Seasonal and monthly changes of biogenic and oxygen indices in the water of two streams in 2007-10 are discussed in this paper. The streams have similar catchment areas that area managed and used in different ways. The Krzyworzeka stream catchment is covered by rural areas, whereas the Serafa stream flows through built-up and urbanized areas.
Statistical testing using U Mann-Whitney’s nonparametric test was conducted to determine the differences of oxygen and biogenic water quality index values between the growing season and outside the growing season. Statistically significant decreases in ammonium, nitrate, and total nitrogen concentrations, as well as oxygen dissolved in Krzyworzeka Stream, were registered during the growing season. In the Serafa water only the concentrations of dissolved oxygen and biological oxygen demand decreased significantly. On this basis it was established that in clean waters vegetation development considerably influences the content of biogenic compounds. Serious pollution of stream water causes vegetation and the intensity of biochemical processes in water to not cause any clear reduction in biogenic compound concentrations.