Spatiotemporal Dynamics of Anthropogenic Macro-Litter in Lotic and Lentic Freshwater Ecosystems of the Southeastern Black Sea

Abstract

This study investigated the seasonal distribution, density, and composition of macro-litter in the lentic and lotic ecosystems in the southeastern Black Sea region of Türkiye. Seasonal sampling was conducted throughout 2025 in Arılı (4 stations) and Çağlayan (3 stations) streams and the Muratlı Dam Lake (4 stations). To quantify pollution dynamics, the litter items (>2.5 cm) were collected within 100 m2 transects along riverbanks and reservoir coasts. The collected items were categorized into nine primary classes following the Guidance on Monitoring Marine Litter in European Seas. The resulting data were evaluated using non-parametric statistics. Litter items were observed among all the sampling stations during the surveys, with a significant spatial heterogeneity. Litter items were observed among all the sampling stations during the surveys, with a significant spatial heterogeneity. The highest litter densities were determined at stream-mouth stations, reaching 4.70 items/m2 in Arılı and 4.32 items/m2 in Çağlayan. Muratlı Dam Lake exhibited the highest overall litter accumulation (1.77 ± 0.17 items/m2), significantly exceeding Arılı (0.91 ± 0.34 items/m2) and Çağlayan (1.25 ± 0.43 items/m2). Seasonal fluctuations were particularly pronounced in Muratlı Dam Lake, where litter density increased from 1.24 ± 0.05 items/m2 in winter to 2.80 ± 0.21 items/m2 in spring due to intensified rainfall, snowmelt, and runoff-driven transport processes. Plastics overwhelmingly dominated litter composition across all seasons and locations, accounting for 65.5–80.1% of the total litter items, while cigarette butts (24.2%), and tear-off plastic bags (9.1%) represented the most abundant litter subcategory. These findings highlight the need for integrated watershed management and public awareness to curb upstream plastic pollution and secondary microplastic generation. Addressing this transboundary challenge requires robust international collaboration and long-term monitoring of regional hydrological changes.