## 3 Results
### Ordination Analyses  
The general trends and the spatial distribution of the variables correlated with the principal components were analyzed based on the results of the PCA (Figure 4A). Seven hydrological, physical, and chemical parameters which are reliable indicators of ecosystem quality were ultimately selected from the group of 17 environmental variables analyzed in the ordination. One physical parameter (temperature) and 10 chemical parameters (COD, TDS, K\({}^{+}\), Na\({}^{+}\), Mg\({}^{2+}\), Ca\({}^{2+}\), Cl\({}^{-}\), TP, NO\({}_{2}\)\({}^{-}\)-N, and Chl-a) were not included in the model because they were redundant, or did not significantly contribute to the quality of the results.  
The PCA revealed differences in the distribution of nutrients and other water parameters in the evaluated periods (Figure 4B. Both canonical axes explained more than 60% of variance in the period T+0 and 75% in the period T+6. The first axis was most influenced by the concentrations of nitrogen compounds and PO\({}_{4}\)\({}^{3-}\)-P before restoration, and by PO\({}_{4}\)\({}^{3-}\)-P and EC values after restoration. The second axis was most influenced by flow velocity in the T+0 period, and by DO and, partially, by velocities in the T+6 period.  
The PCA analysis comprehensively illustrates the relationships between the studied water parameters, and in particular the negative correlation between flow velocity versus EC and PO\({}_{4}\)\({}^{3-}\)-P (Figure 4A). A comparison of PCA results for the Kwacza River before and after restoration (Figure 4B) revealed the significant role of DO in nutrient removal. A local increase in water flow velocity increased  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{4}{*}{**Load**} & \multicolumn{4}{c}{**Loss of Chemical Elements from the**} & \multicolumn{4}{c}{**Loss of Chemical Elements from the**} & \multirow{4}{*}{**Difference in \%**} \\  & \multicolumn{4}{c}{**(kg\(\cdot\)year\({}^{-1}\cdot\)km\({}^{-2}\))**} & \multicolumn{4}{c}{**(tonnes\(\cdot\)year\({}^{-1}\))**} \\ \cline{2-10}  & \multicolumn{2}{c}{**Kwacza K1**} & \multicolumn{2}{c}{**Kwacza K10**} & \multicolumn{2}{c}{**Kwacza K1**} & \multicolumn{2}{c}{**Kwacza K10**} & \multicolumn{2}{c}{**Kwacza K10**} & \multicolumn{2}{c}{**K1–K10**} & \multicolumn{2}{c}{**K1–K10**} \\  & **(A = 63 km\({}^{2}\))** & \multicolumn{2}{c}{**(A = 85 km\({}^{2}\))**} & \multicolumn{2}{c}{**Kwacza K1**} & \multicolumn{2}{c}{**Kwacza K10**} & \multicolumn{2}{c}{**K1–K10**} & \multicolumn{2}{c}{**K1–K10**} \\ \cline{2-10}  & **T+0** & **T+6** & **T+0** & **T+6** & **T+0** & **T+6** & **T+0** & **T+6** & **T+0** & **T+6** \\ \hline TDS & 116 & 108 & 86 & 80 & 7.308 & 6.804 & 7.310 & 6.800 & 100 & 100 \\ NO\({}_{2}\)-N & 0.02 & 0.03 & 0.01 & 0.02 & 0.001 & 0.002 & 0.001 & 0.002 & 100 & 100 \\ NO\({}_{3}\)-N & 0.45 & 0.36 & 0.33 & 0.12 & 0.028 & 0.023 & 0.028 & 0.010 & 100 & 43 \\ NH\({}_{4}\)-N & 0.15 & 0.17 & 0.26 & 0.13 & 0.009 & 0.011 & 0.022 & 0.011 & 244 & 100 \\ PO\({}_{4}\)-P & 0.15 & 0.13 & 0.11 & 0.10 & 0.009 & 0.008 & 0.009 & 0.009 & 100 & 105 \\ TP & 0.54 & 0.53 & 0.40 & 0.39 & 0.003 & 0.034 & 0.033 & 0.033 & 100 & 100 \\ Cl\({}^{-}\) & 11.7 & 15.8 & 12.9 & 11.7 & 0.737 & 0.995 & 1.097 & 0.995 & 149 & 100 \\ Ca\({}^{2+}\) & 26.6 & 27.5 & 18.4 & 20.4 & 1.676 & 1.733 & 1.564 & 1.734 & 93 & 100 \\ Na\({}^{+}\) & 4.3 & 3.9 & 3.2 & 2.9 & 0.271 & 0.246 & 0.272 & 0.247 & 100 & 100 \\ K\({}^{+}\) & 1.2 & 1.1 & 0.9 & 0.8 & 0.076 & 0.069 & 0.077 & 0.068 & 101 & 99 \\ Mg\({}^{2+}\) & 3.0 & 3.0 & 2.3 & 2.2 & 0.189 & 0.189 & 0.196 & 0.187 & 104 & 99 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Chemical loads carried by the Kwacza River in cross-section terminal sites K1 and K10 before (T+0) and after restoration (T+6).  
water oxygenation and contributed to nitrification. The removal of nitrate-N appeared to be strongly influenced by hydraulic residence time in the restored segments of the river.