Influence of Hydrometeorological Conditions on the Plankton Distribution in the Estuary of the Pregolya River and the Coastal Part of the Baltic Sea

Abstract

The patterns of changes in the composition and quantity of zooplankton and concentration of chlorophyll a in the estuary of the Pregolya River and adjacent waters of the Baltic Sea are considered depending on hydrological and meteorological conditions in 2021–2022. Three zones of the estuary were identified: estuarine, mixing, and marine. In the water mixing zone, there are salinity gradients, the position of which is influenced by wind forcing and river discharge. The largest concentration of chlorophyll a was noted in the estuarine zone and at the boundary of the water mixing zone, where the flow of nutrients from the drainage area is most noticeable. The removal of water from the lagoon affects the concentration of chlorophyll a and the composition of zooplankton. The estuarine zone is characterized by the highest level of eutrophication, where it approaches the threshold of hypertrophy; in the marine zone, the concentrations of chlorophyll a corresponded to eutrophic water. Depending on the inflow–outflow phenomena, the proportion of zooplankton species differs in relation to changes in salinity, and there is a sharp increase in deaths of organisms of species not adapted to a given salinity.