CLIMATE CHANGE EFFECT ON NITROGEN TRANSPORT AND ALGAL GROWTH

This project focused on the most important processes regulating the amount of nitrogen transported from land; arable-soil leaching, water discharge and nitrogen retention. In addition, the eutrophication problem with high algal-concentrations was explored for one lake with respect to a future climate. The aim was to quantify the expected changes of nitrogen flow and algal growth, by applying the SWECLIM climate-change scenarios on the VASTRA tools and pilot catchment in southern Sweden.

The project was a co-operation between the two MISTRA programmes SWECLIM and VASTRA. SWECLIM contributed with the climate change scenarios, down-scaling procedures and the transformation function for hydrological applications. VASTRA contributed with modelling tools for water quality estimations and input data for the pilot catchment Rönne å in southern Sweden.

For nitrogen transport from land to sea, the TRK concept was applied in the scenarios, so that the results easily can be compared with the calculations (based on the present climate) on behalf of the Swedish Environmental Protection Agency. Changes in water balance as a consequence of climate change was calculated by applying the scaling methodology as used in SWECLIM when transforming RCA output to HBV input. The single largest anthropogenic source of nutrients to fresh-water is arable-land leaching (about 40% on a national level). In this project (Arheimer et al., 2005) this was simulated with the SOILNDB model. The overall impact on nitrogen transport from land to sea was evaluated by using the HBV-N model.

The combined hydrodynamic PROBE - biogeochemical BIOLA model was used to simulate the change of lake stratification and water quality due to weather, inflow, outflow and processes in Lake Ringsjön. The climate change impact study gave a warmer lake with less ice-days. For some scenarios the stratification increased. All climate scenarios gave higher productivity in the lake, but algae sometimes decreased in concentration when the higher production increased zooplankton, i.e. grazing. For most pelagic variables modelled in the climate change scenarios, the effect of changed meteorological forcing dominated over the effect of changed changed water flow and nutrient load (Arheimer et al., 2005). The only exception being inorganic nutrients.

Figure 1 (clicking opens larger version in a new window)
Total phytoplankton (algae and cyanobacteria) with BIOLA in Lake Västra Ringsjön for different climate scenarios. Black line is simulation of present conditions, red dots mean monthly observations for several years, and blue lines are simulations with different climate change assumptions/models

Deliverables: The results will be presented in two papers with the following content:

• Climate change impact on nitrogen load, retention and source apportionment

• Climate change impact on algal growth in Swedish lakes

Duration: 2002-2003

Funded by: MISTRA

Responsible at SMHI: Berit Arheimer

External partners: SLU (Swedish University of Agricultural Sciences)

References

Andréasson, J., B. Arheimer, S. Fogelberg, H. Johnsson, K. Mårtensson, C. Pers, K. Persson and J. Rosberg, 2003. Expected changes in nitrogen transport and algal growth due to climate change. Final Report to SweClim.

Arheimer, B., J. Andréasson, S. Fogelberg, H. Johnsson, K. Mårtensson, C. Pers, K. Persson and J. Rosberg, 2004. Climate change impact on water quality - model results from southern Sweden. Proceedings of Regional-scale climate modelling Workshop in Lund 19 Mars - 2 April 2004. Lund Electronic Report in Physical Geography Nr X.

Arheimer, B., J. Andréasson, S. Fogelberg, H. Johnsson, C. Pers and K. Persson, 2005. Climate Change Impact on Water Quality: Model Results from Southern Sweden. Ambio, 34(7): 559-566.

Pers, B.C., 2004. Climate change effect simulated with a lake model. Proc. of the 8th European Workshop on Physical Processes in Natural Waters, Lund, 29 August - 1 September 2004. Eds. L. Begtsson and O.A. Maher, pp: 127-138.