Geochemical Analysis of Permafrost Soils Reveals Factors Controlling Methane Emissions from Arctic Tundra

Summary

A recent study measured the changes in dissolved organic carbon compounds during anoxic incubations of low-centered polygon soils from the Barrow Environmental Observatory in Alaska (Herndon et al. 2015a). Analyses used Fourier transform infrared and ultraviolet-visible spectroscopies to identify an initial increase in soluble carbohydrate and organic acid pools, followed by a decline in organic acids. These results describe the upstream microbial processes of soil organic matter decomposition that feed anaerobic microbial fermentation, methanogenesis, and iron reduction, which are highly temperature-sensitive processes and thus likely to control rate and magnitude of methane emissions from thawing permafrost. In a companion study, samples from mineral and organic soils were analyzed at the Stanford Synchrotron Radiation Lightsource to further characterize the geochemistry of active layer soils and permafrost (Herndon et al. 2015b). From those results, the researchers infer that geochemical differences induced by water saturation dictate microbial products of soil organic matter decomposition, and that iron geochemistry is an important factor regulating methanogenesis in anoxic tundra soils. Together, these coordinated datasets provided a conceptual framework from which to parameterize and enhance fine-scale biogeochemical models from the Next-Generation Ecosystem Experiments-Arctic project that specifically represent these anaerobic processes. The datasets are being used to assess the effects of newly represented iron-reduction processes on simulations of carbon dioxide, methane, and pH production in one-dimensional models.

References

• Herndon, E. M., B. F. Mann, T. R. Chowdhury, Z. Yang, D. E. Graham, S. D. Wullschleger, L. Liang, and B. Gu. 2015a. “Pathways of Anaerobic Organic Matter Decomposition in Tundra Soils from Barrow, Alaska,” Journal of Geophysical Research Biogeosciences 120, 2345-59. DOI: 10.1002/2015JG003147.
• Herndon, E. M., Z. Yang, J. Bargar, N. Janot, T. Z. Regier, D. E. Graham, S. D. Wullschleger, B. Gu, and L. Liang. 2015b. “Geochemical Drivers of Organic Matter Decomposition in the Active Layer of Arctic Tundra Soils,” Biogeochemistry 126(3), 397-414. DOI: 10.1007/s10533-015-0165-5.