The Influence of Nutrient Availability on the Ecosystem Behaviour of a Salt Water Lake

Abstract

The influence of the availability of silicon, nitrogen and phosphorus on the behaviour of the ecosystem in the salt Lake Grevelingen is evaluated. Quantification of the nutrientcycling is essentially based on a dynamic calculation of detritus formation resulting from mortality of phytoplankton and microphytobenthos, including mineralization as function of temperature and substrate concentration. Also changes of the dissolved inorganic nutrientpools resulting from primary production, mineralization and net loading are dynamically ca1culated. Silicon and nitrogen are reversibly fixed in bottomdetritus during the summer halfyear, which implies that primary production depends on the balance between accumulation of detritus in the bottom and mineralization. In contrast the dynamics of phosphorus depend only to a minor extent on primary production and net loading. The net yearly load of nitrogen equals the amount of nitrogen present in the waterphase during the winterperiod. However winter concentrations do not increase and nitrogen remains a limiting factor for primary production. 3-4 g N/m2/year is apparently removed from the lake by denitrification. The environmental factors enabling denitrification are important for consolidation of the ecosystem behaviour. From a management point of view stratification which inhibits denitrification, should be avoided.