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Delta-Front Cities as Dynamic Receptors of Microplastic Fluxes: Seasonal Source Switching across Multioutlet Deltas
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Researchers studying Macao's coastal waters found that microplastic pollution levels shift dramatically with the seasons, with certain river outlets in the Pearl River Delta "taking turns" as the main pollution source depending on winds and water currents throughout the year. Microplastic levels in the bay were nearly three times higher than in open water, with particle counts spiking sharply in autumn—meaning coastal communities near river deltas may face far greater exposure through seafood and water at certain times of year than others. This matters because it suggests pollution control efforts need to target the right river sources at the right season, rather than treating microplastic pollution as
Delta-front coastal cities are terminal receptors of riverine microplastics (MPs), yet transport pathways linking multioutlet deltas to nearshore exposure under seasonal hydrodynamic variability remain poorly resolved. Using Macao in the Pearl River Delta (PRD) as a case study, we integrated four-season observations, high-resolution ROMS backward particle tracking, and literature-based fingerprinting. Mean MP abundance in Macao Bay (1.05 ± 1.18 n/m 3 ) was 2.7 times higher than offshore (0.39 ± 0.57 n/m 3 ). Pump sampling revealed subsurface peaks in autumn (up to 15.92 ± 39.58 n/m 3 ). Piecewise structural equation modeling indicated that thermohaline variability regulates vertical sorting. Buoyant PP/PE assemblages (∼45–60%) dominate in summer, while denser PET/PS particles increase in winter. Particle tracking identified a seasonal source-switching pattern: western PRD outlets dominate in winter, whereas the Modaomen outlet contributes most in spring and summer, driven by plume orientation and wind forcing. Literature synthesis corroborates the consistency between modeled pathways and outlet-specific fingerprints. These results suggest that MP delivery is governed by seasonally reconfigured hydrodynamic connectivity rather than static sources. This framework shifts MP attribution from static bulk flux estimation toward dynamically constrained source-pathway-receptor linkages, providing a basis for seasonally targeted MP mitigation in complex deltaic systems.
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Delta-FrontCities as Dynamic Receptors of MicroplasticFluxes: Seasonal Source Switching across Multioutlet Deltas
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Coastal cities near river deltas—like Macao, studied here—collect much higher levels of microplastic pollution in their waters than the open ocean nearby, and researchers found the plastic's source shifts with the seasons depending on winds and water currents. This means efforts to clean up or reduce microplastic pollution in these coastal waters (which people swim in, fish from, and get seafood from) need to target different river branches at different times of year rather than using a one-size-fits-all approach.
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A multi-year study of microplastic contamination in Hong Kong coastal waters identified significant temporal variability linked to seasonal factors, particularly monsoon rainfall and ocean currents from the Pearl River. Microplastic concentrations were highest during and after typhoon season when river discharge and storm runoff peak. The findings suggest that seasonal and meteorological factors must be accounted for when interpreting microplastic monitoring data in coastal Asian cities.
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Researchers measured microplastic abundance, composition, and ecological risk in surface water of the Pearl River Delta across different seasons, finding spatially uneven distribution with some sites showing far higher concentrations than others. Ecological risk scores were highest at sites near industrial zones and dense urban areas.
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