## 3 Results and Discussion  
### Changes in Oxygen Distribution in Near-Bottom Waters during the Research Period  
The results of the research on oxygenation in the tropholytic zone in Lake Lajskie, carried out around the devices of the oxygenation system, are presented in Tables 2 and 3 and Figures 4 and 5. Figure 4: Changes in oxygenation of the waters of Lake Lajskie at a depth of 0.5 m (a) and 1.0 m (b) above the bottom level. In the period preceding the launch of oxygen dosing, in May 2021, clear deoxidation of the water was already noted in the bottom layers. Most of the measuring stations were characterized by the oxygen content not exceeding 0.1-0.2 mg L\({}^{-1}\), and virtually no oxygen was found around the deepest fragments of the bottom (Tables 1 and 2). The area to the south-east of reactor no. one, located in the shallowest location, i.e., on the border of the 6 m isobath in the place of the fastest shallowing of the bottom (Figure 3), was characterized by slightly better conditions. The average oxygen content in the water for this area was 0.73 and 0.82 mg L\({}^{-1}\), respectively, 0.5 and 1.0 m above the bottom. By starting the oxygenation process in the lake, the oxygen content around all aerators was increased. On average, the average oxygenation was at a level of 1-1.5 mg L\({}^{-1}\) in the layer 0.5 m above the bottom and 1.5-2.0 mg L\({}^{-1}\) at a distance of 1 m from the bottom sediment level (Figure 4). The highest average concentrations in both analyzed layers were also obtained around the shallowest reactor no. one. A more detailed analysis of the obtained results shows that the differences in oxygen concentrations at individual 12 measurement points around each device were high (Tables 2 and 3). The highest values were found, without exception, at the stands closest to the aerator, but these were always stands opposite the oxygenated water outlets. At the points closest to the aerator, but  
Figure 5: Oxygen content around the application devices, in the near-bottom water (0.5 m above the sediment). opposite to the water intake, the oxygen content did not increase so rapidly, which is confirmed by the mechanism of oxygen transport along with the moving water masses. This was in accordance with the assumed directions of water discharge outlets indicated in Figure 1.  
The results of the statistical analysis confirm these observations. Both tested variables (distance from reactor and direction in which reactor released oxygen) were highly significant (\(p<0.000000\)). The assessed model showed good fit to experimental data (R\({}^{2}\) = 0.821, R = 0.675, \(n\) = 96). The obtained regression equation was as follows:  
\[\mathrm{Y}=1.21\,-\,0.92\;\mathrm{D_{r}}-\,0.60\;\mathrm{D_{i}}+\mathrm{E_{ij}}\]  
It means that both tested factors have influence on oxygen concentration in restored area of lake. Oxygen decreased with distance from aerator, as well as direction of oxygen releasing shaped oxygen conditions. For a more complete picture of the mosaic of oxygen conditions in the water of the lower layers in the tropholytic zone of the lake, a graphic summary of the results of research works in the peak period of the summer season was prepared (Figure 5). The comparison of changes in the oxygen content at individual stations after the start of oxygenation (June) and after about 2 months of system operation made it possible to obtain valuable information about the changes taking place in the experimented environment. The general tendency was an increase in the average oxygen content around individual aerators in August (Figure 4); however, it was not a phenomenon accompanying the entire research area. The analysis of individual measuring points showed that in water at test stands located usually on the edge of the oxygenation area (e.g., stands 5-6, 11-12 around aerators no. 1 and no. 2, stands 7-8 around aerator no. 5), after the initial increase in oxygen concentration in June, deterioration of oxygenation conditions was noted in August.