Three rivers to the test: Lessons for global plastic transport modelling

Area of Science:

• Environmental Science
• Oceanography
• Hydrology

Background:

• Rivers are significant pathways for plastic pollution entering the ocean.
• Global models estimating riverine plastic export face uncertainty due to diverse catchments and complex transport dynamics.

Purpose of the Study:

• To investigate the river-ocean interface and plastic transport dynamics.
• To refine river-to-ocean plastic flux models using empirical data and simulations.
• To understand the impact of diverse riverine conditions on plastic emission.

Main Methods:

• Comparative analysis of three rivers in the Caribbean, Southern Africa, and Southeast Asia with distinct characteristics.
• Deployment of 196 GPS drifters to track surface transport.
• Utilized 41 cameras across six river locations for seasonal monitoring.
• Simulated three years (2020-2022) of plastic transport based on observational data.

Main Results:

• Rivers infrequently flush large amounts of plastic, with 50% of plastic exported within only 7-12% of the time.
• Observed annual average mass fluxes were substantially lower (34-98%) than previous global model estimates.
• Estuaries demonstrate limited capacity for plastic transport.

Conclusions:

• Rivers function as long-term plastic pollution sinks rather than continuous sources.
• Estuarine environments play a minor role in the overall transport of riverine plastics to the ocean.
• Findings highlight the heterogeneity of plastic emission dynamics and the need for context-specific models.