Primary production, mineralization, and sedimentation in the euphotic zone of two Swiss lakes

Phosphorus and nitrogen concentrations, phytoplankton, bacteria, detritus, primary production, and sedimentation have been investigated over a year in two Swiss lakes of different trophic state. Inflow and outflow of the lakes were calculated, as well as the eddy diffusion of P and N from the metalimnion into the epilimnion, and from these data a balance of the epilimnetic phosphorus and nitrogen cycle was drawn up. Different methods of calculation all suggested a high intensity of the internal nutrient cycle in the epilimnion. By means of autolysis, destruction, and excretion, about 35–75% of the nitrogen and 55–85% of the phosphorus needed for the measured primary production can thus be regenerated.