Seasonal Variability of Physicochemical Parameters of Water Quality on Length of Uszwica River

The Uszwica river catchment is located in the central part of Lesser Poland province, within Brzeski and Bocheński districts. The river is 61.2 km long, and its catchment area is 322.5 km². It is characterized by forest-agricultural land use and high share of residential areas of both compact (the city of Brzesko) and dispersed nature. In the abiotic terms, the Uszwica in its upper course may be classified as a flysch stream (type 12). From the moment of joining the Niedźwiedź, stream until its discharge into the Vistula at km 151+700 it is a sand and clay lowland river (type 19). Hydrochemical research were conducted in the years 2011 and 2012 at two measurement-control points – one located near the mouth of the river (point 1) and one located about 7.5 km downstream from the city of Brzesko (point 2). Each month 18 water quality parameters were determined and they underwent comparative and statistical analyses. Basic descriptive statistics were calculated for both measurement-control points. Then, they were used to determine the ecological potential of the river and to evaluate water quality parameters with respect to its suitability as fish habitat and eutrophication risk. Significance of differences between the values of individual parameters recorded at different measurement-control points was estimated using non-parametric Mann-Whitney U test for α = 0.05. The same test was used to determine the significance of differences between individual parameters for the winter and summer season at each point. Analysis of the results revealed that water flowing via developed areas (point 2) was significantly less saturated with oxygen and contained higher amounts of suspended solids, organic matter and nutrients, as compared to the section of the river flowing mainly through extensively used agricultural areas. Therefore, the ecological potential of the river was considered good in its lower course and poor upstream from point 2. Disturbances in seasonal concentrations of some biogenic factors indicated high degree of water pollution in the middle course of the Uszwica. However, due to intense self-purification, water quality in the lower course was similar to that in natural conditions. On the entire investigated section of the Uszwica does not meet water quality requirements for salmonids and cyprinids, but the habitats are more favorable near the mouth of the river. Waterassessed at point 2 may be classified as eutrophic due to high concentration of total phosphorus.