Organic carbon burial by river meandering partially offsets bank erosion carbon fluxes in a discontinuous permafrost floodplain
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Published:2022-05-10
Issue:3
Volume:10
Page:421-435
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ISSN:2196-632X
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Container-title:Earth Surface Dynamics
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language:en
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Short-container-title:Earth Surf. Dynam.
Author:
Douglas Madison M.ORCID, Li Gen K.ORCID, Fischer Woodward W., Rowland Joel C., Kemeny Preston C., West A. JoshuaORCID, Schwenk Jon, Piliouras Anastasia P., Chadwick Austin J., Lamb Michael P.
Abstract
Abstract. Arctic river systems erode permafrost in their banks and mobilize particulate organic carbon (OC). Meandering rivers can entrain particulate OC from permafrost many meters below the depth of annual thaw, potentially enabling the production of greenhouse gases. However, the amount and fate of permafrost OC that is mobilized by river erosion is uncertain. To constrain OC fluxes due to riverbank erosion and deposition, we collected
riverbank and floodplain sediment samples along the Koyukuk River, which
meanders through discontinuous permafrost in the Yukon River watershed,
Alaska, USA, with an average migration rate of 0.52 m yr−1. We measured sediment total OC (TOC) content, radiocarbon activity, water content, bulk density, grain size, and floodplain stratigraphy. Radiocarbon activity and TOC content were higher in samples dominated by silt as compared to sand, which we used to map OC content onto floodplain stratigraphy and estimate carbon fluxes due to river meandering. Results showed that the Koyukuk River erodes and re-deposits a substantial flux of OC each year due to its depth and high migration rate, generating a combined OC flux of a similar magnitude to the floodplain net ecological productivity. However, sediment being eroded from cutbanks and deposited as point bars had similar OC stocks (mean ± 1 SD of 125.3±13.1 kg OC m−2 in cutbanks versus 114.0±15.7 kg OC m−2 in point bars) whether or not the banks
contained permafrost. We also observed radiocarbon-depleted biospheric OC in both cutbanks and permafrost-free point bars. These results indicate that a substantial fraction of aged biospheric OC that is liberated from
floodplains by bank erosion is subsequently re-deposited in point bars rather than being oxidized. The process of aging, erosion, and re-deposition of floodplain organic material may be intrinsic to river–floodplain dynamics, regardless of permafrost content.
Funder
National Defense Science and Engineering Graduate Hertz Foundation Biological and Environmental Research California Institute of Technology
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Geophysics
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