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Rivers as microplastics gatekeepers: Linking terrestrial inputs to coastal sediment sinks and sources
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Researchers measured microplastics in riverine and estuarine sediments across seasons in an urban Chinese coastal system, finding that riverine sediments held roughly 2.7 times more microplastics than estuarine sediments, and that a typhoon-driven discharge event flipped the estuary from a net sink to an active source by resuspending and exporting accumulated particles.
Coastal sediments are widely recognized as a critical barrier regulating the transfer of contaminants, particularly microplastics (MPs), from terrestrial environments to marine ecosystems. However, whether these sediments function primarily as long-term sinks or as episodic sources of MPs, and the mechanisms governing this functional transition, remain poorly constrained. This study investigated the key drivers controlling the seasonal and spatial distribution of MPs in coastal sediments within a densely populated urban river-to-sea system. The average MP abundance in riverine sediments was 55.63 ± 38.11 items/kg, approximately 2.7 times higher than that observed in estuarine sediments at 20.93 ± 13.08 items/kg, indicating that riverine inputs constitute the dominant source of MPs to the estuarine and coastal environment. Polyethylene and polypropylene - were the dominant plastic types in both water and sediment samples. Seasonal variations in MP accumulation within estuarine sediments were closely associated with changes in river discharge, sediment resuspension, and local hydrodynamic conditions. The lowest MP abundance occurred in autumn following a typhoon-induced extreme discharge event, suggesting that high-energy hydrological forcing mobilized and exported previously accumulated MPs from riverine and outfall-related sediments, thereby shifting sediments from temporary sinks to active sources. These findings demonstrate that sedimentary MP inventories are highly dynamic rather than static, responding sensitively to episodic hydrological disturbances and coastal engineering structures. By explicitly linking terrestrial inputs, current directions, extreme discharge events, and sediment dynamics, this work advances mechanistic understanding of when and how coastal sediments alternate between acting as sinks and sources of MPs in river-to-sea continua.
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Sinks and sources: Assessing microplastic abundance in river sediment and deposit feeders in an Austral temperate urban river system
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Researchers investigated microplastic abundance in river sediments and depositional zones, finding that sediment acts as both a sink and a temporary source, with stored microplastics re-mobilized during high-flow events.
Estuaries as fragmentation hotspots and transport regulators of microplastics
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Researchers combined field sampling across seasons with laboratory simulations in the Yangtze River Estuary to show that estuaries both fragment microplastics — shrinking average particle length by 7–31% along the land-to-sea gradient via turbidity zone abrasion — and regulate their transport, with concentrations roughly twice as high in inner versus offshore waters.
The dual role of coastal mangroves: Sinks and sources of microplastics in rapidly urbanizing areas
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Researchers studied microplastic dynamics in mangrove ecosystems along two rivers and a coastal mangrove park in China's Pearl River Estuary. They found that mangroves play a dual role, acting as both sinks that trap microplastics and sources that release them back into the environment. The study highlights that rapid urbanization significantly increases microplastic loads in these sensitive coastal ecosystems.
Exposing estuarine regions as microplastic traps: modeling transport pathways and accumulation hotspots in the Minho Estuary (Portugal-Spain)
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Researchers combined field sampling with a Lagrangian particle tracking model in the Minho Estuary to map how river discharge and tidal cycles control microplastic transport, identifying persistent accumulation hotspots and determining the conditions under which the estuary shifts between acting as a source versus a sink for ocean-bound microplastics.
Hydrology Modulates the Microplastics Composition and Transport Flux Across the River–Sea Interface in Zhanjiang Bay, China
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Researchers measured how tides and seasonal rainfall affect the movement of microplastics through an estuary in southern China. They found that microplastic levels rose during low tides and dropped during high tides, with an estimated 1.6 billion particles flowing from river to sea each year. The findings provide a framework for understanding how water flow patterns drive microplastic transport into coastal environments.
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When a large batch of papers lands in the Atlas, we read through it and send a short write-up of what stood out.