<![CDATA[Microplastics (MPs) are ubiquitous contaminants in river-estuary systems but their distribution in the water column vs surface sediments in tropical regions is still poorly understood. The present study aims to investigate the spatial and temporal distribution of MPs abundance and properties in water and surface sediments at the Jawi River–Kakap Estuary, West Kalimantan, Indonesia. Sampling was carried out at 17 sites including upstream residential areas, middle sections and the estuarine zone during June to August in 2025. MPs levels in surface sediments were generally higher than those in the water column during the study. Fibres were the most abundant particle type in the water with a maximum concentration of 161 particles, while fragments were the dominant particle type in the surface sediments with a maximum concentration of 1,250 particles, indicating that these depositional areas are sites of significant accumulation. The Kruskal-Wallis test revealed significant differences in MPs types between water and sediments for all the months of sampling (p < 0.001). However, significant spatial differences between the upstream (PT), middle-reach (KR), and estuarine (SK) station groups were detected only in the water column during June (H = 10.90, p = 0.004) and July (H = 7.05, p = 0.030), but not in sediments. Transparent particles dominated both water and sediments, but sediment samples contained a greater variety of colours. These results indicate that the water column responded more promptly to the spatial heterogeneity of MPs input and transport, while surface sediments presented more extended periods of accumulation.]]>
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