Nitrogen and phosphorus compounds in Lake Pluszne

The studies were carried out in Lake Pluszne which is one of the largest (903.3 ha) and deepest (52 m) lakes in the Olsztyriskie Lakeland. The lake can be found approximately 6 kin east of the town of Olsztynek, at 53 degrees 35'9"N and 20 degrees 24'5"E, in the drainage basin of the Marozka - Lyna - Pregola Rivers. Total phosphorus content in the waters of Lake Pluszne ranged from 0.014 mg P/dm(3) to 0.488 mg P/dm(3). Higher concentrations of total phosphorus were noted in the near bottom waters. In the whole study, the dominant form of total phosphorus was organic, which was measured in the range from 0.006 to 0.256 mg P/dm(3). Such phenomenon is typical for eutrophic lakes. Total nitrogen in Lake Pluszne waters oscillated between 0.83 mg N/dm(3) and 3.73 mg N/dm(3). The dominant organic form accounted for 60 to 99% (0.35 mg N/dm(3) to 2.79 mig N/dm(3)) of the total nitrogen. The mineral nitrogen concentrations varied between 0.058 mg N/dm(3) and 0.837 mg N/dm(3) and for most of the year the highest content revealed the nitrate nitrogen(V). The reason for the ongoing eutrophication is the excessive recreation, annual growth of the number of tourists and swimmers, development of the leisure centers on the lake shores as well as of Pluski and Zielonawo villages. The unique landscape and richness of the natural environment in the lake's vicinity are the reasons for its protection that would prevent the water (quality) from further deterioration.