Modelling the conveyance of plastic pollution in rivers: Is storage within fluvial systems the key to the missing ocean plastic conundrum

概述：塑料污染环境是一个主要的全球问题，对野生动物、它们的栖息地和环境美学产生负面影响(Welden，2020)。河流被广泛认为是在陆地景观中转移废弃塑料废物的主要走廊。对全球河流流向海洋的估计范围为1.15-2.41(Lebreton等人，2017年)和0.41-4Mt yr-1(Schmidt等人，2017年)。然而，人们对塑料如何在河流系统中移动知之甚少。最近的研究表明，河流作为塑料运输的“急速传送带”，就像它们对沉积物的作用一样(Ferguson，1981)。例如，大型塑料(&gt；5 mm)可被植被和其他河道障碍物捕获(Schreyer等人，2021年；Newbould等人，2021年)，而微塑料(1 m-5 mm)和纳米塑料(&lt；1米)可累积并暂时储存在河道沉积物中(Hurley等人，2018年)。这表明，塑料垃圾在河流中的运输可以被概念化为临时储存地点之间的一系列离散的“台阶”，其动态将显示河流地貌和水力、集水水文、河岸植被和塑料特性(如大小、形态、浮力、密度、生物污染)之间复杂的相互依存关系。Newbould等人(2021)证明，可以用随机过程描述的捕捉点的搁浅和释放事件来模拟1公里范围内浮力巨型塑料垃圾的转移。该模型利用现场示踪剂数据进行了校准，并提供了一种潜在的方法来模拟塑料在河网中的传输，该模型明确地解释了不同类型塑料废物的传输行为。本研究的目的是开发、校准和测试更通用的塑料传输的概率集水尺度模型。这将增加我们对河流系统中塑料通量和储存的理解，从而改善对塑料行为的预测。归根结底，这种更好的理解可能是弥合塑料对环境的预测排放量与世界海洋塑料估计储量之间差距的关键(所谓的“塑料缺失”问题：Cózar等人，2014年；Weiss等人，2021年)。

Overview:Plastic pollution of the environment is a major global concern, generating negative impacts on wildlife, their habitats and environmental aesthetics (Welden, 2020). Rivers are widely recognised as major corridors for the transfer of discarded plastic waste within terrestrial landscapes. Estimates of the global riverine flux to oceans range from 1.15-2.41 (Lebreton et al., 2017) and 0.41-4 Mt yr-1 (Schmidt et al., 2017). Relatively little, however, is known about how plastic moves through river systems. Recent research suggests that rivers act as 'jerky conveyor belts' for plastic conveyance, just as they do for sediment (Ferguson, 1981). For example, macroplastics (> 5 mm) can be trapped by vegetation and other channel obstructions (Schreyer et al., 2021; Newbould et al., 2021) and micro- (1 m - 5 mm) and nano-plastics (< 1 m) can accumulate and be temporarily stored in channel bed sediments (Hurley et al., 2018). This suggests that the transport of plastic debris in rivers can be conceptualised as a series of discrete 'steps' between sites of temporary storage, the dynamics of which will exhibit complex interdependencies between river geomorphology and hydraulics, catchment hydrology, riparian vegetation, and plastic characteristics (e.g. size, morphology, buoyancy, density, biofouling). Newbould et al., (2021) demonstrated that the transfer of buoyant macroplastic litter through a 1 km reach can be modelled probabilistically with stranding and release events at trapping points described by a stochastic process. The model was calibrated using field tracer data and offers a potential approach for modelling plastic conveyance through river channel networks that explicitly accounts for the transport behaviours of different types of plastic waste.The aim of this study is to develop, calibrate and test a more general probabilistic catchment scale model of plastic conveyance. This will increase our understanding of plastic fluxes and stores in river systems leading to improved predictions of plastic behaviour. Ultimately, this improved understanding could be the key to closing the gap on the disparity between predicted emissions of plastics to the environment and the estimated stock of plastic in the world's oceans (the so-called "missing plastic" question: Cózar et al., 2014; Weiss et al., 2021).