The average values of TP, SD, Chl a, TN and TN:TP measured in the surface

waters in summer ( Kajak 1983, Zdanowski 1983) were also APO866 research buy used in the assessment of the Vistula Lagoon’s trophic state. Vollenweider’s method for assessing a water body’s trophic state (1989), accepted by the Organization for Economic Co-Operation and Development (OECD) and based on the average values of selected parameters measured in spring and summer, was also applied. Samples for the microscopic determination of phytoplankton were fixed with Lugol’s solution. Phytoplankton was analysed under an inverted microscope (Nikon TMS, Tokyo, Japan) with 200×, 400× and 600× magnification. The counting units (N) were cells, coenobia or trichomes 100 μm in length. To calculate the biomass, the species were approximated to simple geometric or combined forms. Counting and biomass determination were performed in accordance with the recommendations of the Baltic Monitoring Programme ( HELCOM). The average concentration of total phosphorus (TP) during buy Everolimus the whole measurement period was 160.32 ± 61.18 μg P dm−3; in summer it exceeded 180 μg P dm−3. The phosphorus content in the water was the highest in 2009 (av. 169 μg P dm−3). The concentration of chlorophyll a was extremely variable, the highest value being noted in 2008 (54 μg dm−3).

The total nitrogen content of Vistula Lagoon waters was stable in 2008–2009 at an average level of 1.36 mg N dm−3; the average level in 2007 was lower – 0.86 mg N dm−3. During the study period the average salinity was most ∼ 3.7 PSU, the water transparency low, the oxygen content high and the mean water temperature 18°C. The average value of the TN:TP ratio was < 10, but the maximum value was slightly in excess of 20 in June 2008 ( Table 1). The trophic state indices calculated for the

summer months of 2007–2009 for the surface waters were: TSI (Chl a) 53–90, TSI (TP) 71–89, TSI (TN) 41–65 and TSI (SD) 65–83. These values are high, indicating that the Vistula Lagoon is at least eutrophic. The combined trophic index was the highest in 2009. The average value of TSI (TP) was 80, and even exceeded 82 in July. The mean value of TSI (Chl a) was also high (78) and in July it was 83. The same tendency was observed in the case of TSI (SD), its highest value being noted in June (83). The trophic states of the Vistula Lagoon waters were determined on the basis of the four classification systems described above and are presented in Table 2. The values of TSI were calculated based on the formulas given below the table. Analysis of the phytoplankton revealed a significant contribution of planktonic blue-green algae, especially colonial species with picoalgal and larger cell sizes belonging to the Chroococcales, Oscillatoriales and the typical bloom-forming Nostocales.