Resultat och påverkan

The main object of the REFLECT project was to study the effects of climate and weather conditions on freshwater lakes in different regions of Europe. Altogether partners from 7 European countries were involved in the study. In the Finnish project large efforts were put into the collection and analysis of historical data series from the two study sites, Lake Pääjärvi and Lake Valkea-Kotinen and their catchments. The analysis of these time-series was completed in 2000. At the same time monitoring of lakes, catchments and local weather conditions continued at varying frequency through the project. To conclude, our results indicate that weather conditions, and especially precipitation, may have a major impact on the leaching of nutrients from the catchments in northern Europe. Due to this,lakes with short retention times are likely most vulnerable to changes in organic matter, nitrogen and phosphorus concentrations because of the abiotic reasons. No simple relationship between long-term da ta sets of phytoplankton and climatic variables were found in the Finnish study lakes. However, if the future climate becomes warmer the productivity of L. Pääjärvi may increase. The secondary site was especially sensitive to changes in weather conditions, particularly in spring after the ice break-up, which indicates that icreased air temperature in spring may increase a potential for meromixis in sheltered small boreal brown-water lakes. In general, environmental factors such as agriculture, forestry, and other extensive land-use practices should be considered, when the effects of climate change on boreal lake ecosystems will be evaluated. Julkaisut: Arvola, L., Järvinen, M., Virta, J., Elo, A.-R. & Leppäranta, M. 1998. Responses of European freshwater lakes to environmental and climatic change (REFLECT). An extended abstract, 2nd International conference on climate and water, Espoo, Finland, 17-20 August 1998. Arvola, L., Palomäki, A., Lehtinen, S. & Järvinen, M. 2002. Phyto plankton community structure and biomass in two basins of a boreal lake in relation to local weather conditions and North Atlantic oscillation. Verh. Int. Verein. Limnol. 28:700-704. Arvola, L., Hakala, I., Järvinen, M., Huitu, E. & Mäkelä, S. 2002. Effects of weather conditions on water quality in two small boreal rivers. Arch. Hydrobiol. Suppl. 141/3-4:195-208. George, D.G., Järvinen, M. & Arvola, L. 2003. The influence of the North Atlantic Oscillation on the winter characteristics of Windermere (UK) and Pääjärvi (Finland). Bor. Env. Res. (submitted). Jasser, I. & Arvola, L. 2002. Effects of abiotic factors on the abundance of autotrophic picoplankton in four boreal lakes. J. Plankton Res. Jasser, I. & Arvola, L. 2002. Seasonal coupling of autotrophic picoplankton and phytoplankton in three boreal lakes. Verh. Int. Verein. Limnol. 28: 190-193. Järvinen, M., Rask, M., Ruuhijärvi, J. & Arvola, L. 2002. Temporal coherence in water temperature and chemistry under the ice of boreal lakes (Finland). Water Research 36: 3949-3956. Kärkäs, E. 2000. Ice climatology of Lake Pääjärvi. Geophysica 36(1-2):85-94. Lehtinen, S. 2000. Kasviplanktonin ajallinen vaihtelu Lammin Pääjärvessä (Temporal variation of phytoplankton in Lake Pääjärvi). M.Sc. thesis, Dept. Ecology and Systematics, Univ. Helsinki. 70 p. (in Finnish). Leppäranta, M. & Kosloff, P. 2000. The structure and thickness of Lake Pääjärvi ice. Geophysica 36(1-2): 233-248. Uusikivi, J. 2000. Seasonal evolution of the ice conditions in Lake Pääjärvi. M.Sc. thesis, Dept. Geohysics, Univ. Helsinki. Virta, H. 2000. Tuulipussin aiheuttaman kumpuamisen dynamiikka Lammin Pääjärvessä (Dynamics of wind induced upwelling in L. Pääjärvi). M.Sc. thesis, Dept. Geophysics, September 2000, Univ. Helsinki.