Coal fly ash is a major carbon flux in the Chang Jiang (Yangtze River) basin
Abstract
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.
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 https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1921544118/-/DCSupplemental.Attached Files
Published - e1921544118.full.pdf
Supplemental Material - pnas.1921544118.sapp.pdf
Supplemental Material - pnas.1921544118.sd01.xlsx
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Additional details
- PMCID
- PMC8166106
- Eprint ID
- 109188
- Resolver ID
- CaltechAUTHORS:20210519-141319478
- National Key Research and Development Program of China
- 2017YFD0800300
- Foster and Coco Stanback
- Terrestrial Hazard Observation and Reporting Center
- Resnick Sustainability Institute
- Created
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2021-05-21Created from EPrint's datestamp field
- Updated
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2023-07-17Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences, Resnick Sustainability Institute