A Methodology to Characterize Riverine Macroplastic Emission Into the Ocean

Abstract

Land-based macroplastic is considered one of the major sources of marine plastic debris. However, estimations of plastic emission from rivers into the oceans remain scarce and uncertain, mainly due to a severe lack of standardized observations. To properly assess global plastic fluxes, detailed information on spatiotemporal variation in river plastic quantities and composition are urgently needed. In this paper, we present a new methodology to characterize riverine macroplastic dynamics. The proposed methodology was applied to estimate the plastic emission from the Saigon River, Vietnam. During a 2-week period, hourly cross-sectional profiles of plastic transport were made across the river width. Simultaneously, sub-hourly samples were taken to determine the weight, size and composition of riverine macroplastics (>5 cm). Finally, extrapolation of the observations based on available hydrological data yielded new estimates of daily, monthly and annual macroplastic emission into the ocean. Our results suggest that plastic emissions from the Saigon River are up to four times higher than previously estimated. Importantly, our flexible methodology can be adapted to local hydrological circumstances and data availability, thus enabling a consistent characterization of macroplastic dynamics in rivers worldwide. Such data will provide crucial knowledge for the optimization of future mediation and recycling efforts.

Plastic debris in rivers

“…Long‐term measurements on the Saigon river using visual counting revealed a strong seasonality of plastic transport and showed its distribution of the river width and length is strongly influenced by hydrometeorological factors such as wind, water level, and flow velocity (van Emmerik et al, ; van Emmerik, Strady et al, ). Other studies, such as the pan‐European RIMMEL project collected visual counting observations for over 40 rivers (González‐Fernández et al, ).…”

“…Similarly, for transport within rivers, fundamental research can shed additional light on what determines the transport rates, likelihood of entrapment or degradation rates of plastic debris. Available analyses show contradicting relations between river discharge and plastic concentrations (van Emmerik et al, ; Wagner et al, ). In some cases, increased discharge does not mobilize additional plastic (van Emmerik et al, ).…”

“…Once entered a river (see Figures 2 and 3), plastic transport is influenced by hydrological factors such as water level, flow velocity, and discharge (van Emmerik et al, 2018). Several studies found a positive correlation between river discharge and plastic transport (Castro-Jiménez et al, 2019;Moore et al, 2011).…”

“…However, most estimates range between 16 and 119 tonnes/year (Seine, Rhine, Po) (Gasperi et al, 2014;van der Wal et al, 2015). In Southeast Asia, estimates range between 2.1Á10 3 tonnes/year for the Jakarta waterways ( van Emmerik, Loozen et al, 2019) to 1.3Á10 3 tonnes/year for the Saigon river (van Emmerik et al, 2018;van Emmerik, Strady et al, 2019). This shows that river plastic emission may be a more distributed problem than previously assumed (Schmidt et al, 2017) as also urban drainage systems and smaller rivers emit several orders of magnitude more plastic than large rivers.…”

Riverine plastic emission from Jakarta into the ocean

“…The origin and fate of land-based plastic waste remains understudied, but riverine plastic pollution is an emerging field. In recent years, several studies have quantified plastic pollution in rivers, such as the river Seine (Gasperi et al 2014), the Thames (Morritt et al 2014), rivers in the Los Angeles area (Moore et al 2011) and the Saigon river (Lahens et al 2018, van Emmerik et al 2018. However, most studies tend to be biased towards European and North American rivers, as almost 70% of the riverine plastic studies have been done in highincome countries (Blettler et al 2018).…”