IMPACTS OF ENVIRONMENTAL SCENARIOS ON CHLOROPHYLL-ALPHA IN THE MANAGEMENT OF SHALLOW, EUTROPHIC LAKES FOLLOWING BIOMANIPULATION - AN APPLICATION OF A NUMERICAL-MODEL

Accurate prediction of species changes in lake ecosystems following bi omanipulation measures is of paramount importance in view of water qua lity management. The temporal variation of phytoplankton biomass as ch lorophyll-a and transparency as Secchi depth measurements are studied in the Lake Bleiswijkse Zoom, The Netherlands, with a comprehensive st ructural dynamic model. In the formulation of the biological model, ph ytoplankton as several species, zooplankton, detritus, planktivores an d benthivores, and piscivores are considered to be major contributing state variables for the model. The primary goal of this paper is to de scribe the possible impacts of several environmental scenarios on chlo rophyll-a biomass qualitatively as it would help lake and environmenta l managers and relevant authorities elucidate the processes of eutroph ication and biomanipulation in a broad way. Some of the scenarios that have been studied by this model are: (1) The effect of fixed stoichio metry in terms of internal nitrogen and phosphorus that are tied up wi thin algal cells; (2) the effects of external phosphorus limitation; ( 3) light limitation and external nitrogen limitation on algal growth; (4) probable consequences that have taken place within the chlorophyll -a biomass due to change in biomasses of various aquatic organisms; an d (5) possible changes of chlorophyll-a biomass due to higher temperat ures caused by global warming.