## 4 Results
Part of a species was found in one sector in one study year (2018): PFR (_Calla plaplstris_, _Carex pseudocyperus_, _Carex vesicaria_, _Iris pseudacorus_ and _Equisetum fluviatile_); R (_Galium palustre_); and FR (_Fontinalis antypyrevtica_) (Table 8). The calculated Jaccard's species similarity coefficient for the analysed littoral phytocoenoses in sectors of Lake Piaseczno in 2007 varied from 0.36 (PFR-RA) to 0.63 (RA-FR) and in 2018 from 0.26 (PFR-FR) to 0.64 (RA-FR), suggesting diversity of flora within the study sectors. In the case of the mutual comparison of the species composition of flora of the lake's littoral in 2007 and 2018, the Jaccard's coefficient values were in a range from 0.53 (RA-RA) to 0.88 (FR-FR), suggesting more considerable transformations in the species composition of plants (Table 9). The distribution and biomass of macrophytes occurring in the phytolittoral of Lake Piaseczno were evidently variable in particular study sectors. The highest species diversity occurred in sector PFR, particularly among emerging macrophytes. They reached the greatest range (1.4 m of depth), density (52 ind\(\cdot\)m\({}^{-2}\)) and biomass values here (Table 10). The lowest values of the analysed properties of macrophytes occurred in sector RA, with the exception of the biomass of submerged macrophytes, which varied from 216.9 g\(\cdot\)m\({}^{-2}\) to 270.9 g\(\cdot\)m\({}^{-2}\) in the sector. The general pattern observed in all of the analysed sectors involved high values of one group of macrophytes, and lower values of the other. If emerging macrophytes reached higher biomass values, submerged macrophytes automatically showed a lower value. A well-developed reed belt may limit the supply of biogenic substances to the depths of the lake and, therefore, the development of the occurring macrophytes. The width of the reed belt is, on the one hand, determined by the morphometric parameters of the lake, and, on the other hand, by the amount of supplied biogenic substances from the buffer zone. The widest reed belt--of more than 100 m--occurred in sector PFR and was approximately 40 m in sector R. The biomass of this group of macrophytes was high (Table 10). Therefore, a higher than average external supply of biogas presumably occurs here from this form of land use in the zone. The productivity of the littoral of Lake Piaseczno in the 2015 and 2018 summer seasons, measured with values of biological indicators of water troply, suggested the intensification of its eutrophication in different ways. This could be related to the diverse dynamics of the internal metabolism of the lake, and--in the modifying effect on biogeochemical buffer zones of the shores and littoral of the lake--variable amounts and rates of supply of biogenic substances from the catchment. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **2007** & & & **2018** & \\ \hline
**PFR–R** & **R–RA** & **RA–FR** & **PFR–R** & **R–RA** & **RA–FR** \\
0.38 & 0.58 & 0.63 & 0.33 & 0.62 & 0.64 \\
**PFR–RA** & **R–FR** & & **PFR–RA** & **R–FR** & \\
0.36 & 0.38 & & 0.3 & 0.45 & \\
**PFR–FR** & & & **PFR–FR** & & \\
0.38 & & & 0.26 & & \\ \hline \hline \multicolumn{6}{c}{**2007–2018**} \\ \hline
**PFR–PFR** & **R–R** & **RA–RA** & **FR–FR** & & \\ \hline
0.6 & 0.6 & 0.53 & 0.88 & \\ \hline \hline \end{tabular}
\end{table} 
Table 9: The Jaccard’s species similarity coefficient values for macrophytes for sectors of the littoral of Lake Piaseczno in 2007 and 2018 (extreme values are marked with colours: yellow, min; orange, max). Gross primary production of phytoplankton (GPP) in the 2015 summer season adopted a range of average values from 11.05 (FR) to 30.28 (PFR) mg \(\mathrm{C_{ass}\cdot m^{-2}\cdot h^{-1}}\) (132.6-363.4 mg \(\mathrm{C_{ass}\cdot m^{-2}\cdot d^{-1}}\)), and in 2018 from 11.88 (FR) to 31.15 (R-RA) mg \(\mathrm{C_{ass}\cdot m^{-2}\cdot h^{-1}}\) (142.6-373.8 mg \(\mathrm{C_{ass}\cdot m^{-2}\cdot d^{-1}}\)) (Figure 6).