1. U.S. Geological Survey, 431 National Center, Reston, Virginia 20192, Max-Planck-Institute for Biogeochemistry, Beutenberg Campus, P.O. Box 100164, 07701 Jena, Germany, UFZ Umweltforschungszentrum Leipzig-Halle GmbH, Labor für Stabile Isotope, Permoserstrasse 15, 04318 Leipzig, Germany, Isotope Hydrology Laboratory, International Atomic Energy Agency, P.O. Box 100, A-1400 Vienna, Austria, Centrum voor Isotopen Onderzoek (CIO), Rijksuniversiteit Groningen, Nijenborgh 4, 9747 AG Groningen, Netherlands,...