An integrated modeling framework for riverine macroplastic emissions, transport, and accumulation across the land-sea...

Plastic pollution in coastal environments is shaped by interactions among land-based emissions, river networks, and marine hydrodynamic processes, yet these processes are rarely examined within a unified approach. Here, we present an integrated source-to-sink modeling framework for macroplastic pollution across the river-sea continuum, coupling a spatial probabilistic model with the 3D SHYFEM hydrodynamic model and its Lagrangian particle-tracking module. Applied to the Venice Lagoon and adjacent northern Adriatic Sea, the framework quantifies how plastics are mobilized from land, transferred through river networks, and redistributed within coastal waters. The probabilistic component resolves spatiotemporal variability in riverine emissions by combining mismanaged plastic waste with meteorological, land-use, and hydrological drivers, while the hydrodynamic-Lagrangian component simulates transport pathways and accumulation patterns. Results show heterogeneous and seasonally variable riverine inputs, with baseline annual emissions of 4.23 × 10⁴ kg yr^-1. The Brenta River contributed 37.3% of annual emissions, followed by the Sile (12.2%) and Dese (9.8%), while the top six rivers accounted for more than 80% of the total load. Source intensity strongly affected the magnitude and seasonal expansion of model-predicted potential accumulation zones, whereas their spatial distribution remained stable, indicating that hydrodynamic processes primarily controlled accumulation patterns. Simulated hotspot extent increased by 22% under the high-load case and decreased by 63% under the low-load case, although these model-predicted patterns require targeted field validation. The framework links inland emissions to coastal fate and supports the identification of key emission areas, transport pathways, and persistent accumulation zones to inform mitigation in river-dominated coastal systems.