Coastal salt marshes store large amounts of carbon but the magnitude and patterns of greenhouse gas (GHG; i.e., carbon dioxide (CO2) and methane (CH4)) fluxes are unclear. Information about GHG fluxes from these ecosystems comes from studies of sediments or at the ecosystem‐scale (eddy covariance) but fluxes from tidal creeks are unknown. We measured GHG concentrations in water, water quality, meteorological parameters, sediment CO2efflux, ecosystem‐scale GHG fluxes, and plant phenology; all at half‐hour intervals over 1 year. Manual creek GHG flux measurements were used to calculate gas transfer velocity (
Tidal salt marshes produce and emit CH4. Therefore, it is critical to understand the biogeochemical controls that regulate CH4spatial and temporal dynamics in wetlands. The prevailing paradigm assumes that acetoclastic methanogenesis is the dominant pathway for CH4production, and higher salinity concentrations inhibit CH4production in salt marshes. Recent evidence shows that CH4is produced within salt marshes via methylotrophic methanogenesis, a process not inhibited by sulfate reduction. To further explore this conundrum, we performed measurements of soil–atmosphere CH4and CO2fluxes coupled with depth profiles of soil CH4and CO2pore water gas concentrations, stable and radioisotopes, pore water chemistry, and microbial community composition to assess CH4production and fate within a temperate tidal salt marsh. We found unexpectedly high CH4concentrations up to 145,000 μmol mol−1positively correlated with S2−(salinity range: 6.6–14.5 ppt). Despite large CH4production within the soil, soil–atmosphere CH4fluxes were low but with higher emissions and extreme variability during plant senescence (84.3 ± 684.4 nmol m−2 s−1). CH4and CO2within the soil pore water were produced from young carbon, with most Δ14C‐CH4and Δ14C‐CO2values at or above modern. We found evidence that CH4within soils was produced by methylotrophic and hydrogenotrophic methanogenesis. Several pathways exist after CH4is produced, including diffusion into the atmosphere, CH4oxidation, and lateral export to adjacent tidal creeks; the latter being the most likely dominant flux. Our findings demonstrate that CH4production and fluxes are biogeochemically heterogeneous, with multiple processes and pathways that can co‐occur and vary in importance over the year. This study highlights the potential for high CH4production, the need to understand the underlying biogeochemical controls, and the challenges of evaluating CH4budgets and blue carbon in salt marshes.
more » « less- Award ID(s):
- 1652594
- NSF-PAR ID:
- 10478186
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 30
- Issue:
- 1
- ISSN:
- 1354-1013
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Coastal salt marshes store large amounts of carbon but the magnitude and patterns of greenhouse gas (GHG; i.e., carbon dioxide (CO2) and methane (CH4)) fluxes are unclear. Information about GHG fluxes from these ecosystems comes from studies of sediments or at the ecosystem-scale (eddy covariance) but fluxes from tidal creeks are unknown.more » « lessThis dataset includes GHG concentrations in water, water quality, meteorology, sediment CO2 efflux, ecosystem-scale GHG fluxes, and plant phenology; all at half-hour time-steps over one year.This study was carried out in the St. Jones Reserve, a component of the Delaware National Estuarine Research Reserve in Dover, Delaware, U.S.A. The study site is part of the following networks:- AmeriFlux (https://ameriflux.lbl.gov/sites/siteinfo/US-StJ)- Phenocam (https://phenocam.sr.unh.edu/webcam/sites/stjones/)The GHG concentration and efflux sampling point was located at Aspen Landing within a microtidal (mean tide range of 1.5 m), mesohaline (typical salinity of 5-18 ppt) salt marsh (Delaware Department of Natural Resources and Environmental Control, 2006) tidal creek.Main reference:
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