1. Institute of Freshwater Ecology, East Stoke, Wareham, Dorset, BH15 2DH, U.K., Russian Institute of Agricultural Radiology and Agroecology, Kievskoe Street, 249020, Obninsk, Russia, and Institute of Terrestrial Ecology, Grange over Sands, Cumbria, LA11 6JU, U.K.