Accumulation of plastic litter is accelerating worldwide. Rivers are a source of microplastic (i.e., particles <5 mm) to oceans, but few measurements of microplastic retention in rivers exist. We adapted spiraling metrics used to measure particulate organic matter transport to quantify microplastic deposition using an outdoor experimental stream. We conducted replicated pulse releases of three common microplastics: polypropylene pellets, polystyrene fragments, and acrylic fibers, repeating measurements using particles with and without biofilms. Depositional velocity (vdep; mm/s) patterns followed expectations based on density and biofilm ‘stickiness’, where vdep was highest for fragments, intermediate for fibers, and lowest for pellets, with biofilm colonization generally increasing vdep. Comparing microplastic vdep to values for natural particles (e.g., fine and coarse particulate organic matter) showed that particle diameter was positively related to vdep and negatively related to the ratio of vdep to settling velocity (i.e., sinking rate in standing water). Thus, microplastic vdep in rivers can be quantified with the same methods and follows the same patterns as natural particles. These data are the first measurements of microplastic deposition in rivers, and directly inform models of microplastic transport at the landscape scale, making a key contribution to research on the global ecology of plastic waste.
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机译：塑料垃圾的积累在世界范围内正在加速。河流是海洋中微塑性物质的来源（即<5 mm的颗粒），但是对河流中的微塑性滞留量的测量很少。我们调整了用于测量颗粒有机物传输的螺旋度量，以使用室外实验流来量化微塑性沉积。我们对三种常见的微塑料进行了重复脉冲释放：聚丙烯粒料，聚苯乙烯片段和丙烯酸纤维，使用有或没有生物膜的颗粒重复测量。沉积速度（vdep; mm / s）模式遵循基于密度和生物膜“粘性”的预期，其中碎片的vdep最高，纤维的中间度，粒料的最低，生物膜定殖通常会增加vdep。将微塑性vdep与天然颗粒（例如细颗粒有机物和粗颗粒有机物）的值进行比较，发现粒径与vdep正相关，而与vdep与沉降速度之比（即静水下沉率）负相关。因此，河流中的微塑性vdep可以使用与天然颗粒相同的方法进行定量，并遵循相同的模式。这些数据是河流中微塑性沉积物的首次测量，直接为景观尺度上的微塑性运输模型提供了信息，为全球塑料废物生态研究做出了重要贡献。
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