Analysing the influence of hydrodynamic and sedimentary factors on the microplastic distribution in the Ashtamudi estuary, India

This study evaluates the influence of water current and suspended sediment concentration (SSC) on microplastic distribution in various mixing regimes of the Ashtamudi estuary, India. Microplastic abundance ranged from 3.2 to 53 items/L, with highest concentrations observed near the confluence of the river and the sea. Partially mixed regions exhibited elevated near-bottom microplastic concentrations, identifying these zones as potential settling areas. Microplastic abundance showed a direct relationship with SSC and an inverse relationship with current. A non-linear model developed to predict microplastic abundance based on SSC and current demonstrated good performance, achieving an R value of 0.97. This model outperformed the SSC-only model, representing a significant advancement over previous studies. The findings highlight the critical roles of hydrodynamic and sedimentary factors in governing microplastic distribution within the water column. The developed model, after calibration, can be applied to other estuaries globally, supporting plastic monitoring programmes in implementing effective mitigation measures.