## 3 Results
### Results of Phosphorus Adsorption Experiments
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Tested Adsorption** & **Characteristic** & \multicolumn{4}{c}{**Sediment Layer**} \\ \cline{3-6}
**Model** & & **0-5 cm** & **5-10 cm** & **10-15 cm** & **15-20 cm** \\ \hline \multirow{3}{*}{Freundlich} & 1/n & 1.374 & 1.615 & 1.293 & 1.164 \\ \cline{2-6}  & K [dm\({}^{3}\) kg\({}^{-1}\)] & 1893.093 & 2736.946 & 3693.590 & 3291.355 \\ \cline{2-6}  & R\({}^{2}\) & 0.9825 & 0.9843 & 0.9709 & 0.9871 \\ \hline \multirow{3}{*}{BET} & S\({}_{\text{SET}}\) [mg P kg\({}^{-1}\)] & 15,649.34 & 7153.802 & 354.64 & 425.638 \\ \cline{2-6}  & k\({}_{\text{SET}}\) [dm\({}^{3}\) mg\({}^{-1}\)] & 0.23 & 0.158 & 7.2073 & 6.39 \\ \cline{2-6}  & C\({}_{\text{s}}\) [mg dm\({}^{-3}\)] & 3.44 & 1.444 & 0.5623 & 0.6169 \\ \cline{2-6}  & R\({}^{2}\) & 0.9707 & 0.9892 & 0.9952 & 0.9962 \\ \hline \multirow{3}{*}{General
\begin{tabular}{c} Freundlich- \\ Langmuir \\ \end{tabular} } & S\({}_{\text{FL}}\) [mg P kg\({}^{-1}\)] & 2121.286 & 37,641.93 & 45,343.34 & 18,634.84 \\ \cline{2-6}  & k\({}_{\text{FL}}\) [dm\({}^{3}\) mg\({}^{-1}\)] & 1.741 & 0.21 & 0.14 & 0.26 \\ \cline{2-6}  & 1/n (\(\alpha\)) & 2.547 & 1.64 & 1.26 & 1.21 \\ \cline{2-6}  & R\({}^{2}\) & 0.9985 & 0.9837 & 0.9701 & 0.9859 \\ \hline \multirow{3}{*}{Other parameters} & S\({}_{\text{0}}\) [mg P kg\({}^{-1}\)] & 20.08 & 6.61 & 0.26 & 0.22 \\ \cline{2-6}  & EPC\({}_{\text{0}}\) [mg dm\({}^{-3}\)] & 0.037 & 0.023 & 0.0004 & 0.0003 \\ \cline{1-1} \cline{2-6}  & \(\Delta\)G [k] mol\({}^{-1}\)] & \(-\)16.07 & \(-\)16.46 & \(-\)19.81 & \(-\)20.38 \\ \cline{1-1} \cline{2-6}  & P retention [\%] & 99.25 & 99.35 & 99.62 & 99.63 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: P adsorption characteristics of bottom sediment of Lake Kortowskie at St. 1 (control). The range of native adsorbed P (S\({}_{0}\)) for analyzed deposits was between 20.08 and 0.22 mg P kg\({}^{-1}\) DW (St. 1) and between 21.23 and 2.97 mg P kg\({}^{-1}\) DW (St. 2), with maxima for the surficial deposits (0-5 cm) at both stations. These parameter values declined with sediment depth. A similar situation was observed for P equilibrium concentrations EPC\({}_{0}\). Higher values of this parameter were noted for upper sediment layers (Tables 3 and 4), but the assessed EPC\({}_{0}\) was very low for analyzed sediments. Calculated Gibbs free energy was rather low, between \(-\)15.19 kJ mol\({}^{-1}\) (St. 2, deposit layer 5-10 cm) and \(-\)20.38 kJ mol\({}^{-1}\) (St. 1, layer 15-20 cm). This order of magnitude confirms the physical type of observed P adsorption. Despite this, the noted P retention by Lake Kortowskie sediment was very high and varied between 98-99% (Tables 3 and 4). All assessed adsorption characteristics were subjected to statistical analysis (\(t\)-test) to find the differences between research stations, but the obtained results revealed that significant differences in P retention only between St. 1 and St. 2 were found (t-value 2.88, n = 8, \(p\) < 0.02). The performed RDA analysis showed that the main factors connected to physical P adsorption characteristics by the bottom sediment of Lake Kortowskie were organic matter (and also TN, because sedimentary nitrogen is deposited mainly in organic form), iron, and manganese, while aluminum, silicates, calcium carbonates, and TP showed no significant connections. OM was correlated with BET model characteristics (positive correlation with single monolayer capacity (S\({}_{\rm BET}\)), adsorbate saturation concentration for single monolayer (Cs), native sorbed P (S\({}_{0}\)), and negatively correlated with iron content (positively correlated with k\({}_{\rm BET}\)). A less weak correlation was found with free Gibbs energy, k\({}_{\rm fil}\), and 1/n\({}_{\rm fil}\) (constants in the general Freundlich-Langmuir equation). EPC\({}_{0}\) (P equilibrium concentration) and 1/n (Freundlich equation constant) parameters were positively correlated with manganese content in the sediment. Two main axes explained 99.8% of the variability (Figure 10).