Physiochemical Controls on the Horizontal Exchange of Blue Carbon Across the Salt Marsh-Tidal Channel Interface

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Author(s)Fettrow, Sean
Author(s)Jeppi, Virginia
Author(s)Wozniak, Andrew
Author(s)Vargas, Rodrigo
Author(s)Michael, Holly
Author(s)Seyfferth, Angelia L.
Date Accessioned2023-08-31T18:39:09Z
Date Available2023-08-31T18:39:09Z
Publication Date2023-06-06
DescriptionAn edited version of this paper was published by AGU. Published 2023 American Geophysical Union. Fettrow, S., Jeppi, V., Wozniak, A., Vargas, R., Michael, H., & Seyfferth, A. L. (2023). Physiochemical controls on the horizontal exchange of blue carbon across the salt marsh-tidal channel interface. Journal of Geophysical Research: Biogeosciences, 128, e2023JG007404. https://doi.org/10.1029/2023JG007404. To view the published open abstract, go to https://doi.org/10.1029/2023JG007404. This artible will be embargoed until 12/06/2023. © 2023. American Geophysical Union. All Rights Reserved. This article will be embargoed until 12/06/2023.
AbstractTidal channels are biogeochemical hotspots that horizontally exchange carbon (C) with marsh platforms, but the physiochemical drivers controlling these dynamics are poorly understood. We hypothesized that C-bearing iron (Fe) oxides precipitate and immobilize dissolved organic carbon (DOC) during ebb tide as the soils oxygenate, and dissolve into the porewater during flood tide, promoting transport to the channel. The hydraulic gradient physically controls how these solutes are horizontally exchanged across the marsh platform-tidal channel interface; we hypothesized that this gradient alters the concentration and source of C being exchanged. We further hypothesized that trace soil gases (i.e., CO2, CH4, dimethyl sulfide) are pushed out of the channel bank as the groundwater rises. To test these hypotheses, we measured porewater, surface water, and soil trace gases over two 24-hr monitoring campaigns (i.e., summer and spring) in a mesohaline tidal marsh. We found that Fe2+ and DOC were positively related during flood tide but not during ebb tide in spring when soils were more oxidized. This finding shows evidence for the formation and dissolution of C-bearing Fe oxides across a tidal cycle. In addition, the tidal channel contained significantly (p < 0.05) more terrestrial-like DOC when the hydraulic gradient was driving flow toward the channel. In comparison, the channel water was saltier and contained significantly (p < 0.05) more marine-like DOC when the hydraulic gradient reversed direction. Trace gas fluxes increased with rising groundwater levels, particularly dimethyl sulfide. These findings suggest multiple physiochemical mechanisms controlling the horizontal exchange of C at the marsh platform-tidal channel interface. Plain Language Summary Tidal salt marshes store large amounts of carbon belowground in soils, but there is also a significant amount of carbon flowing into and out of these ecosystems via tidal channels. We investigated the carbon flowing between the channel bank and surface water in a salt marsh in Delaware. We found that soil minerals (i.e., iron oxides) control the mobility of carbon as iron oxides retain carbon during ebb tides and release carbon during flood tides as the minerals dissolve. The gradient between the groundwater and surface water elevation (i.e., hydraulic gradient) controls the flow direction for dissolved carbon, altering the concentration and source of carbon found in the tidal channel across tidal cycles. In addition, gases trapped in channel banks are pushed out of the soils as the tide rises. These findings will improve our understanding of carbon cycles in these critical carbon sinks. Key Points - Physiochemical mechanisms control horizontal exchange of carbon across marsh-tidal channel interfaces, affecting lateral carbon flux - Dissolution and reprecipitation of carbon-bearing Fe oxides during flood and ebb tides control the horizontal mobility of carbon - Hydraulic gradients control the carbon character in the tidal channel, and rising tides push greenhouse gases out of the channel bank
SponsorWe thank UD Soil Testing Laboratory for analytical assistance and the staff of the Delaware National Estuarine Research Reserve (DNERR). S.F. acknowledges support from the Delaware Environmental Institute. R.V. acknowledges support from the National Science Foundation (Grant 1652594). A.L.S. and H.M. acknowledge support from the National Science Foundation (Grants 1759879 and 2012484). The authors acknowledge that the land on which they conducted this study is the traditional home of the Lenni-Lenape tribal nation (Delaware nation).
CitationFettrow, S., Jeppi, V., Wozniak, A., Vargas, R., Michael, H., & Seyfferth, A. L. (2023). Physiochemical controls on the horizontal exchange of blue carbon across the salt marsh-tidal channel interface. Journal of Geophysical Research: Biogeosciences, 128, e2023JG007404. https://doi.org/10.1029/2023JG007404
ISSN2169-8961
URLhttps://udspace.udel.edu/handle/19716/33282
Languageen_US
PublisherJournal of Geophysical Research: Biogeosciences
Keywordschromophoric dissolved organic carbon
Keywordshorizontal carbon flux
KeywordsFe oxides
Keywordssoil trace gas flux
Keywordslateral carbon flux
Keywordstidal salt marsh
TitlePhysiochemical Controls on the Horizontal Exchange of Blue Carbon Across the Salt Marsh-Tidal Channel Interface
TypeArticle
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