INFLUENCE OF LOW RETENTION RESERVOIR ON WATER QUALITY OF SUPRASL RIVER

Present research was aimed at evaluating the water quality in small retention reservoir localized within the agricultural catchment in Wasilkow. Three measurement points were selected during the study; their spatial distribution resulted from a possibility to record changes in physicochemical properties of water occurring in analyzed reservoir. Point No. 1 was localized near the inflow, No. 2 in the middle part, No. 3 at the water outflow of the reservoir. Physicochemical analyses of water included following determinations: apparent and real color, turbidity, oxidizability, (specific electrolytic) conductivity, acidity, Kjeldahl's organic nitrogen, ammonia, nitrates(III), nitrates(V), phosphates, total iron, and manganese. Analyses of water samples collected from the surface layer of the littoral were carried out once a month since May 2008 till March 2009. Determinations of water physicochemical parameters were made in accordance with obligatory methods and statistical processing of all achieved data was performed applying two-factorial variance analysis for particular dates and sampling points. Differences were verified using Tukey test. A prominent seasonality of all examined parameters was observed when analyzing achieved results. Two-factorial variance analysis of mean values of apparent and real color, turbidity, oxidizability, (electrolytic) conductivity, acidity, phosphates, and manganese revealed significant differences between sampling dates, while sampling points had no considerable importance. The Tukey test also verified that significant differences between sampling dates and points were present in the case of nitrates(V), while for nitrates(III) no factor was significant. Only in the case of iron the sampling point appeared to be the most significant, whereas sampling dates were insignificant. Waters supplying Wasilkow reservoir had more often much lower values of examined physicochemical parameters than those flowing into it, hence the quality of river water below the reservoir became much worse. Observations upon a spatial distribution of studied indicators revealed that reservoir in Wasilkow had no abilities to self-purification.