1. Swedish University of Agricultural Sciences, Department of Environmental Assessment, P.O. Box 7050, SE-750 07 Uppsala, Sweden
2. USDA-ARS, Soil and Water Management Research Unit, Department of Soil, Water and Climate, 1991 Upper Buford Circle Room 439, St. Paul, Minnesota 55108
3. Chemistry Department, College Misericordia, Dallas, Pennsylvania 18612
4. Department of Soil, Water, and Climate, University of Minnesota, St. Paul, Minnesota 55108