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Structure of the solute yield in the Vistula..

determination on our map (using a planimeter) of the ranges of the particular solute yield indices from rural areas; on this basis the mean indices of the solute yield from the analyzed catchments were calculated as "weighted mean". The differences between the indices of the total solute yield and those from rural areas can be considered as a quantitative measure of the solutes coming from municipal and industrial wastewater. In the case of little-polluted areas these differences are smali, so in this way we probably obtain results with a big error (for example for the catchments of the Sola, Raba and Wieprz rivers). We have no adeąuate principles to determine this error.

Before making the finał balance calculations of the percentages of municipal and industrial wastewater we should consider the represen-tativeness of the measurement data from the years 1976-1985. The successive years of this period were characterized by a great variation in river discharges and thereby of the solute yield. In the discussed decade, in many catchments the mean discharges were higher than the average for the period 1951-1975 (or 1951-1970); a higher increase, about 46%, occurred in the Wkra river catchment. However, in two cases they were lower than the average ones for many years, namely, in the Sola river catchment even by about 31.5%, and in the Nida river catchment by about 7.5%. In seven cases the differences in relation to average values for many years did not exceed 5%.

In the calculations madę while preparing the map of the solute yield from rural areas, we took the values of discharges determined empirically on the basis of meteorological measurement series from many years. Therefore, we decided to reduce — i.e. respectively decrease or increase — the ten-year—mean (1976-1985) discharges to mean values for many years. Accordingly, the indices of solute yield were also reduced for calculation of the balance. The percentage of municipal and industrial wastewater in total solute yield calculated in this way is presented in Table 2. This shows that the percentage varies from about 2 to 90%. The highest is of course in the catchments polluted by wastewater from the Upper Silesian Coal Basin (the Little Vistula and Przemsza rivers), while the lowest is in the Dunajec river catchment which is characterized by the highest index of natural Chemical denudation.

BASIC DATA FOR ESTIMATION OF THE PERCENTAGE OF OTHER COMPONENTS OF SOLUTE YIELD

Now we can present the problem of component ratios of that part of the total solute yield which comes from rural areas and is shown on our map

(Fig. 1).

Component coming from precipitation. In the previous paper (Maruszczak 1990), the percentage of this component in the solute yield from the Vistula river basin was estimated at 8 t km^-2y^-1, amounting to 16%. The results of measurements of the solute concentration in precipitation in the 60’s