Model-based estimation of microplastic stock in China’s reservoirs: A continental assessment

Reservoirs act as important vectors for land-to-ocean plastic transport and long-term sinks for plastics, where the accumulation of microplastics poses potential risks to the freshwater ecosystems. Despite increasing public concern about microplastic pollution in reservoirs, it remains challenging to conduct large-scale assessments of microplastic stocks in reservoirs required for developing effective mitigation, due to the large amount of labor needed in the microplastic sampling and analysis and the data incomparability among the existing microplastic data. To address this gap, here we introduce a modeling approach based on geographically distributed plastic waste in the reservoir-specific watershed and reservoir characteristics to estimate the microplastic stock in freshwater reservoirs. Microplastic data in global reservoirs were first collected and screened based on their reliability scores, followed by realigning the abundance to the full microplastic continuum (1–5000 μm). Combined with reservoir capacity and watershed plastic waste data, the microplastic stocks in reservoirs formed the dataset for model development, which was partitioned into the calibration (n = 42) and validation (n = 49) sets. The model achieves a goodness-of-fit of 0.79 for the calibration set and 0.833 for the validation set, to predict the microplastic number stock. Regarding the microplastic mass stock, the goodness-of-fit is 0.76 and 0.826 for the calibration and validation sets, respectively. We subsequently apply this model to estimate microplastic stocks in China’s reservoirs. We estimate that ∼ 10 (range: 2.5–24.7) thousand metric tons of microplastics are present in the reservoir surface waters in China, with large-scale reservoirs accounting for the majority of microplastic stock. The applicability of our approaches goes beyond the context of reservoirs in China, potentially enhancing the understanding of the plastic pollution state in global reservoirs.