2949775613

143

Hydrological conseąuences of human action..

all lakes is on average 1.43 and 0.47 meq/l, with extreme values 0.18-3.48 meq Ca/1 and 0.18-0.9 meq Mg/l, respectively. The big differentiation in calcium and magnesium contents may result from geochemical variability of the environment and anthropogenetic influences, among other things, foreign water transfers. The Mg/Ca coefficient, exceeding an average of 0.33, is in natural conditions characteristic for waters in contact with dolomite limestones or carbonate loesses.

The functioning of lakę ecosystems is influenced significantly by the content of biotic components in water, largely phosphorus and nitrogen compounds, and the oxygen indices connected with them. They determine to a considerable extent the eutrophication intensity. Studies of P0₄, N_x and 0₂ content were carried out selectively in the Łęczna-Włodawa lakes (Cydzik, Soszka 1988). Phosphorus is considered an eutrophication index, although its amount in waters depends also on the development intensity of macrophytes in the body of water and the total primary production. In lakes thermally stratified it occurred from tracę amounts to 0.12 mg P0₄/1 (total phosphorus) in the epilimnion to 1.25 mg P0₄/1 in the ground hypolimnion; whereas in polymictic lakes it reaches 0.16 mg P0₄/1. In lakę waters various nitrogen forms were studied (NH₄, N0₃, N and N_total); they occur at amounts from 0.01 mg/l to 3.0 mg/l, but organie nitrogen predominates.

One of the main factors changing the hydrosphere quality in the Lakę Region is the Wieprz—Krzna canal leading fertile carbonate waters from the upper Wieprz river basin. The inflow of these waters into some lakes (among others: Łukie, Zaglębocze and Uscimowskie) has caused alkalization and changes of water-mire ecosystems. The scalę of these transformations cannot be determined because of a lack of studies in the period preceding strong human interference. Particularly big changes took place in lakes tumed into retention reservoirs filled every year with allochthonous waters and successively emptied.

To datę the influence of the Wieprz-Krzna canal has caused: a) considerable changes in water quality in the lakes included into the systems of artificial distribution of foreign waters, b) accelerated eutrophication, e.g. in Krzczeń, Krasne, Białe, Sosnowickie and Bialskie lakes, c) a distinct retreat of advanced dystrophication in Czarne Sosnowickie Lakę, d) the initiation of dystroph-ization in lakes strongly eutrophicated (Bikcze Lakę) as a result of radical hydrological changes.

CONCLUSIONS

Man’s influence on the hydrosphere is a process occurring stepwise, particularly in cases of big water investments, and at the same time of a continuous character. In generał it is inereasing with the inereasing population and developing technology. In the long history of this influence periods can be distinguished which differ in the character and intensity of anthropopressure. In the case of the Lęczna-Wlodawa Lakę Region three periods can be