The effect of estuaries on plastic transport from river into the sea

Rivers play an important role in the global distribution of plastic pollution. Plastics are both retained within river systems, and emitted into the ocean. The net transport of plastic from rivers into the sea is determined by the transport processes within the estuary, which connect the freshwater and marine environments. Estuarine plastic transport and retention dynamics are the combined effect of tidal dynamics, freshwater discharge, and river morphology. Despite its crucial position within the global plastic budget, the effect of estuaries on plastic transport from rivers into the ocean remain unresolved. In this presentation, we provide an overview of estuarine plastic transport and retention dynamics across rivers in Europe and Asia. We extended a simple method [1] to estimate the net transport per tidal cycle, based on surface plastic observations, plastic concentration measurements, and modelled river discharge. Net plastic transport varies strongly with considered time scale, ranging from a single tidal cycle to a full year. Furthermore, we show net transport is impacted by the strength of the tidal dynamics, freshwater discharge, level of plastic pollution, and other river characteristics. Our results demonstrate across timescales, only a limited portion of river plastic pollution may exported into the ocean. The remainder is hypothesized to accumulate on riverbanks, in vegetation, and at other elements within the riverscape [2]. During spring tides and limited freshwater discharge, the net plastic export can be negative, transporting more items from the sea into the estuary. These findings are in line with recent observational evidence of high plastic retention in rivers, and limited net transport from rivers into the sea [3]. This presentation aims to contribute to a better understanding of the global plastic flows from land to sea. Through better understanding the effect of estuaries on river plastic transport, we aim to contribute to improved monitoring, quantifying, and reduction of plastic pollution in the environment.

 

References

[1] Schreyers, L.J., et al. "River plastic transport affected by tidal dynamics." Hydrology and Earth System Sciences 28.3 (2024): 589-610.

[2] van Emmerik, T.H.M., et al. "Rivers as plastic reservoirs." Frontiers in Water 3 (2022): 786936.

[3] Lotcheris, R.A., et al. "Plastic does not simply flow into the sea: River transport dynamics affected by tides and floating plants." Environmental Pollution 345 (2024): 123524.