## 4 Discussion
The results of PCA clearly point to a nitrogen-limited system rather than a phosphorus-limited system. The extent to which each of the above factors contributed to the observed improvement is difficult to assess; however, the restoration project decreased annual loads of TDS by 510 kg, Cl\({}^{-}\) by 102 kg, Na\({}^{+}\) by 25 kg, NO\({}_{3}\)-N by 18 kg, and NH\({}_{4}\)\({}^{+}\)-N by 11 kg (Table 6). No significant changes in TP or PO\({}_{4}\)\({}^{3-}\)-P removal were observed. The restoration project significantly contributed to nitrate-N loss, not only between the compared years, but also along the restored river section after restoration (Figures 3 and 5, Table 6). Above all, the restoration system contributed to the removal of 57% of nitrate-N, which decreased N loads by 12 kg per year. In the group of analyzed parameters, Cl\({}^{-}\) is generally considered as a conservative element, and consequently, a good indicator of geochemical changes. However, in catchments located in the vicinity of the sea, changes in Cl\({}^{-}\) concentrations may result from catchment-derived factors--mainly groundwater supply. In the Kwacza River (30 km from the sea), the change in Cl\({}^{-}\) in the restored segment was similar to that noted before restoration, which indicates that the catchment was a source of this element. It is worth noting that buffer zones composed of riparian vegetation are most effective in preventing agricultural pollutants from entering the river. According to many authors, the width of the buffer zone plays the most important role in protecting water quality [57; 58; 59]. The pH of water is determined mainly by the presence of aquatic vegetation, which is why pH was lowest near stone islands and in insolated areas strongly overgrown by _Rannuculetum aquatilis_. Nutrient concentrations are highly correlated with the growth of aquatic vegetation, and the highest nutrient levels were observed in the cut-off channel by the culvert in T+6. This applied hydrotechnical solution induced the greatest changes in WQ parameters (Table 4). The construction of the by-pass promoted the emergence of a new microhabitat composed of lush _Callitriche cophocarpa_, _Sparganium emersum_, and _Batrachium aquatile_ vegetation. These types of hydrotechnical treatments reduce channel width and promote the mixing of water and bottom sediments. Assessments of restoration techniques should also account for the lag between stream restoration and the corresponding changes in water quality. In our approach, monitoring was continued six years after project completion, as recommended by [PERSON] [31], to determine whether the restored river system had been effectively stabilized and adapted to external disturbances such as floods, changes in land use, and agricultural treatments in the catchment. This study revealed changes in the physicochemical parameters of the Kwacza River already after the first stage of the restoration project when the riparian system had not yet been fully stabilized. Our results indicate that continuous and discrete monitoring of the Kwacza River supports effective prediction of the relationships between monitoring sites and habitats, and the identification of the most effective biological indicators. We are convinced that longer-term monitoring can facilitate assessments of other planned enhancements and their influence on water quality and quantity in the catchment. Our findings contribute to the discussion on the effectiveness of restoration projects in improving the quality of aquatic ecosystems in agricultural catchments.