The BIOLA model
A 1D biogeochemical lake model has been developed at SMHI (Pers, 2003). The purpose was to simulate an eutrophied lake regarding nutrient concentrations and algal biomass in the vertical. The model can be used with changing nutrient supply or other management scenarios to study the effect on the lake. The nutrient concentration and the biological variables may change in response to changing nutrient supply. For example, phytoplankton growth is regulated by nutrient concentration, but they are also regulated by grazing zooplankton. The model is based on general process equations and other lake models found in literature (Pers, 2002).
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The model includes 14 state variables (Fig. 1), including inorganic nutrients in the water and in the sediment, biological variables, organic matter in the water and in the sediment, and oxygen. It is based on established process descriptions, which transforms carbon, phosphorus and nitrogen in lakes. The model simulates the changes during the year in nutrient concentration and in biological variables. Important processes included in the model are; algal growth, zooplankton grazing, decomposition of organic material, exchange of nutrients with the sediments, denitrification (Fig. 1). BIOLA is based on the equation solver PROBE and is therefore vertically distributed and describes the variation of the variables with depth. It is fed by inflow to the lake and with observed weather data, which decide the physical variables and the mixing of the lake. BIOLA is supplied with nutrients etc. from inflow, atmospheric deposition and other sources. A large number of coefficients has been gathered from the literature (Pers, 2002) to estimate appropriate parameter interval for calibration. The model has been applied to Lake Ringsjön (Fig. 2; Pers, 2005), Lake Glan and Lake Vänern (Pers and Persson, 2003; Dahl and Pers, 2004).
Figure 2. Time series of observed and modelled DIN and phytoplankton concentration in Lake Västra Ringsjön.
Ahlkrona, M., 2002. Phosphorus in a Biogeochemical Lake Model. Report RH 17, SMHI, Norrköping.
Dahl, M. and B.C. Pers, 2004. Comparison of four models simulating phosphorus dynamics in Lake Vänern, Sweden. Hydrology and Earth System Sciences, 8(6):1153-1163.
Pers, B.C., 2002, Model description of BIOLA - a biogeochemical lake model (including literature review), Report RH 16, SMHI, Norrköping.
Pers, B.C., 2003, BIOLA Biogeochemical Lake Model Manual, Report Hydrologi 91, SMHI, Norrköping.
Pers, B.C., and Persson, I., 2003. Comparison of a biogeochemical lake model in different lakes. Nordic Hydrology, 34(5):543-558.
Pers, B.C., 2005, Modeling the Response of Eutrophication Control Measures in a Swedish Lake. Ambio, 34(7):552-558.