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H. Maruszczak, M. Wilgat

Indices of the solute concentrations of river waters were calculated as mean values from the measurement series we had for the years 1976-1985. Data of that decade did not concem the whole Vistula river basin, because work on the map was started in 1981. We began in the south—east part of the basin and the work was continued successively in the following years. So, for the mentioned part of the basin we used data from the years 1976—1980.

Discharges of river waters were estimated according to the map worked out for Poland’s area by J. Stachy (1966). It shows the mean values of many years calculated from empirical formulae, which define the dependence of discharges on climatic conditions. These formulae allow us to calculate discharges at each point for which the reąuired meteorological data are known. We could also use a morę recent map (Stachy et al. 1977) on which isolines were plotted on the basis of the actual discharge measurements from the years 1951—1970. However, points of discharge measurements are considerably fewer than meteorological offices. Thus, isolines plotted from discharge measurements give a morę generalized picture. This fact induced us to use the map from an earlier paper.

It seems that the level of precision of the presented method of solute yield calculations is sufficient for the determination of a balance. This can be proved by the results of calculations of the solute yield from twenty selected catchments in the Vistula river basin (see Table 1). These calculations were madę not only in the way presented (by multiplication of mean indices of ten years), but also by adding monthly values of the solute yield. In the case of weakly industrialized catchments the results obtained the first way — used in the preparation of our map for rural areas — differ by not morę than several percent from the results obtained the second way — morę precise but reąuiring morę measurement data and relatively large amounts of time for calculations. Thus, the errors resulting from the usage of a morę simple way of calculating river solute yield are rather smali. Probably they are smaller than analytic errors of measurements of solute concentrations by evaporation — the method used in the Provincial Centres for Studies of the Environment and its Control.

Analysis of our map shows that the indices of river solute yield from the rural areas depend mainly on discharges of river waters. The influence of the geological structure and relief is most elear when variously leachable rocks occur in particular hydrological regions. For example, in the calcareous Western Tatra Mts we have indices over 150 tkm^-2y^-i, and in the granitic Eastern Tatra Mts even below 20 tkm^-2y^-1.

The discussed map presents indices of discharge of solutes coming from: 1) largely natural, Chemical denudation of the lithosphere in the major part of the basin; 2) precipitation, which at present is already rather strongly polluted with different anthropogenic substances; 3) agricultural chemization, i.e. mainly fertilizers and different substances used in crop production; 4) farm sewage. This map constitutes a background against which we can present the sources of Chemical pollution of river waters with municipal and industrial wastewater.