River plastic emissions to the world’s oceans

River plastic emissions to the world’s oceans Laurent Lebreton Joost van der Zwet Jan-Willem Damsteeg Boyan Slat Anthony L. Andrady Júlia Reisser

Tag layer of the DHSS Meta-Tagging Project. The article text is reproduced from the staged copy named in sourceDesc and is not altered; the tags are held separately in standOff so that overlapping and nested spans are preserved.

River plastic emissions to the world’s oceans 2017 Nature Communications 10.1038/ncomms15611 lebreton2017-river-plastic-emissions-to-the-wor lebreton2017-river-plastic-emissions-to-the-wor.txt, the project's staged copy 83d0fa0be6cf608f66f39e9943577a42fede78bd cc-by environmental-science

the paper's own words

the tag layer; a sentence written by the tagger about the paper, always anchored to a quotation but not itself a quotation

0 spans located by searching the stored text for the quote's exact words, allowing any whitespace between them the mass of plastic entering the ocean from rivers each year, and how it is distributed in space and across the seasons Quotation withheld because this record is not cleared for redistribution. how much plastic inland populations contribute to the ocean through rivers - a global figure that did not exist, where the coastal contribution already did Quotation withheld because this record is not cleared for redistribution. a global model of riverine plastic input calibrated against 30 field observations from 13 rivers, giving 1.15-2.41 million tonnes per year with its seasonality and its top contributors named Quotation withheld because this record is not cleared for redistribution. existence Quotation withheld because this record is not cleared for redistribution. a global flux nobody had measured, whose magnitude turns out to be set by waste management and monsoon rainfall in a handful of Asian catchments Quotation withheld because this record is not cleared for redistribution. computational-model computational-model Quotation withheld because this record is not cleared for redistribution. mismanaged waste sits on land until rainfall mobilises it; surface runoff both introduces new plastic to the river during heavy rain and remobilises deposited particles during floods, so input tracks the monsoon rather than the population runoff as the transport term Quotation withheld because this record is not cleared for redistribution. an artificial barrier intercepts surface plastic, so the load reaching the river mouth reflects only the catchment area downstream of the last dam - which is why moving that boundary changes the global total dams as accumulation sinks Quotation withheld because this record is not cleared for redistribution. one catchment with plastic concentrations orders of magnitude above every other sampled river dominates a regression across 30 points, so including it raises the correlation from 0.41 to 0.99 without the model having improved outlier leverage on a fitted correlation Quotation withheld because this record is not cleared for redistribution. the model rests on the assumption that dams intercept ALL plastic, which the authors name as a major assumption; 2.13-4.46 million tonnes per year is generated upstream of dams and simply not counted Quotation withheld because this record is not cleared for redistribution. there is very little data to document the assumptions about Asian contributions or to thoroughly verify the validity of the model - stated by the authors about the region that supplies 86% of their total Quotation withheld because this record is not cleared for redistribution. the estimate covers only the sampled size spectrum - nothing below the net mesh, nothing above the trawl aperture, nothing below the sampled depth - so it is conservative by construction Quotation withheld because this record is not cleared for redistribution. the global prediction doubles from the lower to the upper estimate once the extrapolation uncertainties in the calibration dataset are propagated Quotation withheld because this record is not cleared for redistribution. studies reporting only particle counts were converted to mass using a mean micro/macro ratio and mean particle masses measured AT SEA, not in rivers - an extrapolation the authors name as a limitation of the calibration Quotation withheld because this record is not cleared for redistribution. the hydrological model's discharge predictions are known to run dryer than observations across 66 basins, attributed to precipitation uncertainty Quotation withheld because this record is not cleared for redistribution. observed plastic concentrations differ by several orders of magnitude between sampled rivers, and sampling designs, devices and reported units vary substantially - so the calibration set is heterogeneous before any model is fitted Quotation withheld because this record is not cleared for redistribution. land-surface hydrology - the GLDAS/NOAH runoff model built for terrestrial water and energy budgets - carried into a plastic-transport estimate as the seasonality term Quotation withheld because this record is not cleared for redistribution. mean particle masses and the micro-to-macro ratio measured in the open ocean, carried into rivers to convert particle counts into mass where studies reported only counts Quotation withheld because this record is not cleared for redistribution. removing the Yangtze measurement as an outlier before testing the model-observation correlation, rather than reporting the flattering fit eliminates: a model-observation correlation carried by one extreme measurement · outcome: held Quotation withheld because this record is not cleared for redistribution. re-deriving the regression with mismanaged waste counted upstream of dams as well, to test whether the global answer depends on where a dam is treated as a sink eliminates: a global input figure that depends on whether a dam is treated as a sink · outcome: partial Quotation withheld because this record is not cleared for redistribution. choosing monthly rather than yearly averaged runoff, tested against the observed flux inputs instead of assumed eliminates: a runoff averaging window chosen because it fits, rather than because it predicts the observed flux · outcome: held Quotation withheld because this record is not cleared for redistribution. a sensitivity analysis over the micro/macro ratio and mean particle masses, using the ranges observed at sea eliminates: a mass estimate that holds only at one assumed micro-to-macro ratio and one assumed particle mass · outcome: partial Quotation withheld because this record is not cleared for redistribution. applying the same model to coastal populations, so the new estimate could be placed against the existing coastal one on its own terms eliminates: a river estimate and a coastal estimate that cannot be compared because they were produced by different models · outcome: held Quotation withheld because this record is not cleared for redistribution. the hydrological model's discharge predictions checked against observations in 66 basins worldwide eliminates: a plastic flux resting on modelled discharge that was never checked against a gauge · outcome: partial Quotation withheld because this record is not cleared for redistribution. mass balance mass balance Quotation withheld because this record is not cleared for redistribution. MPW MPW Quotation withheld because this record is not cleared for redistribution. artificial barriers artificial barriers Quotation withheld because this record is not cleared for redistribution. catchment runoff catchment runoff Quotation withheld because this record is not cleared for redistribution. buoyant plastics buoyant plastics Quotation withheld because this record is not cleared for redistribution. macro-plastic macro-plastic Quotation withheld because this record is not cleared for redistribution. Yangtze River Yangtze River Quotation withheld because this record is not cleared for redistribution. coastal populations coastal populations Quotation withheld because this record is not cleared for redistribution. sensitivity analysis sensitivity analysis Quotation withheld because this record is not cleared for redistribution. monthly averaged runoff monthly averaged runoff Quotation withheld because this record is not cleared for redistribution. model-observation correlation - WITH THE YANGTZE EXCLUDED as an outlier: r=0.4132, P<0.05, n=29. The value the paper uses Quotation withheld because this record is not cleared for redistribution. model-observation correlation - WITH THE YANGTZE INCLUDED: r=0.99, P<0.05, n=30, which the authors call much higher and biased. One data point separates the two Quotation withheld because this record is not cleared for redistribution. global river plastic input - COUNTING MISMANAGED WASTE DOWNSTREAM OF DAMS: 1.15-2.41 million tonnes per year. The published headline Quotation withheld because this record is not cleared for redistribution. global river plastic input - COUNTING WASTE UPSTREAM OF DAMS TOO: 0.76-1.55 million tonnes per year, midpoint 0.91. Same model, same data, a different decision about where a dam stops being a sink Quotation withheld because this record is not cleared for redistribution. extends → the global estimate of plastic entering the ocean from coastal populations (4.8-12.7 million tonnes per year), by adding the inland contribution transported by rivers Quotation withheld because this record is not cleared for redistribution. qualifies → direct comparison between riverine and coastal plastic input estimates, which measure different materials by different methods Quotation withheld because this record is not cleared for redistribution. critiques → the state of freshwater plastic monitoring - unstandardised methodologies, incompatible reported units, and particle counts published without masses Quotation withheld because this record is not cleared for redistribution. builds-on → the local river sampling studies from Europe, Asia and the Americas that supply the 30 calibration observations across 13 rivers Quotation withheld because this record is not cleared for redistribution. between 1.15 and 2.41 million tonnes of plastic enters the ocean from rivers each year, with the top 20 rivers accounting for 67% between 1.15 and 2.41 million tonnes of plastic enters the ocean from rivers each year, with the top 20 rivers accounting for 67% Quotation withheld because this record is not cleared for redistribution. the model-observation correlation is 0.41 without the Yangtze and 0.99 with it - the authors call the second biased and use the first the model-observation correlation is 0.41 without the Yangtze and 0.99 with it - the authors call the second biased and use the first Quotation withheld because this record is not cleared for redistribution. counting mismanaged waste upstream of dams as well gives 0.76-1.55 million tonnes per year from the same model and data counting mismanaged waste upstream of dams as well gives 0.76-1.55 million tonnes per year from the same model and data Quotation withheld because this record is not cleared for redistribution. more than 74.5% of the annual river plastic input occurs between May and October, driven by the East Asian monsoon more than 74.5% of the annual river plastic input occurs between May and October, driven by the East Asian monsoon Quotation withheld because this record is not cleared for redistribution. There is very little data to verify the model's assumption of a dominant contribution from Asian rivers. There is very little data to verify the model's assumption of a dominant contribution from Asian rivers. Quotation withheld because this record is not cleared for redistribution. at least 2.8-18.6% of coastal plastic emissions occur via river transport, with a further 0.79-1.52 million tonnes per year arriving from inland at least 2.8-18.6% of coastal plastic emissions occur via river transport, with a further 0.79-1.52 million tonnes per year arriving from inland Quotation withheld because this record is not cleared for redistribution. the ocean-plastic accounting exercise this estimate is offered as baseline data for - the reason the record joins to counts of plastic already at sea mass balance Quotation withheld because this record is not cleared for redistribution. dams and weirs, assumed by the model to act as sinks for all plastic particles - named by the authors as a major and conservative assumption artificial barriers Quotation withheld because this record is not cleared for redistribution. the headline annual river plastic input, counting mismanaged waste downstream of dams 1.15 and 2.41 million tonnes Quotation withheld because this record is not cleared for redistribution. the same model's answer when waste upstream of dams is counted too 0.76–1.55 million tonnes per year Quotation withheld because this record is not cleared for redistribution. the prior estimate of plastic entering the ocean from coastal populations 4.8 and 12.7 million tonnes Quotation withheld because this record is not cleared for redistribution. share of the global total from the top 20 polluting rivers 67% Quotation withheld because this record is not cleared for redistribution. share of the global total from Asian rivers 86% Quotation withheld because this record is not cleared for redistribution. share of freshwater plastic input the model treats as retained behind dams 65% Quotation withheld because this record is not cleared for redistribution. Pearson product-moment test Pearson product-moment test Quotation withheld because this record is not cleared for redistribution. r=0.4132 r=0.4132 Quotation withheld because this record is not cleared for redistribution. r=0.99 r=0.99 Quotation withheld because this record is not cleared for redistribution. MPW MPW Quotation withheld because this record is not cleared for redistribution. monthly averaged runoff monthly averaged runoff Quotation withheld because this record is not cleared for redistribution.

The full text of this article is not redistributable, so it is not included here. The evidence sentences are withheld with it; the tag layer and its grounding status remain. The article itself is at https://doi.org/10.1038/ncomms15611.