STUDY OF MICROPLASTIC DISTRIBUTION PROCESSES IN THE EASTERN PART OF THE GULF OF FINLAND, BALTIC SEA

Abstract

Monitoring of plastic pollution (macro- and microplastics) in the Gulf of Finland and the Neva Bay has been conducted by the team of authors since 2018, when Dr. Sci. (Phys.-Math.), I. P. Chubarenko initiated the first project for comprehensive scientific study of this problem in the Russian part of the Baltic Sea. In this study, numerical experiments on the distribution of microplastics in the eastern Gulf of Finland under realistic external forcing were conducted using the previously developed high-resolution 3D model by Martyanov et al. (2023) and field data from the Russian State Hydrometeorological University (RSHU) team obtained in 2022. The model takes into account the settling of suspended microplastic particles into bottom sediments by parameterizing the biogeochemical processes of fouling and zooplankton capture. To assess the influence of gravitational sinking velocity on the distribution area of microplastics, four scenarios for the distribution of microplastics from a permanent source in the Neva River estuary are implemented and discussed for four types of microplastics (tracers) with different sinking rates, depending on the season. Two base velocity values of 0.05 m/day and 0.1 m/day are considered. In two experiments, the net velocity is equal to the base velocity throughout the year, while in the other two, the net velocity is calculated taking into account biogeochemical processes in the spring-summer season and is assumed to be zero in the autumn-winter season. It is shown that in the autumn-winter season, microplastics spread the farthest for tracers characterized by zero sinking velocity. Tracers with a constant sinking velocity penetrate into the Gulf of Finland to a lesser extent, and a higher settling velocity leads to less microplastic penetration into the bay. Taking into account biogeochemical conditions in the spring-summer period significantly inhibits microplastic penetration into the bay. The best agreement with in situ measurement data (2022) is observed for a tracer with a constant base settling velocity of 0.05 m/day. An analysis of interannual variability in microplastic distribution in the study area shows that the main external factors determining its distribution are ice cover in the autumn-winter period and river discharge in the spring-summer period.