You have full access to this open access article. As the largest individual contributor of freshwater inflow to the basin, the Rhone River is likely to be one of the main sources of microplastics MPs to the Mediterranean Sea.
In order to predict the fate of MPs discharged by the Rhone River, an innovative 3D Lagrangian dispersion of its particles associated with vertical velocities was modeled in Mediterranean ocean currents. Through winter and summer scenarios, the seasonal variability of transfers and the corresponding accumulation areas were depicted in the Northwestern Basin according to hydrodynamic conditions on the continental shelf of the Gulf of Lion and to the frontal dynamics from the Pyrenees to the North Balearic fronts.
Our results indicated that MP transfers were driven by mesoscale and sub-mesoscale structures, resulting in steep concentration gradients across fronts during summer, while winter energetic mixing favored a more efficient and homogeneous spreading. We estimated that 3. Seasonal distribution of floating and sinking MPs discharged by the Rhone River into the surface and bottom layers of the Mediterranean Sea.
Large quantities of mismanaged plastics are trapped and stored on continental surfaces Schwarz et al. Rivers therefore play an important role in marine contamination. Most of the plastic in numbers entering the sea are in the form of microplastics MPs Strokal et al. Distinction was made between primary MPs, purposefully manufactured in small size micro-beads used in cosmetics, fibers, industrial pellets , and secondary MPs that result from weathering and breakdown of larger plastic items.
Riverbanks are the place of intense transformation of macro debris into secondary MPs during their very slow transfer with transit times up to several decades before reaching the marine environment Tramoy et al. Previous modeling studies on river discharges of MPs to the ocean all highlighted the outstanding role of the Asian, south American, or African rivers as terrestrial sources Meijer et al. However, very recently Weiss et al. The hydrodynamics on the continental shelf is mainly influenced by two dominant winds, the Mistral at the eastern side and the Tramontane at the western side, by the inputs of the Rhone River and by the Northern Current Millot flowing along the continental slope.
