Rivers are the main pathway for microplastics (MP) transport toward the ocean. However, the understanding of the processes involved in the deposition and mobilization of MP in rivers, specifically in sediment side bars (SB), remains very limited. The objectives of this study were: (i) to examine the effect of hydrometric fluctuations and wind intensity on the distribution of microplastics (MP < 5 mm) in the SB of large river (the Paraná River), (ii) to determine the characteristics of MP to infer their origin and fate, and (iii) to discuss potential similarities or differences between MP suspended in the water column and MP found in sediment. The SB and water column were sampled during the autumn, winter, and spring of 2018, and the summer of 2019 at different river discharges and wind intensities. >90 % of the MP items found were fiber of polyethylene terephthalate (PET; FT-IR analysis), the most common MP color was blue, and most were in the 0.5–2 mm size range. The concentration/composition of MP varied according to the river discharge and wind intensity. During the falling limb of the hydrograph when discharge is decreasing and sediments are exposed for short periods (13–30 days), MP particles transported by the flow were deposited on temporarily exposed SB, accumulating there in high densities (309–373 items/kg). However, during the drought, when sediments remained exposed for a long time (259 days), MP were mobilized and transported by the wind. During this period (no influence of the flow), MP densities significantly decreased on SB (39–47 items/kg). In conclusion, both hydrological fluctuations and wind intensity played a significant role in MP distribution in SB.

河流是微塑料（MP）向海洋输送的主要途径。然而，对河流中 MP 的沉积和流动过程的了解，特别是在沉积物边坝 (SB) 中，仍然非常有限。本研究的目的是：(i) 研究水文波动和风强度对大河（巴拉那河）SB 中微塑料（MP < 5 毫米）分布的影响，(ii) 确定特征(iii) 讨论悬浮在水体中的 MP 与沉积物中发现的 MP 之间的潜在相似点或差异。SB和水柱是在2018年秋季、冬季和春季以及2019年夏季在不同河流流量和风力强度下采样的。发现的 MP 物品中 >90% 是聚对苯二甲酸乙二醇酯纤维（PET；FT-IR 分析），最常见的 MP 颜色为蓝色，大多数尺寸范围为 0.5–2 毫米。MP 的浓度/成分根据河流流量和风力强度而变化。在水文过程线的下降边缘期间，当流量减少且沉积物短时间（13-30天）暴露时，水流输送的MP颗粒沉积在暂时暴露的SB上，在那里以高密度积累（309-373个/kg） ）。然而，在干旱期间，当沉积物暴露时间较长（259天）时，MP被风动员和输送。在此期间（不受流量影响），SB 上的 MP 密度显着下降（39-47 个/kg）。总之，水文波动和风强对SB的MP分布起着重要作用。