Microplastic dynamics in Ramsar-declared wetlands: a case study of Makuleke and Nylsvley, South Africa.

Abstract

Microplastic pollution has emerged as a pervasive environmental challenge, threatening freshwater ecosystems and biodiversity worldwide. Despite extensive studies on marine systems, research on freshwater wetlands, particularly in Africa, has been limited, with these ecosystems playing vital roles in biodiversity conservation, nutrient cycling, and water purification. This study investigated the abundance, distribution, and characteristics of microplastics in two Ramsar-declared wetlands in South Africa, Makuleke (Kruger National Park) and Nylsvley Nature Reserve (Limpopo Province), across contrasting hydrological seasons (wet and dry). Water, surface sediment, and sediment core samples were collected and analyzed using density Separation and Fourier Transform Infrared (FTIR) spectroscopy to identify the types and morphologies of microplastic polymers. The results revealed substantial microplastic contamination in both wetlands, with sediments acting as major sinks. Fibres, fragments, and beads were the dominant morphotypes, while black, transparent, and white were the most common colours detected. The Nylsvley Wetland exhibited higher microplastic abundance and ecological risk levels compared to Makuleke, reflecting stronger anthropogenic influences from adjacent agricultural and peri-urban activities. Seasonal variation was evident, with significantly high concentrations of microplastics during the wet season, primarily due to increased hydrological transport and runoff. Sediment core analysis further indicated that microplastic deposition patterns were influenced by sediment composition and hydrodynamic conditions, suggesting long-term accumulation and potential remobilisation during flood events. This study presents the first comparative assessment of microplastic dynamics in Ramsar-designated wetlands in South Africa, providing valuable baseline data for future monitoring efforts. The findings highlight that even protected ecosystems are vulnerable to diffuse emerging pollutants such as microplastics. Effective mitigation requires integrated catchment management, improved waste disposal practices, and continued monitoring of both surface and sedimentary microplastic loads. Overall, the study highlights the ecological significance of wetlands in regulating microplastic transport and emphasizes the importance of integrating plastic pollution management into wetland conservation policies.