The effect of catchment on water quality and eutrophication risk of five shallow lakes (Polesie Region, Eastern Poland)

The nutrient loads from the terrestrial catchments, (based on the distribution of soils and their use) were estimated, compared with that deriving from the atmosphere, and analysed from the view point of the present lake water quality (pH, transparency, electrical conductivity, total suspended solids, concentrations of TN, TP, Ca, Mg, K and Na). Five shallow (mean depth 0.9-3.4 m) and small (area < 100 ha) lakes were selected in Leczna-Wlodawa Lakeland, a part of Polesie region (Eastern Poland). The contribution of the atmospheric deposition of N and P to the total loads (both from air and the land) varied greatly between the lakes (2-48% and 1-40%, respectively) while that of other elements did not exceed 16%. The lake catchments differed substantially in the percentage of soil types and their use. The most fertile soils were used as arable fields and the least fertile were afforested. The load of N and P in g m(-2) of a lake surface per year ranged from 2.1 to 55.5 and 0.05-1.33, respectively. Average (May-October) concentrations of TN and TP in the lake waters varied from 0.92 to 1.70 mg dm(-3) and 27.1-238.9 mu g dm(-3), respectively. There was a strong linear correlation between the percentage of particular soil types, nutrient inputs to the lakes and their concentrations in the lake waters, especially for the TN and TP. In addition, the physical and chemical properties of lake water depended significantly upon ratio between lake surface and cachtment area, as well as on lake morphometry. The eutrophication hazard of the lakes, evaluated according to Vollenweider's criteria, was the highest for the lakes where the forests and grasslands occurred in the smallest proportions in the catchments, and the contribution of the fertile, cultivated soils was the highest.