179 Over 200 years of drainage practices and lake level drawdown in the Uścimowskie Lowering ... Limnological Review (2012) 12, 4: 179-190 DOI 10.2478/v10194-012-0058-0 Introduction Water represents a constitutive element shap- ing the ecosystems of the Łęczna-Włodawa Lakeland. Within the last centuries, it has been subject to sys- tematic, continuously increasing anthropopressure (Chmielewski and Radwan 1993). One of its symp- toms is the development of drainage systems, leading to the incorporation of lakes in the drainage network (Wilgat 1991). As a result of those two processes, the character of lakes changes from closed- to open-drain- age, and a decrease in the water level and reduction of maximum stages occur. Although natural processes also lead to the development of a drainage network, the human melioration practices substantially acceler- ate the process. Moreover, a change in the character of a lake from closed- to open-drainage or fow-through by its incorporation in the drainage system results in a number of not only hydrological, but consequently also hydrobiological changes. In the Łęczna-Włodawa Lakeland, melioration activities were conducted with particular intensity, Over 200 years of drainage practices and lake level drawdown in the Uściwierskie Lowering (Łęczna-Włodawa Lakeland) Grzegorz Kowalewski Department of Biogeography and Palaeoecology, Adam Mickiewicz University, Dzięgielowa 27, 61-680 Poznań, Poland, e-mail: ichtys@amu.edu.pl Abstract: Meliorations of the Łęczna-Włodawa Lakeland have considerably determined its water relations within the last more than 200 years. Te analysis of the map by Anton Mayer von Heldensfeld, so far not applied in studies on the drainage network of this lakeland, executed in the years 1801-04, revealed the drainage of the Uściwierskie Lowering already at the turn of the 18 th and 19 th century. Tis shifs the commencement of strong anthropogenic impact on this area to a considerably earlier period than was previously assumed. Te lakes subject to analysis (Rotcze, Uściwierz, Bikcze, and Lakes Piaseczno and Łukie neighbouring with the Lowering) were incorporated into the drainage system in various periods. Such incorporation of a water body involved water level drawdown. Te water level decreased frst in Lake Bikcze, and the latest in Lake Rotcze. More detailed information on changes in the water level in the lakes of the Uściwierskie Lowering since 1882 was obtained based on calculation and on comparison with current data of measurements conducted by Rostworowski. Te analysis revealed that the water level in Lakes Bikcze and Piaseczno, although fuctuating, has not changed within the last 130 years, whereas the water level in Lake Uściwierz decreased by 33 cm, and in Lake Rotcze by 90 cm. Key words: Łęczna-Włodawa Lakeland, Uściwierskie Lowering, artifcial drainage, drainage network, water level fuctuations, Heldensfeld’s map because afer the 2 nd World War, access to many set- tlements in the melting season was still very difcult. Te most intensive works were conducted since 1954, in connection with the construction of the Wieprz- Krzna Canal, completed in 1961 (Wilgat et al. 1991, Michalczyk 1994b). According to Rostworowski (1882, p. 77), melioration of the Łęczna-Włodawa Lakeland was “an issue already existing for a long time in the form of a project of a canal from the Wieprz to the Bug River” [“kwestyją istniejącą od dawna w formie projektu kanału od Wieprza do Bugu”]. Meliorations resulted in increased runof of surface waters and a decrease in the level of groundwaters, as well as trans- formation of peatlands into muck (Michalczyk 2009). In the years 1952-92, 5 out of 68 lakes existing in the lakeland disappeared completely (Chmielewski and Chmielewski 2010). Due to this, literature relatively frequently un- dertakes the issue of anthropogenic changes in water relations. Meliorations in the Łęczna-Włodawa Lake- land are reconstructed based on historical maps and aerial photographs. Whereas changes in the drainage