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Particle clustering and dispersion in multi-scale Langmuir turbulence and regional flow convergence
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Researchers studied how ocean currents and wind-driven waves move harmful particles like microplastics through estuaries (where rivers meet the ocean), finding that these forces create narrow bands where pollution concentrates. Understanding how pollutants cluster in these specific areas matters because it helps scientists predict where people and wildlife are most exposed to dangerous microplastics and other contaminants in coastal waters.
Concentrations of pollutants, such as microplastics, can be used to predict exposure and assess risk to organisms. In estuaries, the clustering and dispersion of materials is influenced by flows ranging from small-scale wind, wave, and tidal turbulence to regional-scale circulations. Axial convergence, paired regional-scale roll cells formed via cross-estuary density gradients from tidal jets in channel estuaries, collect surface particles in convergent bands over length scales of O(100 m-10 km). Turbulent roll cells, such as Langmuir cells, instead collect surface and bottom particles over scales of O(10-100 m). Here, the dispersion and clustering of suspended particles along-estuary and cross-estuary in an estuary with multi-scale turbulent-axial convergent flow is examined to diagnose the combined influence on particle concentrations and pollution risks. A turbulence-resolving shallow-water large eddy simulation is modified with cross-estuary varying tidal flow and along-estuary density gradients to drive axial roll cells. Wind stress and Stokes drift drive shear and Langmuir turbulence (LT). In axially converging estuaries, tidal jet shear dominates particle dispersion, acting most efficiently among neutrally buoyant particles; dispersion of buoyantly rising particles is enhanced by vertical mixing from LT. With LT, particle clouds show increased clustering compared to model runs without LT, dividing into more numerous, narrower, yet denser band-like clusters within windrows. Langmuir turbulence during slack tides alters the regional dispersion and clustering of particles by axial convergence.
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Langmuir turbulence in a depth-varying coastal channel: Insights from large eddy simulations
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Scientists studied how ocean waves create spinning water currents in coastal areas like bays and rivers, which help mix pollution and tiny plastic particles throughout the water. These wave-driven currents are much stronger than previously thought and significantly change how pollutants like microplastics spread through coastal waters where people swim, fish, and get drinking water. Understanding these mixing patterns is important for predicting where ocean pollution ends up and how it might affect human health.
Clustering of particles in weakly divergent flows
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Ocean currents don't just spread out tiny particles like microplastics evenly—they actually cause them to clump together into clusters, similar to how debris gathers in swirling bathwater. This research develops math models to predict exactly how and where this clustering happens, whether particles are drifting with the current or floating on the surface, which matters because clustered microplastics are more likely to be eaten by marine life and could concentrate pollutants in specific ocean "hotspots" rather than being harmlessly diluted. Understanding these clustering patterns could eventually help scientists better predict where microplastic pollution accumulates and how it enters the food
The Role of Estuarine Axial Convergent Fronts in Microplastic Dispersal
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Researchers used a validated Delft3D hydrodynamic model coupled with Lagrangian particle tracking to show that axial convergent fronts in the Conwy estuary trap microplastics as an additional retention mechanism, but that high river-flow events disrupt these fronts and flush particles offshore—highlighting that estuarine microplastic fate depends on dynamic interplay between tidal and riverine forcing.
Study on the Mass Concentration Distributions of Marine Microplastics in Estuaries and Coastal Areas
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Researchers characterized the mass concentration distribution of marine microplastics in estuarine and coastal environments, measuring spatial gradients between river mouths and open coastal waters and identifying estuaries as major transition zones for microplastic flux.
Physical drivers of transport, dispersion and trapping of microplastics in a macrotidal, hyper-turbid fluvial–estuarine system: A modelling approach
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Estuaries — where rivers meet the ocean — act like traps for microplastics, with tides, sediment, and shoreline interactions causing much of this plastic pollution to get stuck rather than flushed out to sea. This matters because these are often the same waters used for fishing and shellfish harvesting, meaning trapped microplastics may build up in local food sources over time rather than dispersing and diluting in the open ocean.
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