Abstract
Säkylän Pyhäjärvi (SW Finland) is an example of a large and shallow lake suffering from eutrophication. During the last 20 years, the quality and general usability of water in Pyhäjärvi have shown considerable variation driven by both a variety of human activities and climate-related factors such as wet and dry years. The lake has been thoroughly studied for decades and has been the object of comprehensive restoration activities both in the catchment and in the lake since the 1990s. Large variety of water protection measures like wetlands, sedimentation ponds and filtering systems have been implemented in the catchment area to reduce external nutrient load. Another important tool for Pyhäjärvi restoration is biomanipulation, done by local commercial fishermen in winter. Twenty-five percent of the annual phosphorus input is removed with fish catch. Currently, restoration work is facing new challenges: short or even nearly missing ice cover period and increased winter time nutrient load from the catchment. In the 2000s, there were 3 years with exceptionally short ice period, allowing only brief winter seining periods. Consequently, the biomanipulation catch was very low in 2007 and 2008 leading to observable food web effects. Phosphorus load was especially high in winters 2006/2007 and 2008/2009. On the basis of the data of 1987–2008, we have tested the hypothesis if climate-related winter time variables like phosphorus load, air temperature and precipitation would affect the water quality of the lake in following summer, here measured as chlorophyll a concentration in the lake water. A linear model has been used and a validation procedure has been performed to select the best variables. Our results indicate some of the linkages between climate-related catchment processes and the ecological status of the lake.
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Acknowledgments
The phytoplankton samples (1992–2005) were analysed by Kristiina Vuorio (1992–2005) and Sanna Kankainen (2006–2008) and zooplankton (1989–2008) by Vesa Saarikari. We thank local fishermen and Pyhäjärvi Fishing Area for providing the good collaboration in fish and fisheries monitoring. The research has been part of the project Changing Bothnian Sea funded by European Regional Development Fund and it has also been funded by Pyhäjärvi Protection Fund.
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Guest editors: T. Blenckner, T. Nöges, L. Tranvik, K. Pettersson, R. Naddafi / European Large Lakes II. Vulnerability of large lake ecosystems - Monitoring, management and measures
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Ventelä, AM., Kirkkala, T., Lendasse, A. et al. Climate-related challenges in long-term management of Säkylän Pyhäjärvi (SW Finland). Hydrobiologia 660, 49–58 (2011). https://doi.org/10.1007/s10750-010-0415-4
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DOI: https://doi.org/10.1007/s10750-010-0415-4