Large variation in Mekong river plastic transport between wet and dry season

Plastic pollution in rivers is of increased global concern. Rivers act both as pathways for land-based plastic waste into the ocean, and reservoirs long-term retention. Reliable observations are key to designing, optimizing evaluating strategies prevent reduce pollution. Several measurement methods have been developed quantify macroplastic ( > 0.5 cm) storage transport rivers, including visual counting from bridges, net sampling, images-based techniques. Method harmonization crucial make sure data collected using different techniques remains consistent. In turn, this would allow comparative analysis within between rivers. paper, we present a approach estimate floating item mass methods. The allows estimating same values based on collection protocols. We applied our Mekong-Tonlé Sap-Bassac river system around city Phnom Penh, Cambodia. estimated wet dry season by combining sampling counting. During season, Mekong with factor up 170 (item transport) 294 (mass compared season. balance Penh changed considerably, which was mainly due flow reversal Tonlé Sap Downstream total consistently higher than upstream, although less (1.5–1.7 times) (3.8–5.9 times), emphasizing city’s role entry point Mekong. largest sources uncertainty assumed be caused differences methods, size ranges, extrapolation observation full width, contribution submerged transport. Future work should focus other counting, reducing uncertainties related Our results show that dynamics highly variable over time space, especially confluences, bifurcations urban areas. With paper aim contribute further monitoring.