2023 Issue №3

Submarine discharge of groundwater (SDGW) is a hydrological process that typically occurs in coastal areas and is defined as the underwater inflow of fresh and brackish ground­water from the continent to the sea. The discharge of waters with a composition sharply differ­ent from seawater leads to the formation of hydrochemical anomalies in the near-bottom hori­zon and alters the composition of bottom sediments. Under different regional conditions, dis­charge can occur as a focused flow through cracks in karst and fissured rocks, as a diffuse flow in loose deposits, or through the recirculation of seawater in bottom deposits. Therefore, it is essential to consider local geological and hydrogeological conditions, as they can significantly influence the character and distribution of groundwater and, consequently, the possibility of submarine discharge and the likelihood of its detection. Despite the ubiquity of the SDGW process in the continental shelf zone, practical detection is often a challenging task. The aim of this study is to identify approaches that best allow for documenting the phenomenon of sub­marine discharge of groundwater in the southeast part of the Baltic Sea. Detecting submarine groundwater discharge in the Baltic Sea is crucial for understanding the processes in the wa­ter body and evaluating the ecological situation. The study examines various methods for detecting SDGW: computational-analytical, geophysical, radioisotopic, chemical, and biologi­cal. The expe­rience of their application in the southeastern Baltic Sea is characterized, allow­ing for the identi­fication of areas where submarine discharge of groundwater from Jurassic and Cretaceous hori­zons occurs. The conclusion is drawn that for effective detection of sub­marine discharge foci, a comprehensive approach involving various research methods is neces­sary.

The Vistula Lagoon is a transboundary lagoon of the Baltic Sea that is subject to signifi­cant pollution and water eutrophication. An assessment of the ecological condition of the la­goon was conducted based on the calculation of modern Russian and foreign water pollution indices for the period 2007—2022. The long-term variability of these parameters was ana­lyzed for the lagoon as a whole and separately for four regions characterized by specific condi­tions. The highest level of water pollution is characteristic of the eastern region and the Pri­morskaya Bay. The Russian Water Quality Index (SCWPI) and the widely used world index, the Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI), demonstrated similar seasonal and long-term variability. The launch of modern treatment facilities in 2016 led to a significant reduction in pollution in the Primorskaya Bay. However, in recent years, an increase in pollution has been observed in the eastern region, where the main river runoff (from the Pregolya River) enters and where the new discharge of Kalinin­grad's treatment facilities is located. The level of eutrophication and phytoplankton abun­dance (chlorophyll concentration) influences the calculated water pollution indices (SCWPI and CCME WQI). The highest values were observed during the period of "water bloom" in the lagoon. The introduction of filter-feeding mollusks and the resulting changes in the plank­ton of the Vistula Lagoon have contributed to the reduction of water pollution indices.