Variability of concentrations of phosphorus forms under the conditions of weir renovation – The Głuszynka river-lake system case study

To fill the knowledge gap on the functioning of the river-lake system during the modernisation of the weir, an analysis of the variability of selected physico-chemical indicators was carried out. In the parameter analysis, particular emphasis was placed on phosphorus (P) and orthophosphate(V) (OP) content in the hydrological year 2022 and water quality was compared before, during and after the maintenance work on the discharge weir. Physico- chemical parameters were analysed monthly at four stations. Concentrations of P and OP increased significantly as a result of the refurbishment works at the measurement point located downstream of the weir (P4), which contributed to the determination of a statistically significant change point. At the same time, when high P and OP contents were observed, high electrolytic conductivity and ammonium nitrogen in water were also recorded. The content of P and OP indicators was further reduced, but their content was still several times higher than before the renovation. The renovation of the weir below Lake Jeziory Wielkie contributed to a significant deterioration of water quality in the river-lake system. Due to the nature of this system, this was of great importance for the downstream reservoirs. The statistical analysis showed that the renovation of the weir below Lake Jeziory Wielkie contributed to a significant deterioration of water quality in the river-lake system.