive in conditions (e.g. extreme pH) that are not suitable for other taxa. Because of this the family Chironomidae has become a dominant group of macrozoobentos in many assemblages affected by acidification. The Bohemian Forest lakes and the Tatra Mountain lakes belong to the most frequently studied locations, which were affected by acidification. The peak of acidification was in the 1980s. It turned out that, during the acidification, the number of chironomids changed and also the species composition of their assemblages. The main reason was a change of trophic status, which chironomids reflected more than a change of pH. A decrease in the number of species occurred after the pH dropped below 5. Until then, only their relative abundance had been affected. Chironomids are also influenced by the toxic effect of Al. The most important factor affecting chironomids fauna is not the value of pH, but the change of food supply. Acid stream food webs are often viewed as being..