Microplastics Distribution in Riverine Side Bars: the Combined Effect of Wind and Current

Rivers are the main pathway for the transport of MP toward the ocean. However, knowledge about the processes that drive the deposition and mobilization of MP in river SB remains very limited. The objectives of this study were: i) to determine the combined influence of hydrometric fluctuations and wind intensity on MP (<5mm) distribution in temporarily exposed SB and, ii) to determine the characteristics of the MP debris to infer their origin, fate, and potential impact on biota (i.e., type, polymer composition, size, and color). Additionally, we determined the dominant type of suspended MP in the water column (nearby the sampling sites) to compare them with MP in SB. Both, hydrological fluctuations and wind intensity played a significant role in MP distribution. Our data suggest that during the falling limb of the hydrograph (i.e., decreasing discharge), MP particles transported by the flow would be deposited on temporarily exposed SB, accumulating in high densities (no wind influence at this stage). Conversely, when sediments remain exposed to drought during long periods, MP are mobilized and transported by the wind. During this stage, MP densities significantly decreased on SB. The MP density ranged from 298 to 386 items/kg of sediment. The most abundant MP items were fibers (more than 90%), followed by fragments, films and fiber-rolls. The most abundant polymer was polyethylene (PE), followed by polyethylene terephthalate (PET), and cellulose based materials (CEL). This study outlines MP’s dynamics in SB, which could help policymakers, scientists and stakeholders better monitor and mitigate plastics pollution.