From River to Sea: Tracking Plastic Waste Transport via the Hau River, Mekong Delta, Vietnam

Plastic pollution in river systems is a growing concern, especially in the Mekong Delta, where complex tidal dynamics facilitate downstream transport of plastic waste into the marine environment. This study assessed the density, composition, and temporal variability of floating plastic waste in the Hau River, approximately 30 km upstream of the Tran De River estuary. Floating net traps were deployed during both ebb and flood tides to quantify plastic waste with simultaneous meteorological and hydrological monitoring. The findings highlight that key meteorological factors, such as air temperature, humidity, wind speed, and wind direction, were found to indirectly influence plastic transport by altering surface currents and promoting plastic degradation. Meanwhile, hydrological conditions, especially tidal variability, play a direct and dominant role in determining the spatial and temporal distribution of plastic waste. Plastic debris was diverse in terms of items during both tidal phases. Although the number of plastic pieces was higher at ebb tide (134.33 pieces/h), the volume and concentration of plastic were greater at flood tide (1.22 kg/h and 0.73 kg/m3) than at ebb tide (0.81 kg/h and 0.29 kg/m3). Macroplastic debris was almost dominant during both ebb tide (97.29%) and flood tide (93.96%) compared to megaplastic and mesoplastic size. These findings highlight the importance of integrating tidal and climate factors into plastic waste management and support targeted interventions to reduce plastic discharge into coastal ecosystems.