1. University of Helsinki, Faculty of Biological and Environmental Sciences, Ecosystems and Environment Research Programme, Lammi Biological Station, Pääjärventie 320, Lammi FI-16900, Finland
2. University of Jyväskylä, Department of Biological and Environmental Sciences, P.O. Box 35, Jyväskylä FI-40014, Finland
3. University of Eastern Finland, Department of Environmental and Biological Sciences, P.O. Box 1627, Kuopio FI-70211, Finland
4. Tampere University of Technology, Laboratory of Chemistry and Bioengineering, P.O. Box 541, Tampere FI-33101, Finland