BIOGEOCHEMICAL MODELLING OF LAKE VÄNERN

Lake Vänern was modelled with the BIOLA model (Pers and Persson, 2002), with the purpose to improve the HBV-N model's retention of nitrogen in large lakes with long residences time, which was a weak point in the TRK system. The study indicates that it is the time for sedimentation that separates the large lakes from other lakes. In addition their sheer size give them a large influence, which make small errors in the model more visible.

The effect of nitrogen reducing measures for Lake Vänern was simulated with BIOLA. These scenarios showed that nitrogen from municipal waste water treatment plants, atmospheric deposition, and rural households did not have any significant effect on the algal biomass in Lake Vänern, but reducing the supply by tributaries slightly decreased the phytoplankton. By including and excluding retention of nitrogen in a Lake Vänern HBV-N simulation, it was found that the lake reduces the nitrogen transport to the sea by 15%. The nitrogen reducing effect of Lake Vänern were unaffected by reduced nitrogen load upstream.

The simulation of Lake Vänern resulted in a follow-up study comparing four different phosphorus models applied to Lake Vänern (Dahl and Pers, 2004). The study was performed together with Magnus Dahl at Karlstad University. The fit to observations was good for all models, except for BIOLA that was slightly worse. All models has their advantages, e.g. the simpler models are fast and easy to use, while the more complex models can handle more complex scenarios, e.g. nitrogen scenarios in BIOLA.

Duration: 2001-2003

Funded by: Swedish EPA, MISTRA (VASTRA)

Responsible at SMHI: Charlotta Pers

External partners: Magnus Dahl, Karlstad University

References

Dahl, M., and Pers, B.C., 2004. Comparison of four models simulating phosphorus in Lake Vänern, Sweden. Hydrology and Earth System Sciences, 8(6):x-x.

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., and Persson, I., 2002. Comparison of a biogeochemical lake model in different lakes. Proc. of the XXII Nordic Hydrological Conference, Røros, Norway, Vol.I:369-378.