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Hydrological conseąuences of human action..

depths and considerable slope inclinations. Most lakes are overgrown heavily by plants, and numerous depressions filled with peat and gythia at present point to advanced process of lakę disappearance. There are, however, lakes in which a minerał bottom and the scantiness of shore vegetation indicate their physiologically young age. It has not been determined whether this is the effect of conditions unfavourable for eutrophication or of the later formation ofthese lakes. Opinions aboutthe genesis ofthe lakes differ. Some researchers associate their formation with karst processes in Cretaceous bedrock (Wilgat 1954,1963; Wilgat et al. 1991), others with Pleistocene permafrost (Bura-czyński, Wojtanowicz 1974; Wojtanowicz 1993). However, after examining the sediments in several lakes it is known that they were formed not earlier than by the end of Pleistocene about 11,000 years ago (Więckowski, Wojciechowski 1971; Bałaga 1982).

In the environment of the Łęczna—Włodawa Lakę Region water is of great importance. Hydrological features of the terrain — the scantiness of water reserves, the shallow occurrence of groundwaters, the poorly-organized drainage network, the extensiveness of wetlands, the shallowness of lakes and their strong overgrowth — all cause the component to be characterized by exceptionally limited resistance to transformations (Wilgat 1954, 1963; Wilgat et al. 1991; Michalczyk, Bartoszewski et al. 1993; Michalczyk, Dawidek et al. 1993).

FACTORS OF HYDROGRAPHIC CHANGE

It is difficultto estimate the transformation ofthe Lakę Region hydrosphere due to human action, the history of which is long and cannot be reconstructed because of lack of, or inaccurate, documentation. Changes in the hydrosphere are not only caused by direct human interference in it, but also by farming in the environment, which makes it dificult to determine the role of the particular factors of change. Numerous and complicated are the ways of action on the hydrosphere (Wilgat 1979, 1983), and the effects cannot always be associated with the causes. Actions in various directions constitute a factor modifying natural development of the environment. The interlacing of natural and anthropogenic processes can result in unidirectional or antagonistic action on the hydrosphere of variable intensity in the course of time. It is therefore a problematic undertaking to find a point of reference for the determination of the effects of anthropopressure.

The difficulty scalę in studies of anthropopressure is of course differentiated. This is largely determined by features ofthe natural environment, which condition its susceptibility to transformation. When environment resistance to changes becomes smali, anthropopressure is increased and the effects of human action morę evident. However, an attempt at reading direct and indirect effects on the hydrosphere can be morę troublesome.