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Abstract Spatial heterogeneities in soil hydrology have been confirmed as a key control on CO2and CH4fluxes in the Arctic tundra ecosystem. In this study, we applied a mechanistic ecosystem model, CLM‐Microbe, to examine the microtopographic impacts on CO2and CH4fluxes across seven landscape types in Utqiaġvik, Alaska: trough, low‐centered polygon (LCP) center, LCP transition, LCP rim, high‐centered polygon (HCP) center, HCP transition, and HCP rim. We first validated the CLM‐Microbe model against static‐chamber measured CO2and CH4fluxes in 2013 for three landscape types: trough, LCP center, and LCP rim. Model application showed that low‐elevation and thus wetter landscape types (i.e., trough, transitions, and LCP center) had larger CH4emissions rates with greater seasonal variations than high‐elevation and drier landscape types (rims and HCP center). Sensitivity analysis indicated that substrate availability for methanogenesis (acetate, CO2 + H2) is the most important factor determining CH4emission, and vegetation physiological properties largely affect the net ecosystem carbon exchange and ecosystem respiration in Arctic tundra ecosystems. Modeled CH4emissions for different microtopographic features were upscaled to the eddy covariance (EC) domain with an area‐weighted approach before validation against EC‐measured CH4fluxes. The model underestimated the EC‐measured CH4flux by 20% and 25% at daily and hourly time steps, suggesting the importance of the time step in reporting CH4flux. The strong microtopographic impacts on CO2and CH4fluxes call for a model‐data integration framework for better understanding and predicting carbon flux in the highly heterogeneous Arctic landscape.
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Response of CO 2 and CH 4 emissions from Arctic tundra soils to a multifactorial manipulation of water table, temperature and thaw depth
Abstract Significant uncertainties persist concerning how Arctic soil tundra carbon emission responds to environmental changes. In this study, 24 cores were sampled from drier (high centre polygons and rims) and wetter (low centre polygons and troughs) permafrost tundra ecosystems. We examined how soil CO2and CH4fluxes responded to laboratory-based manipulations of soil temperature (and associated thaw depth) and water table depth, representing current and projected conditions in the Arctic. Similar soil CO2respiration rates occurred in both the drier and the wetter sites, suggesting that a significant proportion of soil CO2emission occurs via anaerobic respiration under water-saturated conditions in these Arctic tundra ecosystems. In the absence of vegetation, soil CO2respiration rates decreased sharply within the first 7 weeks of the experiment, while CH4emissions remained stable for the entire 26 weeks of the experiment. These patterns suggest that soil CO2emission is more related to plant input than CH4production and emission. The stable and substantial CH4emission observed over the entire course of the experiment suggests that temperature limitations, rather than labile carbon limitations, play a predominant role in CH4production in deeper soil layers. This is likely due to the presence of a substantial source of labile carbon in these carbon-rich soils. The small soil temperature difference (a median difference of 1 °C) and a more substantial thaw depth difference (a median difference of 6 cm) between the high and low temperature treatments resulted in a non-significant difference between soil CO2and CH4emissions. Although hydrology continued to be the primary factor influencing CH4emissions, these emissions remained low in the drier ecosystem, even with a water table at the surface. This result suggests the potential absence of a methanogenic microbial community in high-centre polygon and rim ecosystems. Overall, our results suggest that the temperature increases reported for these Arctic regions are not responsible for increases in carbon losses. Instead, it is the changes in hydrology that exert significant control over soil CO2and CH4emissions.
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- Award ID(s):
- 1932900
- PAR ID:
- 10474192
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Environmental Research: Ecology
- Volume:
- 2
- Issue:
- 4
- ISSN:
- 2752-664X
- Format(s):
- Medium: X Size: Article No. 045003
- Size(s):
- Article No. 045003
- Sponsoring Org:
- National Science Foundation
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