1. School of Public and Environmental Affairs and Department of Chemistry, Indiana University, Bloomington, Indiana 47405, Centre for Atmospheric Research Experiments, Atmospheric Environment Service, RR#1, Egbert, Ontario, Canada L0L 1N0, National Water Research Institute, Canada Centre for Inland Waters, P.O. Box 5050, Burlington, Ontario, Canada L7R 4A6, and Illinois State Water Survey, 2204 Griffith Drive, Champaign, Illinois 61820