1. Department of Freshwater Ecology; Alterra, Wageningen University and Research Centre; P.O. Box 47 6700 AA Wageningen The Netherlands
2. Department of Soil and Water Conservation and Organic Waste Management; Centro de Edafología y Biología Aplicada del Segura, CSIC; P.O. Box 164 30100 Murcia Spain
3. Wageningen University and Research Centre; P.O. Box 47 6700 AA Wageningen The Netherlands
4. Department Statistical Analysis; Biometris, Wageningen University Research; P.O. Box 47 6700 AA Wageningen The Netherlands
5. Institute for Biodiversity and Ecosystem Dynamics (IBED); University of Amsterdam; P.O. Box 94248 1090 GE Amsterdam The Netherlands