1. Dept of Ecology and Genetics; Univ. of Oulu; PO BOX 3000 FI-90014 University of Oulu Finland
2. School of Science and Technology; Nottingham Trent Univ.; Nottingham UK
3. Finnish Environment Institute, Freshwater Centre; Oulu Finland
4. Water Resources and Environmental Engineering Research Unit; University of Oulu; Finland
5. Oulanka Research Station; Kuusamo Finland
6. Finnish Environment Institute (SYKE); Freshwater Centre; Helsinki Finland
7. Finnish Environment Inst.; Freshwater Centre; Oulu Finland