1. University of Utah, Civil and Environmental Engineering, Energy and Geoscience Institute, 421 Wakara Way, Suite 125, Salt Lake City Utah 84108, Finnigan MAT GmbH, Postfach 1401, D-28088 Bremen, Germany, Department of Analytical and Environmental Chemistry, University of Ulm, D-89069, Ulm, Germany, and Bodega Bay Institute, The Bodega Bay Institute, 2711 Piedmont Avenue, Berkeley, California 94705