Changes of water quality of the transboundary Wisznia river in the years 1990–2012

W pracy przedstawiono ocenę jakości wód powierzchniowych transgranicznej rzeki Wisznia (dorzecze górnej Wisły). Analizie poddano 8 wskaźników jakości wody, takich jak: azot całkowity, azot amonowy, azot azotanowy, fosfor, siarczany, chlorki, wapń, biologiczne zapotrzebowanie na tlen (BZT5). Do analizy wykorzystano dane z lat 1990–2012, dotyczące jakości wody w 2 punktach pomiarowokontrolnych. Otrzymane wyniki były zróżnicowane, jednak ogólnie zaobserwowano zmniejszenie poziomu zanieczyszczeń. Odnosi się to do wszystkich analizowanych wskaźników. Jest to spowodowane przemianami w rolnictwie oraz budową oczyszczalni ścieków komunalnych.This paper presents the water quality changes of the transboundary Wisznia River (Poland). The environmental state of this transboundary river is described in terms of monthly data for the main physicochemical and biological parameters. The eight indicators of water quality taken into account were: ammonium nitrogen (NH4+), nitrate nitrogen (NO3-), total nitrogen (N), total phosphorus (P), sulphates (SO42-), chloride (Cl-), calcium (Ca) and biological oxygen demand (BOD). And biological Oxygen Demand (BOD) is one of the most common measures of pollutant of organic material in water, and is used in environmental monitoring. The distribution frequency of the above water quality indicators in Wisznia River were established for the study period of 1990–2012. The nutrient concentrations (NH4+, N, P) were clearly low and never exceeded the boundary level of the first (1) and second (2) class purity. This pertained to all the analysed components, however, the negative changes were found for the 5 day biological oxygen demand. This can be the result of decreasing anthropopressure in the area because the main feature of the studied area is agricultural and forest land cover with a low population density. The analysis proved that the indicators which lowered the water quality the most were: BOD5, chlorides and calcium had a smaller impact on the classification of water cleanness. This shows that surface water has been affected in quality by anthropogenic influence. An analysis of salinity indicators indicates a clear improvement of water cleanness which happened in the recent years