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Coal fly ash is a major carbon flux in the Chang Jiang (Yangtze River) basin

Li, Gen K. and Fischer, Woodward W. and Lamb, Michael P. and West, A. Joshua and Zhang, Ting and Galy, Valier and Wang, Xingchen Tony and Li, Shilei and Qiu, Hongrui and Li, Gaojun and Zhao, Liang and Chen, Jun and Ji, Junfeng (2021) Coal fly ash is a major carbon flux in the Chang Jiang (Yangtze River) basin. Proceedings of the National Academy of Sciences of the United States of America, 118 (21). Art. No. e1921544118. ISSN 0027-8424. PMCID PMC8166106. doi:10.1073/pnas.1921544118.

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Fly ash—the residuum of coal burning—contains a considerable amount of fossilized particulate organic carbon (FOC_(ash)) that remains after high-temperature combustion. Fly ash leaks into natural environments and participates in the contemporary carbon cycle, but its reactivity and flux remained poorly understood. We characterized FOC_(ash) in the Chang Jiang (Yangtze River) basin, China, and quantified the riverine FOC_(ash) fluxes. Using Raman spectral analysis, ramped pyrolysis oxidation, and chemical oxidation, we found that FOC_(ash) is highly recalcitrant and unreactive, whereas shale-derived FOC (FOC_(rock)) was much more labile and easily oxidized. By combining mass balance calculations and other estimates of fly ash input to rivers, we estimated that the flux of FOCash carried by the Chang Jiang was 0.21 to 0.42 Mt C⋅y⁻¹ in 2007 to 2008—an amount equivalent to 37 to 72% of the total riverine FOC export. We attributed such high flux to the combination of increasing coal combustion that enhances FOCash production and the massive construction of dams in the basin that reduces the flux of FOC_(rock) eroded from upstream mountainous areas. Using global ash data, a first-order estimate suggests that FOC_(ash) makes up to 16% of the present-day global riverine FOC flux to the oceans. This reflects a substantial impact of anthropogenic activities on the fluxes and burial of fossil organic carbon that has been made less reactive than the rocks from which it was derived.

Item Type:Article
Related URLs:
URLURL TypeDescription CentralArticle Information
Li, Gen K.0000-0002-6300-3570
Fischer, Woodward W.0000-0002-8836-3054
Lamb, Michael P.0000-0002-5701-0504
West, A. Joshua0000-0001-6909-1471
Galy, Valier0000-0003-0385-8443
Wang, Xingchen Tony0000-0001-5316-789X
Li, Shilei0000-0001-7053-2828
Qiu, Hongrui0000-0002-4219-0039
Li, Gaojun0000-0002-2463-0774
Chen, Jun0000-0002-3480-5961
Additional Information:© 2021 Published under the PNAS license. Edited by Donald E. Canfield, University of Southern Denmark, Odense M., Denmark, and approved March 25, 2021 (received for review December 9, 2019) This project was funded by the National Key R&D Program of China (Grant 2017YFD0800300). G.K.L. acknowledges support from a California Institute of Technology Geology Option Postdoctoral Fellowship and a National Ocean Sciences Accelerator Mass Spectrometry Laboratory Graduate Intern Fellowship. W.W.F. and M.P.L. acknowledge support from Foster and Coco Stanback, California Institute of Technology’s Terrestrial Hazard Observation and Reporting Center, and the Resnick Sustainability Institute. We thank Yuliang Chen for help with data compilation. Data Availability. All study data are included in the article and/or supporting information. Author contributions: G.K.L., W.W.F., M.P.L., A.J.W., J.C., and J.J. designed research; G.K.L., T.Z., X.T.W., and S.L. performed research; G.K.L., T.Z., V.G., and J.J. contributed new reagents/analytic tools; G.K.L., W.W.F., M.P.L., V.G., X.T.W., S.L., H.Q., G.L., L.Z., and J.J. analyzed data; and G.K.L., W.W.F., M.P.L., A.J.W., T.Z., V.G., X.T.W., S.L., G.L., L.Z., J.C., and J.J. wrote the paper. The authors declare no competing interest. This article is a PNAS Direct Submission. This article contains supporting information online at
Group:Resnick Sustainability Institute
Funding AgencyGrant Number
National Key Research and Development Program of China2017YFD0800300
Foster and Coco StanbackUNSPECIFIED
Terrestrial Hazard Observation and Reporting CenterUNSPECIFIED
Resnick Sustainability InstituteUNSPECIFIED
Issue or Number:21
PubMed Central ID:PMC8166106
Record Number:CaltechAUTHORS:20210519-141319478
Persistent URL:
Official Citation:Coal fly ash is a major carbon flux in the Chang Jiang (Yangtze River) basin Gen K. Li, Woodward W. Fischer, Michael P. Lamb, A. Joshua West, Ting Zhang, Valier Galy, Xingchen Tony Wang, Shilei Li, Hongrui Qiu, Gaojun Li, Liang Zhao, Jun Chen, Junfeng Ji Proceedings of the National Academy of Sciences May 2021, 118 (21) e1921544118; DOI: 10.1073/pnas.1921544118
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109188
Deposited By: George Porter
Deposited On:21 May 2021 14:09
Last Modified:08 Feb 2022 23:41

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