1. University of Koblenz‐Landau, Institute of Integrated Natural Science, Geography, Universitätsstraße 1, 56070 Koblenz, Germany
2. Max Planck Institute of Biogeochemistry, P.O. Box 100164, 07701 Jena, Germany
3. University of Berne, Institute of Geography, Hallerstrasse 12, 3012 Bern, Switzerland