1. Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark
2. Department of Bioscience−Stream and Wetland Ecology, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark
3. Team Environmental Risk Assessment, Wageningen Environmental Research (Alterra), P.O.
Box 47 6700 AA Wageningen, The Netherlands