Hydrology as a Driver of Floating River Plastic Transport

Abstract

Plastic pollution in aquatic ecosystems is a growing threat to ecosystem health and human livelihood. Recent studies show that the majority of environmental plastics accumulate within river systems for years, decades and potentially even longer. Long‐term and system‐scale observations are key to improve the understanding of transport and retention dynamics, to identify sources and sinks, and to assess potential risks. The goal of this study was to quantify and explain the variation in floating plastic transport in the Rhine‐Meuse delta, using a novel 1‐year observational data set. We found a strong positive correlations between floating plastic transport and discharge. During peak discharge events, plastic transport was found up to six times higher than under normal conditions. Plastic transport varied up to a factor four along the Rhine and Meuse rivers, which is hypothesized to be related to the complex river network, locations of urban areas, and tidal dynamics. Altogether, our findings demonstrate the important role of hydrology as driving force of plastic transport dynamics. Our study emphasizes the need for exploring other factors that may explain the spatiotemporal variation in floating plastic transport. The world's most polluted rivers are connected to the ocean through complex deltas. Providing reliable observations and data‐driven insights in the transport and dynamics are key to optimize plastic pollution prevention and reduction strategies. With our paper we aim to contribute to both advancing the fundamental understanding of plastic transport dynamics, and the establishment of long‐term and harmonized data collection at the river basin scale.

Urban water systems as entry points for river plastic pollution

“…Even though this estimate is based on reliable observations, the current impacts of potential drivers on transport and retention of litter is poorly understood. While environmental factors, such as (high intensity) rainfall events in urban areas could be drivers of litter transport to rivers [42], it is argued that these factors on its own cannot fully explain observed litter fluxes [34]. The low correlation values between precipitation, sunlight, wind speed, tidal regimes and observed item fluxes in our study confirm the latter.…”

“…Future research should explore additional monitoring techniques to quantify litter outflow. Since the relation between floating plastics and total plastics in the water column is unclear [42], the estimation of total outflow quantities based on just floating plastics could be inaccurate. Current technologies are either labour intensive and require heavy equipment [7,31] or are based on rudimentary techniques, such as acoustic sonar [9,15].…”

“…The floating litter flux F outlet for each outlet was calculated using the following formula, adapted from van Emmerik et al [42]:…”

“…High anthropogenic activity including recreation, open air markets, and tourism [11,26] are assumed to be the main causes for macrolitter leakage in urban water systems. Subsequent transport to riverine and marine environments is facilitated by (extreme) rainfall events and stormwater overflow [1], hydrologic conditions [42], and other environmental factors [33]. However, a lack of observational data prevents further exploration of the abundance, transport and retention dynamics in urban water systems.…”

“…Improving this understanding is critical, since many rivers are directly connected to urban water systems, which are often seen as main input locations for plastic litter (e.g. Rotterdam (Rhine) [42] , Ho Chi Minh City (Saigon) [23], Paris (Seine) [40,41], Barcelona (LLobregat & Besòs) [34], Jakarta (Ciliwung) This paper studies the emissions of floating litter from urban water systems and its relation to riverine plastic pollution for the water system of Amsterdam. This system is characterised by a dense network of urban canals directly connected to the IJ river, from which 42 metric tonnes of floating plastic is removed annually [48].…”