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H. Maruszczak, M. Wilgat

(Chojnacki 1967) and its later tendency to increase were taken into consideration. As the solute concentration was still increasing in the early 80’s we assume that in the years 1976-1985 the mean value of the discussed component was 9 t km^_2y^_1. In particular catchments of the Vistula river basin this value varied in linę with the degree of atmospheric pollution. As the measure of this pollution we took the ąuantity of atmospheric S0₂ "flux" on Poland’s territory, shown by isolines after J. Juda et al. (see Więckowski 1989, p. 35). Thus, estimated ąuantities of the solutes coming from precipitation vary in the examined catchments in the rangę 4-23 t km^-2y"¹ (Table 2).

Component coming from agricultural chemization. This percentage was calculated identically as in the previous paper. Thus, we took into consideration the results of investigations of fertilizer losses (Wilamski and Śliwa 1978, Pondel and Terelak 1981, Pondel et al. 1978) due to leaching caused by rain-water. In this way it was estimated that the losses of NPK fertilizers amounted to 10-15%, and those of calcic fertilizers to about 50%. The total losses were calculated using statistical data for 1980, which illustrate the supply of fertilizers in the gminas within particular catchments. This varied in the rangę 3.2-10.0 t km^_2y^_1 (Table 2). Thus, the percentage of this component is considerably lower than of that coming from precipitation.

Component coming from farm sewage. In the previous paper this was not taken into consideration because of a lack of suitable data. It was assumed that the percentage of this component was very Iow due to the weak infrastructure of rural settlements. However, we took into consideration this component in this paper, noticing particularly its differentiation in the examined catchments. We assumed arbitrarily that the mean index for the percentage of such sewage for the whole Vistula river basin was 1.0 t km'²^¹, i.e. many times lower than in the case of the component coming from agricultural chemization. Differentiation of this index in particular catchments was calculated in regard to the population density of rural areas and the cultivation level, the measure of which was the ąuantity of used fertilizers. Thus the estimated index varied in the rangę 0.5-2.31 km~²y^_1 in the catchments examined (Table 2).

THE STRUCTURE OF THE RIVER SOLUTE YIELD IN THE EXAMINED CATCHMENTS

The calculated values of the particular components of the solute yield are presented in Table 2, and Fig. 3. Despite very different areas of the examined catchments (from 1400 to 39,100 km²) we were able to define the regional differentiation of the solute yield structure.

The greatest differences are between strongly-industrialized and rural areas. The Little Yistula river catchment (wastewater constitutes here almost