Modelling Microplastic Transport in River Systems Using the SWAT Hydrological Model

Microplastic pollution remains a global environmental threat due to its persistence and widespread occurrence, as well as ecological impacts on freshwater systems. An understanding of the matrix and processes of microplastic transport prevailing through river basins is important for planning mitigation regulations and activities. This paper presents a novel modelling technique for modelling microplastic transport in river basins and proposes the Soil and Water Assessment Tool (SWAT) hydrological model as a promising avenue to aggregate the process of microplastic transport through river systems. Our SWAT adaptation incorporates microplastic release sources, hydrology, and sediment transport processes, allowing for the representation of microplastic spatial and temporal distributions in various sub-basins across the landscape. Model calibration created no-observed hydrology and water quality data and transport dynamics validation used microplastic concentrations. Our results illustrated that land use, precipitation intensity, and surface runoff were all pertinent for mobilising and depositing microplastics. We established that microplastics are made available to rivers primarily through agricultural practices and urban runoff, and are further transported downstream mainly by sediment resuspension. Overall, our study represents a significant enhancement in the application of process-based hydrological models towards microplastic research. We also provide strong scientific support for watershed management practices with expressed intent in reducing plastic pollution in riverine environments.