1. Department of Limnology, University of Gdańsk, Bażyńskiego 4, 80-952 Gdańsk, Poland1
2. Department of Lakelands Geography, University of Gdańsk, Bażyńskiego 4, 80-952 Gdańsk, Poland2
3. Department of Hydrology and Water Management, Nicolaus Copernicus University, Gagarina 9, 87-100 Toruń, Poland3