Abstract
Microplastic pollution is an emerging concern for freshwater ecosystems, yet urban
wetland systems in South Africa remain largely unstudied. Microplastics are plastic
particles smaller than 5 mm that can disrupt ecological processes, accumulate in
organisms, and reduce water quality. Shallow, seasonally variable wetland pans are
particularly vulnerable because they are located in rapidly urbanising and
industrialising landscapes. These wetlands provide essential ecosystem services,
including water storage, nutrient cycling, and habitat provision, but little is known about
the extent, sources, or behaviour of microplastics in these systems. This study aimed
to examine the seasonal and spatial distribution of microplastic pollution in four urban
wetland pans in southeastern Gauteng namely the Bullfrog, Korsman, Sand, and
Blaauw pans. Water, sediment, and macroinvertebrates (Chironomus spp.) were
sampled across wet and dry seasons to provide a multi compartmental perspective of
contamination. Standardised methods were applied to ensure comparability across
sites. Samples were processed using potassium hydroxide digestion and classified
following the MSFD guidelines. Polymer composition was determined using
attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR).
Water quality parameters including pH, salinity, conductivity, temperature, and nutrient
concentrations were measured to contextualise observed microplastic patterns.
Sediment grain size was analysed to examine the influence of particle size and
sediment characteristics on microplastic accumulation. Geographic information
system analyses and land use mapping were used to identify potential sources and
hotspots of contamination, integrating data on urban and industrial expansion between
2014 and 2024.
Microplastics were detected in all components, at all sites, across the water and
sediment samples in both seasons. Filamentous microplastics were the most common
form, with blue and black fibres frequently observed in water and sediment.
Chironomids showed similar uptake patterns, demonstrating their potential as
bioindicators of microplastic exposure. Polymer identification revealed polyethylene
terephthalate, cotton, and nylon as the most common types, implicating textiles,
wastewater inputs, and urban runoff as primary sources. Seasonal trends varied
among the pans. Korsman Pan showed higher microplastic concentrations during the
wet season, whereas Bullfrog and Blaauw pans had higher concentrations in the dry
season. Summer conditions were associated with higher salinity, pH, and conductivity,
while winter conditions favoured clearer water and finer sediment textures. Nutrient
concentrations were highest in Sand and Bullfrog pans, likely reflecting localised
effluent discharge and stormwater inputs. Statistical analyses revealed correlations
between microplastic abundance and abiotic parameters such as water clarity, salinity,
and temperature, highlighting the interaction between natural seasonal cycles and
anthropogenic pressures. Long term land use changes showed progressive wetland
contraction during drier years, as well as increased erosion in the Sand and Blaauw
pans. These landscape changes, together with seasonal vegetation fluctuations,
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appear to influence both the mobilisation and accumulation of microplastics,
demonstrating the complex pathways through which microplastic pollution enters and
moves within urban wetland systems.