A MATHEMATICAL-MODEL OF THE MANGANESE CYCLE IN A SEASONALLY ANOXIC LAKE

The processes controlling the Mn cycle in a seasonally anoxic lake (Greifensee, Switzerland) were simulated with a dynamic one-dimensional vertical lake model (CHEMSEE). The chemical parameters comprised Mn(II), particulate Mn, and oxygen concentrations and the processes included in the calculations were the Mn(II) flux from the sediment, Mn(II) oxidation, and particulate Mn removal from the water column. Field data from Greifensee obtained in 1988 and 1989 were used to determine the validity of the model and to estimate the rate constant values for the processes. Optimal values of the rate constants were determined by comparison of simulated results with field data and were in general agreement with literature values. The Mn(II) flux from the sediment exhibited similar seasonal variations in 1988 and 1989. The results show that it is possible to model the Mn cycle in a dynamic system and highlight the necessity of accurately determining the rate laws of the important processes and their relationships to the oxygen content of the waters.