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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Response of vegetation and carbon fluxes to brown lemming herbivory in northern Alaska
Abstract. The warming of the Arctic is affecting the carbon cycle of tundraecosystems. Most research on carbon fluxes from Arctic tundra ecosystems hasfocused on abiotic environmental controls (e.g., temperature, rainfall, orradiation). However, Arctic tundra vegetation, and therefore the carbonbalance of these ecosystems, can be substantially impacted by herbivory. Inthis study we tested how vegetation consumption by brown lemmings (Lemmus trimucronatus) canimpact carbon exchange of a wet-sedge tundra ecosystem near Utqiaġvik,Alaska during the summer and the recovery of vegetation during the followingsummer. We placed brown lemmings in individual enclosure plots and testedthe impact of lemmings' herbivory on carbon dioxide (CO2) fluxes, methane(CH4) fluxes, and the normalized difference vegetation index (NDVI)immediately after lemming removal and during the following growing season.During the first summer of the experiment, lemmings' herbivory reduced plantbiomass (as shown by the decrease in the NDVI) and decreased net CO2uptake while not significantly impacting CH4 emissions. CH4emissions were likely not significantly affected due to CH4 beingproduced deeper in the soil and escaping from the stem bases of the vascularplants. The summer following the lemming treatments, NDVI and net CO2fluxes returned to magnitudes similar to those observed before the start ofthe experiment, suggesting a complete recovery of the vegetation and atransitory nature of the impact of lemming herbivory. Overall, lemmingherbivory has short-term but substantial effects on carbon sequestration byvegetation and might contribute to the considerable interannual variabilityin CO2 fluxes from tundra ecosystems.
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- Award ID(s):
- 1932900
- NSF-PAR ID:
- 10332550
- Date Published:
- Journal Name:
- Biogeosciences
- Volume:
- 19
- Issue:
- 11
- ISSN:
- 1726-4189
- Page Range / eLocation ID:
- 2779 to 2794
- 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-19-2779-2022
