1. The Key Laboratory of Water and Sediment Sciences, Ministry of Education, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, P. R. China
2. State Key Laboratory of Estuarine and Coastal Research, East China Normal University, 500 Dongchuan Road, Shanghai 200241, P. R. China
3. Norwegian Institute for Water Research (NIVA), Thormølensgate 53D, N-5006 Bergen, Norway
4. Institute of Biology, Freie Universität Berlin, Altensteinstr. 6, D-14195 Berlin, Germany
5. Institute of Geological Sciences, Freie Universität Berlin, D-12249 Berlin, Germany
6. Norwegian Institute for Water Research (NIVA), Økernveien 94, Oslo N-0579, Norway