## 3 Results
### Water Chemistry  
The cutoff sewage inflow to studied lakes caused highly significant variation in the total phosphorus (TP) only in the bottom water layers of the Karczemne Lake and the entire water volume of the Klasztorne Male Lake (Table 3). In 2017, the mean TP concentration in the surface water layer of Mielenko Lake was 0.189 mg P L\({}^{-1}\) (\(\pm\)0.079) and 0.277 mg P L\({}^{-1}\) (\(\pm\)0.122) in the near-bottom layer (Figure 5, Table 4). In 2019, after protective treatments were implemented, the average TP concentration of the entire volume of water was 0.185 mg P L\({}^{-1}\) (\(\pm\)0.059). In 2017, the mean TP concentration in the surface water layer of Karczemne Lake was 0.853 mg P L\({}^{-1}\) (\(\pm\)0.120, and 2.899 mg P L\({}^{-1}\) (\(\pm\)2.522) in the near-bottom layer. In 2019, after modernization of the city's sewage system, the average TP concentration in the surface water layer of Karczemne was 0.746 mg P L\({}^{-1}\) (\(\pm\)0.298), and the near-bottom TP concentration was 0.771 mg P L\({}^{-1}\) (\(\pm\)0.303) (Figure 5, Table 4). In Klasztorne Male Lake, in 2017, the mean TP concentration in the surface water layer was 0.434 mg P L\({}^{-1}\) (\(\pm\)0.179), and was 11.976 mg P L\({}^{-1}\) (\(\pm\)4.598) at the lake bottom (Figure 5, Table 4). In 2019, in the merrocitic Klasztorne Male Lake, the mean TP concentration in the surface water layer was 0.232 mg P L\({}^{-1}\) (\(\pm\)0.044) and 4.907 mg P L\({}^{-1}\) (\(\pm\)4.611) in the bottom layer (Table 4). In 2017, in the case of Klasztorne Duze Lake, the mean content of TP in the surface water layer was 0.275 mg P L\({}^{-1}\) (\(\pm\)0.118), and in the near-bottom water, it was 1.024 mg P L\({}^{-1}\) (\(\pm\)0.566). In 2019, after protective techniques were implemented, the mean concentration of TP was 0.219 mg P L\({}^{-1}\) (\(\pm\)0.066) in the surface water of Klasztorne Duze Lake, while that at the bottom was 1.396 mg P L\({}^{-1}\) (\(\pm\)1.367) (Figure 5, Table 4). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & \multicolumn{2}{c}{**Mielenko**} & \multicolumn{2}{c}{**Karczemne**} & \multicolumn{2}{c}{**[PERSON]**} & \multicolumn{2}{c}{**Klasstorme Duze**} \\ \cline{2-10}  & & & & & & & & & \\ \cline{2-10}  & Min/Max & SD & Min/Max & SD & Min/Max & SD & Min/Max & SD \\ \hline TP & surface & 0.119/0.368 & 0.079 & 0.631/0.950 & 0.120 & 0.251/0.780 & 0.179 & 0.134/0.446 & 0.118 \\ \([\text{mg L}^{-1}]\) & bottom & 0.147/0.490 & 0.122 & 0.667/0.740 & 0.252 & 0.760/0.260 & 4.59 & 0.295/1.930 & 0.566 \\ TN & surface & 1.47/3.01 & 0.541 & 1.32/5.570 & 1.320 & 1.83/2.40 & 0.182 & 1.25/2.12 & 0.273 \\ \([\text{mg L}^{-1}]\) & bottom & 1.43/3.00 & 0.531 & 1.33/4.71 & 1.008 & 17.24/22.38 & 2.306 & 1.87/6.34 & 1.565 \\ Chlorophyll i al [ug L\({}^{-1}]\) & 8.44/3.83 & 1.388 & 26.16/1.251 & 3.260 & 28.66/6.45 & 12.65 & 15.67/0.71 & 1.681 \\ SD Visibility [m] & 0.4/0.8 & 0.138 & 0.2/0.5 & 0.112 & 0.3/1.1 & 0.267 & 0.4/1.8 & 0.467 \\ \hline  & & & & & & & & \\ \hline  & & & & & & & & & \\ \hline  & & & & & & & & & \\ \hline  & & & & & & & & & \\ \end{tabular}
\end{table} 
Table 4: Variability of nutrients, chlorophyll i and Secchi disc visibility in study lakes. Figure 5: Mean annual values of total phosphorus (TP) in the water of Kartuzy lake complex in selected research years (box \(\pm\) SEM, whisker plots \(\pm\) Standard Deviation). The cutoff of the sewage inflow to the lakes caused highly significant variability in the total nitrogen (TN) values only in the bottom water layers of Klasztorne Male Lake (Table 3). In the surface water layer of Mielenko Lake, in 2017, the average concentration of TN was 2.086 mg N 1\({}^{-1}\) (\(\pm\)0.185), and in the near-bottom water, it was 2.200 mg N 1\({}^{-1}\) (\(\pm\)0.531) (Figure 6, Table 4). In 2019, after protective treatments were implemented, in the entire water volume of Mielenko Lake, the mean concentration of TN was 2.986 mg N 1\({}^{-1}\) (\(\pm\)1.297).