MODELLING NUTRIENT FLUXES IN LAKES

This project is a part of the Swedish Water Management Research Programme, VASTRA. In lakes the phytoplankton production is a result of the nutrient conditions of the lake. A 1D biogeochemical lake model (called BIOLA), which simulates nutrients, algae, sediment etc. in eutrophic lakes has earlier been developed within Vastra (Pers, 2003; Pers, 2002; Ahlkrona, 2002). The model has been applied to three lakes, the result of which are compared in Pers and Persson (2003). In this project BIOLA is used for scenario simulations, e.g. decreased concentration of nutrients in inflow, sediment manipulation and biomanipulation through planktivouros fish reduction (Figure 1; Pers, 2005).

Several parameters were calibrated, but there was still some difficulties with the phosphorus modelling, which indicate that further model development is nescessary. The lake showed the most favourable development for the scenarios with nutrient load reduction and biomanipulation. Reduction of both nitrogen and phosphorus loads had larger effect on the lake status than reducing either phosphorus or nitrogen. Inorganic nitrogen reduction reduced nutrient (phosphate) mineralisation by reducing denitrification, while reduction of total phosphorus load reduced the organic material available for degradation.

Figure 1 (clicking opens larger version in a new window)
Result from different nutrient reductions scenarios simulated with BIOLA in Lake Ringsjön. Annual mean phytoplankton (algae and cyanobacteria) concentration (mg C/L) in Lake Östra Ringsjön.