Affiliation: | Limnological Institute, University of Konstanz D-78457, Konstanz, Germany tel: +49 7531 88-3364; fax: +49 7531 88-3533; e-mail: Dietmar.Straile{at}uni-konstanz.de UFZ-Centre for Environmental Research, Institute for Inland Water Research Magdeburg, D-39104, Magdeburg, Germany |