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Hydrological conseąuences of human action..

In the western part of the Lakę Region such waters occur in 7 lakes (Table 2); they are fewer in the central and eastern part of this region. These are ecosystems with differently-developed efficiency of matter exchange between organie and inorganic components; from mesotrophic (Piaseczno Lakę), through eutrophic (Maśluchowskie, Miejskie, Kleszczów lakes) to dystrophic (Brzeziczno, Łukietek, Czarne Gościnieckie lakes). Because of Iow solute concentration, the waters in the Lakę Region are generally considered to be least-transformed anthropologically (Janiec 1984, 1987). This opinion should be verified.

An analysis of the geochemical medium of the basins of these lakes leads to the conclusion that in their initial stage their waters were simple, of type HCOg-Ca and strongly fresh. Mires were formed as a result of partial transformation of these lakes’ littoral. Energetic transformations in the lake-mire ecosystems conditioned the evolution of their natural waters of the HC0₃—S0₄—Ca type. Then anthropopressure resulted in the formation of tetra- and pentaionic waters (Table 2). Weighted means of macrocomponents in 7 studied lakes ąualify the thus-formed water as pentaionic of the type S0₄-HC0₃-Cl-Ca-Na (in the Shtchukariev-Priklonskiy classification). Multi-ionic waters of such a type do not occur as natural in the phreatic zonę. Then from the natural point of view they are waters strongly transformed anthropogenetically. The percentage of carbonate hardness in the total hardness (on average about 62%) and a high value of the Mg/Ca coefficient (0.338) also account for advanced anthropogenization of the water of the 7 lakes studied.

Thus the measure of anthropogenic transformation of waters need not be their inereased solute concentration nor the decrease of the so-called water ąuality class. However, a change in the hydrochemical type of water always indicates human action. Waters of other lakes of a solute load over 150-200 mg/1 are morę resistant to changes and are ąualified as diionic or triionic types (HC0₃-Ca, HC0₃-S0₄-Ca). Such lakes include: Zagłębocze, Rotcze, Sumin, Białe Włodawskie. Accordingly, the conclusion is that hyperfresh waters of the 7 lakes studied are among those most changed and are not the "purest" in the Region.

In the middle part of the Lakę Region, on elevations built of marły limestones of the Upper Cretaceous, the ąuality of waters is different, and their solute load several times higher. These are simple waters, bicarbonate-calcium (HC0₃—Ca), less liable to anthropogenetic transformations.

In the eastern part of the Lakę Region, the lakę waters are of similar solute load to those in the western part (70—150 mg/1) and are eąually sensitive to pollution.

In the ion composition of most lakes the Ca-HC0₃ ion pair predominates. This gives evidence of the significance of carbonates in the Chemical composition of water even in an environment characterized by a deficiency of carbonate minerals. Calcium and magnesium contents in the waters of