What can global hydrological models tell us about sources and flows of riverine plastics?

Plastic pollution is one of the major global water quality issues. Yet the lack of consistent data and standardized monitoring and assessment methods leads to a wide range of uncertainties in estimating the plastic load that is being delivered to marine environments. At the same time, continental and global dynamic hydrological models are becoming more available for large-scale estimation of time-dynamic water fluxes into sea basins. One such tool is a dynamic process-based rainfall-runoff and water quality model Hydrological Predictions for Environment (HYPE) and its global application, World-Wide HYPE (WWH, Arheimer et al., 2020).

Here, we present the first results from simulating global riverine plastic pollution using WWH. The model development is based on the results of the global literature review of sources of microplastics through the lens of a hydrological modeler. Traditional model calibration techniques may not be appropriate in this case due to insufficient number of data points, large variability in plastic characteristics and sampling techniques applied in the collected monitoring studies, as well as large uncertainty and a lack of current knowledge of transport and transformation processes in water bodies. Thus, an ensemble of WWH model setups was developed where the model structure and hydrology is the same and the model parameters that affect generation, transformation, and transport of plastic from various land uses, sanitation categories, and in rivers are varied to explore the defined parameter space. Collected data together with other global estimates were then used to evaluate the ensemble with a weight of evidence approach, highlighting sources and processes of major significance and focusing the ensemble towards a realistic set. Further model error analyses indicate which sources and processes play an important role in transport of riverine plastics as well as how different monitoring approaches can affect the results.

References:

Arheimer, B., Pimentel, R., Isberg, K., Crochemore, L., Andersson, J. C. M., Hasan, A., and Pineda, L., 2020. Global catchment modelling using World-Wide HYPE (WWH), open data and stepwise parameter estimation, Hydrol. Earth Syst. Sci. 24, 535–559, https://doi.org/10.5194/hess-24-535-2020