1. Leibniz Inst. of Freshwater Ecology and Inland Fisheries; Müggelseedamm 301 DE-12587 Berlin Germany
2. Witteveen+ Bos Consulting Engineers, Ecology group; PO Box 233 NL-7400 AE Deventer the Netherlands
3. Dept of Aquatic Ecology, Netherlands Inst. of Ecology (NIOO-KNAW); Droevendaalsesteeg 10 NL-6708 PB Wageningen the Netherlands
4. KWR Watercycle Research Inst.; PO Box 1072 NL-3430 BB Nieuwegein the Netherlands