1. Aquatic Ecology and Water Quality Management Group, Department of Environmental Sciences, Wageningen University, P.O. Box 8080, 6700 DD Wageningen, The Netherlands, The Netherlands Organization for Applied Scientific ResearchEnvironment, Energy, and Process Innovation (TNO-MEP), P.O. Box 342, 7300 AH Apeldoorn, The Netherlands, and The Netherlands Organization for Applied Scientific ResearchEnvironment, Energy, and Process Innovation (TNO-MEP), P.O. Box 57, 1780 AB Den Helder, The Netherlands