## 3 Results  
### External Load of Nutrients  
The inflow of nutrients to Mielenko Lake from the catchment areas and the atmosphere in 2017 took place via several routes of which the following were of basic importance: areal sources, including direct catchment (3 kg P y\({}^{-1}\), 72 kg N y\({}^{-1}\)) and water inflow via watercourse flow through forested areas that reached the northeastern part of the lake (1.8 kg P y\({}^{-1}\), 13 kg N y\({}^{-1}\)); point sources, including rain sewage collected with a separator (2.5 kg P y\({}^{-1}\), 34 kg N y\({}^{-1}\)) and atmospheric sources (7.5 kg P y\({}^{-1}\), 30 kg N y\({}^{-1}\)); and recreational sources, including angling biogenic salts introduced with baits (2.7 kg P y\({}^{-1}\), 55.2 kg N y\({}^{-1}\)) (Figures 3 and 4). The total annual load of phosphorus (P) introduced to the lake was 17.5 kg P y\({}^{-1}\) (per lake area 0.220 g P m\({}^{2}\) y\({}^{-1}\)), whereas that of nitrogen (N) was 204.2 kg N y\({}^{-1}\) (per lake area 2.600 g N m\({}^{2}\) y\({}^{-1}\)). Figure 3: Annual load of phosphorus (P) (kg P y\({}^{-1}\)) entering to Kartuzy lake complex. After modernization of the city's sewage system, the annual load of nutrients introduced to Mielenko Lake by direct catchment (3 kg P y\({}^{-1}\), 72 kg N y\({}^{-1}\)), point sources (\(<\)0.1 kg P y\({}^{-1}\), 0.1 kg N y\({}^{-1}\)), atmospheric sources (7.5 kg P y\({}^{-1}\), 30 kg N y\({}^{-1}\)), and recreation-angling biogenic salts introduced with baits (1.4 kg P y\({}^{-1}\), 23.0 kg N y\({}^{-1}\)) was lowered (Figures 3 and 4). The total annual load of nutrients introduced to the lake in 2019 was 11.9 kg P y\({}^{-1}\) (per lake area 0.15 g P m\({}^{2}\) y\({}^{-1}\)) for phosphorous and 125.1 kg N y\({}^{-1}\) (per lake area 1.6 g N m\({}^{2}\) y\({}^{-1}\)) for nitrogen. In the case of Karczemme Lake, the inflow of biogenic salts to the lake from the catchment and atmosphere in 2017 involved the following basic components: areal sources (4.5 kg P y\({}^{-1}\), 108.4 kg P y\({}^{-1}\)), such as the tributary of the Klasztorna Struga river(56.4 kg P y\({}^{-1}\), 417.5 kg N y\({}^{-1}\)); point sources, including six rain sewage collectors, two with illegal inflow of raw wastewater (69.8 kg P y\({}^{-1}\), 492.3 kg N y\({}^{-1}\)); atmospheric sources (19.5 kg P y\({}^{-1}\), 75.2 kg N y\({}^{-1}\)); and recreational sources, such as angling (14.1 kg P y\({}^{-1}\), 286 kg N y\({}^{-1}\)) (Figures 3 and 4). The total loads of (phosphorus) P and nitrogen (N) introduced to Karczemme Lake in 2017 were 164.3 kg P y\({}^{-1}\) (per lake area 0.407 g P m\({}^{2}\) y\({}^{-1}\)) and 1379.4 kg N y\({}^{-1}\) (per lake area 3.41 g N m\({}^{2}\) y\({}^{-1}\)), respectively. In 2019, after modernization of the sewage system in Karturz, the annual load of nutrients was lower: areal sources (4.5 kg P y\({}^{-1}\), 108.4 kg P y\({}^{-1}\)), such as the tributary of the Klasztorna Struga (56.3 kg P y\({}^{-1}\), 521.6 kg N y\({}^{-1}\)), point sources, such as that of a rain sewage collectors, two with illegal inflows of raw wastewater (17.2 kg P y\({}^{-1}\), 94.1 kg N y\({}^{-1}\)), atmospheric sources (19.5 kg P y\({}^{-1}\), 75.2 kg N y\({}^{-1}\)), and recreational sources, such as angling (7 kg P y\({}^{-1}\), 142 kg N y\({}^{-1}\)) (Figures 3 and 4). The total loads of (phosphorus) P and nitrogen (N) introduced to Karczemme Lake in 2019 were 104.5 kg P y\({}^{-1}\) (per lake area 0.258 g P m\({}^{2}\) y\({}^{-1}\)) and 941.3 kg N y\({}^{-1}\) (per lake area 2.329 g N m\({}^{2}\) y\({}^{-1}\)), respectively. Klasztorne Male Lake in 2017 was supplied from a direct catchment (1.3 kg P y\({}^{-1}\), 26 kg N y\({}^{-1}\)), a surface inflow source (Klasztorna Struga) (358 kg P y\({}^{-1}\), 818.2 kg N y\({}^{-1}\)), point sources (eight rain sewage collectors, one with illegal inflow of raw wastewater) (192.4 kg P y\({}^{-1}\), 654 kg N y\({}^{-1}\)), atmospheric sources (12.5 kg P y\({}^{-1}\), 50.2 kg N y\({}^{-1}\)) and recreational sources (4.8 kg P y\({}^{-1}\), 97 kg N y\({}^{-1}\)) (Figures 3 and 4).