Benthic Fauna of Extremely Acidic Lakes (pH 2 - 3)

Structure of the benthic invertebrate communities were investigated in terms of composition, abundance, and biomass from extremely acidic lakes with pH values from 2 to 3 in areas where coal was intensively mined in the Lusatian region in the eastern Germany. Benthic invertebrates colonisation on leaves and the breakdown rate processing of the leaf: birch, ash and walnuss were investigated. Chironomus crassimanus pupal exuvie (acid-resistant species) was described and the diet was investigated through analysis of their gut content. Ch. crassimanus is a pioneer and an opportunist species that have a large capacity to colonise in extreme habitats (pH-value from 2.1 to 3.0). It is a detritivore with collector- gatherers feeding habit, consuming mainly fungi, bacteria and algae associated to detritus in the lake sediments. The benthic food web in extremely acidic mining Lusatian lakes is very short in terms of species richness, trophic relationship, guilds and functional feeding groups. Shredders as Limnophyes minimus (Chironomidae) and Hydrozetes lacustris (Acari) occurred in low abundance in AML 107 and 111, and it may be in response to slow leaf breakdown process in these ecosystems, except in AML 117 where the H. lacustris contributed most to ecosystems functioning via the processing of litter. Aquatic insects are the top-predators of these ecosystems. They did not depend on the level of pH in the lakes, but on the availability of food resources. Therefore this ecosystem can be considered as bottom - up effect. Decomposers and their food resource are a main pathway for the benthic process in extremely acidic mining lakes. This system may be described as donor-controlled dynamics, in which the prey controls the density of the predators.