Micro- and Mesoplastic Monitoring on Beaches: Understanding Seasonal and Spatial Distribution Patterns

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Abstract
Despite growing research on microplastic contamination in beach environments, the factors influencing pollution distribution remain poorly understood. This study aims to bridge this knowledge gap by investigating microplastic pollution across 11 Latvian marine beaches (northeastern Europe). The study area experiences a four-season climate and is influenced by the Gulf of Riga and the Baltic Sea. Beaches were selected based on prior research (Dimante-Deimantovica et al., 2023), and data collection took place from autumn 2022 to summer 2023.Microplastic samples were collected seasonally - autumn, winter, spring, and summer - across three distinct 100 m transects at each beach: the waterline (closest to the sea), the mid-section (between the waterline and vegetation), and the area in front of vegetation or bluffs (farthest from the sea). The results revealed seasonal variations in microplastic abundance, with higher pollution levels observed in autumn and winter compared to spring and summer. Furthermore, plastic particle distribution was uneven across the transects, with vegetation occasionally acting as a barrier for microplastic accumulation. Rounded particles are wind-transported and gather near vegetation, while longer particles accumulate already in the first transect near the sea. This study emphasizes the importance of year-round sampling to ensure accurate pollution assessments in environments with pronounced seasonality. Considering seasonal variability is also crucial when interpreting and comparing existing monitoring results.The research is supported by GRANDE-U project “Groundwater Resilience Assessment through iNtegrated Data Exploration for Ukraine” (NSF Awards No. 2409395/2409396) and Latvian Environmental Protection Fund project No. 1-08/37/2022.Reference: Dimante-Deimantovica, Inta et al. (2023) The baseline for micro- and mesoplastic pollution in open Baltic Sea and Gulf of Riga beach. Frontiers in Marine Science. https://doi.org/10.3389/fmars.2023.1251068