The model BIOLA, developed at SMHI, is a model for simulating the temperature and water quality of a lake. BIOLA simulates the lake as a water column, but several lake basins can be coupled to each other.

Description and purpose

The model is based on the equation solver PROBE that calculates the mixing and temperature stratification in a lake. BIOLA simulates the nutrient transformation in eutrophic lakes, and give result in the form of vertically distributed nutrient concentrations and phytoplankton biomass etc. The model can be used to simulate the effect of changed nutrient load to a lake and the effect on a lake of other measures for better water quality.

The model is based on process flows (e.g. phytoplankton growth, zooplankton grazing, degradation of organic material, nutrient exchange with sediment, denitrification) with equations found in literature (Pers, 2002). The model comprises 14 state variables: inorganic nutrients in lake water and in sediment, biological variables (phytoplankton, zooplankton, macrophytes, fish), organic material in lake water and sediment, and oxygen.

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Figure 1. Simplified structure of the BIOLA model. Enlarge Image

Necessary information

The model is forced with time series of nutrient load (inflow, point sources, and atmospheric deposition) and meteorology (air temperature, wind, cloudiness, and relative humidity). The latter time series determine the physical conditions of the lake, i.e. mixing, temperature and stratification. In addition, information about the lake depth and light conditions are needed.

The model is calibrated against observations. For this time series of nutrients and phytoplankton are necessary, and, if available, zooplankton and organic material can also be used. For validation similar time series for another time period or lake basin are used and also other data from studies in the lake if available.

Practical experience

BIOLA has so far simulated four Swedish lakes (Pers and Persson, 2003; Dahl and Pers, 2004; Pers, 2005, Pers and Blenckner, 2006). A manual has been published (Pers, 2003).

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Figure 2. Example of result from simulations in Lake Västra Ringsjön, southern Sweden. Simulated and observed lake mean concentrations of dissolved inorganic nitrogen (DIN) and phosphate (PO4). Enlarge Image


  • 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, SMHI Hydrologi Nr 91, Norrköping.
  • Pers, B.C., 2005, Modeling the Response of Eutrophication Control Measures in a Swedish Lake. Ambio, 34(7):552-558.
  • Pers, C., and T. Blenckner, 2006. Lake responses to modelled climate change - The example of the Swedish Lake Erken, I: Proceedings of the XXIV Nordic Hydrological Conference 2006, Eds: J.C. Refsgaard and A.L. Höjberg, NHP Report No. 49, 617-624.
  • Pers, B.C., and I. Persson, 2003. Comparison of a biogeochemical lake model in different lakes. Nordic Hydrology, 34(5): 543-558.