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

塑料对环境的污染是一个主要的全球性问题，对野生动物、它们的栖息地和环境美学产生负面影响（韦尔登，2020）。河流被广泛认为是陆地景观中废弃塑料废物转移的主要通道。全球河流流入海洋的流量估计值为1.15-2.41（Lebreton等人，2017）和0.41-4 Mt yr-1（施密特等人，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，河流就像塑料运输的“不稳定的传送带”，就像它们对沉积物所做的那样（Ferguson，1981）。例如，大塑料（> 5 mm）可以被植被和其他通道障碍物捕获（Schreyer等人，2021; Newbould等人，2021），并且微塑料（1 m - 5 mm）和纳米塑料（< 1 m）可以积累并暂时储存在河床沉积物中（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一系列离散的“步骤”之间的网站的临时存储，其动态将表现出复杂的相互依赖性河流地貌和水力学，流域水文，河岸植被和塑料特性（如大小，形态，浮力，密度，生物污损）。Newbould等人，（2021）表明，通过1 km河段的漂浮宏观塑料垃圾的转移可以通过随机过程描述的捕获点处的搁浅和释放事件进行概率建模。该模型使用现场示踪剂数据进行了校准，并提供了一个潜在的方法来模拟塑料输送通过河道网络，明确占不同类型的塑料waste.The研究的目的是运输behaviorsof开发，校准和测试一个更一般的概率流域尺度模型的塑料输送。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。最终，这种更好的理解可能是缩小预测的塑料排放量与世界海洋中估计的塑料存量之间差距的差距的关键（所谓的“失踪塑料”问题：Cózar等人，2014;韦斯等人，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).