Climate change is affecting the Arctic at an unprecedented rate, potentially releasing substantial amounts of greenhouse gases (CO2 (carbon dioxide) and CH4 (Methane)) from tundra ecosystems. Measuring greenhouse gas emissions in the Arctic, particularly outside of the summer period, is very challenging due to extreme weather conditions. This research project provided the first annual balance of both CH4 and CO2 fluxes in a total of five sites spanning a 300Km transect across the North Slope of Alaska (three sites in Barrow, one site in Aquasuk, and one site in Ivotuk). The results from the continuous year-round CH4 fluxes across these sites showed how cumulative emissions for the cold season accounted on average for 50% of the annual budget (Zona et al., 2016), a notably higher contribution than previously modelled, and also higher than observed in boreal Alaska. The analysis of the cold period CH4 fluxes suggested that the presence of an unfrozen soil layer in the fall and early winter was a major control on cold season CH4 emissions (Zona et al., 2016). We also cross-compared all instruments measuring ecosystem scale CO2 and CH4 fluxes operating at our sites, which allowed us to make recommendation of the best performing instruments under these extreme weather conditions. The best performing instruments were closed path analyzers and intermittently heated sonic anemometers which had the highest final data cover. A continuously heated anemometer increased data coverage relative to non-heated anemometers, but resulted in an overestimation of the fluxes (Goodrich et al., 2016). We developed an intermittent heating strategy that was only activated when the data quality was low, and appeared to be the preferable method to prevent icing while avoiding biases to the measurements. Closed and open-path analyzers showed good agreement, but data coverage was much greater when using closed-path analyzers, especially during winter (Goodrich et al., 2016). Given the importance of vegetation on greenhouse gas emissions, we also investigated the role of different vegetation types under a broad range of environmental conditions on the CH4 emissions. We found that vegetation type can be a very useful tool to describe the spatial variability in CH4 emissions over the landscape (McEwing et al., 2015), and that just two vegetation types were able to explain about 50% of the variability in CH4 fluxes across ecosystems even hundreds of kilometers apart (Davidson et al., 2016a). To upscale these plot scale fluxes we completed high resolution vegetation maps in each of our tower sites (Davidson et al., 2016b), which are the finest resolution maps currently available from these sites, and also contributed to larger scale mapping effort (Walker et al., 2016). The soil microbial analysis from soil cores collected across our sites showed an association between overall microbial diversity and latitude, with a higher diversity found in the northerly site and lower diversity in the southerly site, contrary to current knowledge (Wagner et al., accepted). We also measured CH4 and CO2 concentrations in the soil, which showed to be orders of magnitude higher than in the atmosphere (Arndt et al., 2016). Our results contributed to model development (Xu et al., 2016; Kobayashi et al., 2016; Liljedahl et al., 2016; Luus et al., 2017), and to a wide variety of other projects as shown by the hundreds of download of our data from Ameriflux. Overall, this grant resulted in the publication of 25 peer reviewed journal articles, including in high impact factor journals such as PNAS (Proceedings of the National Academy of Sciences of the United States of America), and Nature Climate Change, in addition to five more in review and in preparation, and supported the research of seven PhD students, two master students, and ten undergraduate students.
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Trace gas fluxes from tidal salt marsh soils: implications for carbon–sulfur biogeochemistry
Abstract. Tidal salt marsh soils can be a dynamic source of greenhouse gases such ascarbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O),as well as sulfur-based trace gases such as carbon disulfide (CS2) anddimethylsulfide (DMS) which play roles in global climate and carbon–sulfurbiogeochemistry. Due to the difficulty in measuring trace gases in coastalecosystems (e.g., flooding, salinity), our current understanding is based onsnapshot instantaneous measurements (e.g., performed during daytime lowtide) which complicates our ability to assess the role of these ecosystemsfor natural climate solutions. We performed continuous, automatedmeasurements of soil trace gas fluxes throughout the growing season toobtain high-temporal frequency data and to provide insights into magnitudesand temporal variability across rapidly changing conditions such as tidalcycles. We found that soil CO2 fluxes did not show a consistent dielpattern, CH4, N2O, and CS2 fluxes were highly variable withfrequent pulse emissions (> 2500 %, > 10 000 %,and > 4500 % change, respectively), and DMS fluxes onlyoccurred midday with changes > 185 000 %. When we comparedcontinuous measurements with discrete temporal measurements (during daytime,at low tide), discrete measurements of soil CO2 fluxes were comparablewith those from continuous measurements but misrepresent the temporalvariability and magnitudes of CH4, N2O, DMS, and CS2.Discrepancies between the continuous and discrete measurement data result indifferences for calculating the sustained global warming potential (SGWP),mainly by an overestimation of CH4 fluxes when using discretemeasurements. The high temporal variability of trace gas fluxes complicatesthe accurate calculation of budgets for use in blue carbon accounting andearth system models.
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- Award ID(s):
- 1652594
- NSF-PAR ID:
- 10395719
- Date Published:
- Journal Name:
- Biogeosciences
- Volume:
- 19
- Issue:
- 19
- ISSN:
- 1726-4189
- Page Range / eLocation ID:
- 4655 to 4670
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/bg-19-4655-2022
