Plastic in the environment is considered an emerging pollutant of global concern. In spite of intensive research, many questions remain open, such as the processes that drive the deposition and remobilization of plastic debris on river beaches. The objectives of this study were: i) to analyze the influence of the natural hydrological fluctuations and wind intensity on the distribution of mesoplastic (0.5–2.5 cm) and macroplastic (>2.5 cm) debris in beach sediments of a large river, ii) to describe the type of plastic debris found and iii) to explore potential relations between the number of items and weight of macro- and mesoplastics.

Our results suggest that, during lowering water levels, flow removes the plastic debris and transports it further downstream. Conversely, when the beach sediments remain exposed during long periods, the plastic debris accumulates considerably. Nevertheless, the influence of wind intensity on plastic debris transport was comparatively negligible. In other words, in our study the water flow had a greater capacity to remobilize and transport plastic debris than the wind.

The most abundant mesoplastic items were foam, hard plastic, film and small fragments of fishing line. The dominant macroplastic items recorded were pieces of fishing line (nylon) and cigarette filters (cellulose acetate), typically discarded by beach users. Other items found in large quantities were soft packaging elements (expanded polystyrene), hard plastic containers (polystyrene, polyethylene terephthalate) and beverage bottles (polyethylene terephthalate), typical items of domestic use in the Paraná River region.

Finally, we found that the density of macroplastic items is highly correlated to the density of mesoplastic items, serving as surrogate for further estimations. Our results could help to develop better mitigation strategies in seasonal riverscapes, based on the influence of the hydrological cycle and the characteristics of the most abundant meso- and macroplastics.

环境中的塑料被认为是全球关注的新兴污染物。尽管进行了深入研究，但仍有许多问题悬而未决，例如推动河滩上塑料碎片沉积和再流动的过程。本研究的目的是：i) 分析自然水文波动和风力强度对大河滩沉积物中中塑性 (0.5-2.5 cm) 和大塑性 (>2.5 cm) 碎片分布的影响，ii)描述发现的塑料碎片的类型和 iii) 探索物品数量与宏观和中塑料的重量之间的潜在关系。

我们的结果表明，在降低水位的过程中，水流会去除塑料碎片并将其输送到更远的下游。相反，当海滩沉积物长时间暴露在外时，塑料碎片会大量积聚。然而，风强度对塑料碎片运输的影响相对可以忽略不计。换句话说，在我们的研究中，水流比风具有更大的再动员和运输塑料碎片的能力。

最丰富的中塑料制品是泡沫、硬塑料、薄膜和钓鱼线的小碎片。记录的主要大塑料物品是钓鱼线（尼龙）和香烟过滤嘴（醋酸纤维素），通常由海滩使用者丢弃。其他大量发现的物品包括软包装元件（发泡聚苯乙烯）、硬塑料容器（聚苯乙烯、聚对苯二甲酸乙二醇酯）和饮料瓶（聚对苯二甲酸乙二醇酯），这是巴拉那河地区典型的家用物品。

最后，我们发现大塑料物品的密度与中塑料物品的密度高度相关，可作为进一步估计的替代品。基于水文循环的影响以及最丰富的中塑料和大塑料的特征，我们的研究结果有助于在季节性河流景观中制定更好的缓解策略。