1. National Water Quality Laboratory, U.S. Geological Survey, P. O. Box 25046 MS407, Denver Federal Center, Denver, Colorado 80225-0046, Branch of Regional Research − Central Region, U.S. Geological Survey, P. O. Box 25046 MS408, Denver Federal Center, Denver, Colorado 80225-0046, and Department of Animal Science and Industry, Kansas State University, Manhattan, Kansas, 66506