1. Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dubendorf, Switzerland.
2. Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, 8092 Zurich, Switzerland.
3. Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, St. Paul, MN 55108, USA.
4. Institute of Groundwater Ecology, Helmholtz Zentrum Munchen, 85764 Neuherberg, Germany.