Patrick L. Brezonik is Professor Emeritus of Civil Engineering at the University of Minnesota. His research interests are focused on natural aquatic systems, including nutrient cycling and chemistry, metal complexation by natural organic matter, and applications of remote sensing to aquatic systems. William A. Arnold is the Joseph T. and Rose S. Ling Professor in the Department of Civil Engineering at the University of Minnesota. His research interests are in the areas of transformation, transport, and remediation of anthropogenic chemicals in the environment, including surface-mediated oxidation/reduction reaction, photochemistry, and partitioning.