1. US Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Mid-Continent Ecology Division, 6201 Congdon Boulevard, Duluth, MN 55804, USA.
2. Inland Waters Institute, 29 Powers Drive, Herring Cove, NS B3J 2P8, Canada.
3. Natural Resources Research Institute, University of Minnesota – Duluth, 5013 Miller Trunk Highway, Duluth, MN 55811, USA.