MATHEMATICAL-MODEL FOR THE ECOSYSTEM RESPONSE OF LAKE-LADOGA TO PHOSPHORUS LOADING

The ecosystem response model described in this paper combines an ecosy stem model and a three-dimensional circulation model of lake Ladoga de veloped earlier by the authors. The ecosystem model describes the proc ess of Lake Ladoga eutrophication, and its biological submodel describ es changes in the phyto- and zooplankton. In the earlier model version , lake circulation was determined using a two-dimensional hydrodynamic al model which was not completely adequate. The present model allows c alculation of the distributions of phyto- and zooplankton and mineral phosphorus and nitrogen. One of its main advantages is that reliable c omputations of the ecosystem dynamics over an extended period of time are possible. The response of the ecosystem to different levels of pho sphorus pollution loading and to weather conditions is studied.