Abstract
The speciation of mercury was studied with respect to (a) dissolved atomic mercury, (b) dissolved ionic mercury, and (c) total mercury in two dimictic lakes of North-East Germany. Differential pulse anodic stripping voltammetry was used for the analyses. The results show that biological processes dominate the speciation. They are responsible for high concentrations of atomic mercury and also organomercury compounds. The oxidation of atomic mercury under environmental conditions in lake water is very slow, so that the equilibrium between Hgaq° and Hgaq and Hgaq 2+ can only be established during long periods of decreased bioactivity, as in wintertime. The sedimentation of the detritus during summer leads to a very pronounced decrease of the overall mercury in the entire water body of the lakes.