1. Department of Hydrology and Limnological Research Station, University of Bayreuth, 95440 Bayreuth, Germany, Kuopio Unit, Geological Survey of Finland, Post Office Box 1237 (Neulaniementie 5), 70211 Kuopio, Finland, and Department of Geography and Centre for Climate & Global Change Research, McGill University, 805 Sherbrooke Street West, Montreal H3A 2K6, Canada