SPATIAL DISTRIBUTION AND SEASONAL DYNAMICS OF HYDROCHEMICAL CONDITIONS IN THE VISTULA LAGOON OF THE BALTIC SEA IN 2020–2022

Abstract

To study current hydrochemical conditions in the Vistula Lagoon and the trend of their change under changing anthropogenic impact in 2020–2022 seasonal variability and spatial distribution of hydrochemical parameters (salinity, pH, dissolved oxygen, BOD5, mineral forms of phosphorus and nitrogen) were investigated. The water body is exposed to intense anthropogenic impact from the Kaliningrad agglomeration, the nature of which has undergone qualitative changes in recent years, therefore, a comparative analysis was carried out with the period 2007–2016, which preceded the launch of modern treatment facilities in Kaliningrad. The Vistula Lagoon is characterized by spatial variability of hydrological and hydrochemical conditions, which was considered for 4 different types of regions (eastern, near-Baltic, central and Primorskaya Bay). The impact of anthropogenic factors on the dynamics of hydrochemical conditions had the greatest impact on the eastern region and Primorskaya Bay. The eastern region of the lagoon accounts for the main inflow of nutrients from the catchment area (from the Pregola River), and since 2016 the wastewater outlet from Kaliningrad is located here. Compared to the period before 2016, in the eastern area a significant increase of BOD5, a decrease of dissolved oxygen concentrations, a multiple excess of nitrite and nitrate nitrogen in comparison with the all of the water area lagoon were recorded. In the Primorskaya Bay, where until 2016 low-purity wastewater was supplied from the city of Kaliningrad, in 2020–2022 pollution for most of the studied indicators (BOD5, phosphate phosphorus, ammonium nitrogen) decreased and corresponded to the average values for the water area. The near-Baltic and central regions are strongly affected by natural conditions (sea water inflows), where in 2020–2022, as in the previous period, lower concentrations of nutrients were observed due to the remoteness from the main sources of pollution. Despite the decrease in the intensity of local pollution in the Primorskaya Bay in 2020–2022, the concentrations of mineral forms of nutrients remained at high levels, providing intensive development of algae (including the growth of BOD5) and eutrophication of the Vistula Lagoon.