1. Department of Aquatic Ecology and Centre for Water and Environmental Research (ZWU), University of Duisburg-Essen, D-45141 Essen, Germany
2. Process Engineering Group, Spanish Council for Scientific Research, IIM-CSIC, 36208 Vigo, Spain
3. Department of Environmental Science, Faculty of Science, Radboud University Nijmegen, 6525 HP Nijmegen, The Netherlands