Deep Unsaturated Zone Contributions to Carbon Cycling in Semiarid Environments

Jiamin Wan; Tetsu K. Tokunaga; Wenming Dong; Kenneth H. Williams; Yongman Kim; Mark E. Conrad; Markus Bill; William J. Riley; Susan S. Hubbard

doi:10.1029/2018JG004669

Deep Unsaturated Zone Contributions to Carbon Cycling in Semiarid Environments

Jiamin Wan, Tetsu K. Tokunaga, Wenming Dong, Kenneth H. Williams, Yongman Kim, Mark E. Conrad, Markus Bill, William J. Riley, Susan S. Hubbard

Research output: Contribution to journal › Article › peer-review

18 Scopus citations

Abstract

Understanding terrestrial carbon cycling has relied primarily on studies of topsoils that are typically characterized to depths shallower than 0.5 m. At a semiarid site instrumented down to 7 m, we measured seasonal- and depth-resolved carbon inventories and fluxes and groundwater and unsaturated zone flow rates. Measurements showed that ~30% of the CO₂ efflux to the atmosphere (60% in winter) originates from below 1 m, contrary to predictions of less than 1% by Earth System Model land modules. Respiration from deeper roots and deeper microbial communities is supported by favorable subsurface temperatures, moisture, and oxygen availability. Below 1 m, dissolved organic carbon fluxes from the overlying soil and C from deep roots and exudates are expected to be important in sustaining microbial respiration. Because these conditions are characteristic of semiarid climate regions, we contend that Earth System Model land modules should incorporate such deeper soil processes to improve CO₂ flux predictions.

Original language	English
Pages (from-to)	3045-3054
Number of pages	10
Journal	Journal of Geophysical Research: Biogeosciences
Volume	123
Issue number	9
DOIs	https://doi.org/10.1029/2018JG004669
State	Published - Sep 2018
Externally published	Yes

Funding

This work was conducted as part of the Genomes to Watershed Scientific Focus Area at Lawrence Berkeley National Laboratory and was supported by the U.S. Department of Energy (DOE) Subsurface Biogeochemical Research Program, DOE Office of Science, Office of Biological and Environmental Research, under contract DE-AC02- 05CH11231. We thank the anonymous reviewers very much for their helpful comments.

Funders	Funder number
DOE Office of Science
Office of Biological and Environmental Research	DE-AC02- 05CH11231
U.S. Department of Energy

Keywords

DOC flux
ESM land modules
carbon cycling
carbon fluxes
deep unsaturated zone
semiarid environments

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10.1029/2018JG004669

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title = "Deep Unsaturated Zone Contributions to Carbon Cycling in Semiarid Environments",

abstract = "Understanding terrestrial carbon cycling has relied primarily on studies of topsoils that are typically characterized to depths shallower than 0.5 m. At a semiarid site instrumented down to 7 m, we measured seasonal- and depth-resolved carbon inventories and fluxes and groundwater and unsaturated zone flow rates. Measurements showed that ~30% of the CO2 efflux to the atmosphere (60% in winter) originates from below 1 m, contrary to predictions of less than 1% by Earth System Model land modules. Respiration from deeper roots and deeper microbial communities is supported by favorable subsurface temperatures, moisture, and oxygen availability. Below 1 m, dissolved organic carbon fluxes from the overlying soil and C from deep roots and exudates are expected to be important in sustaining microbial respiration. Because these conditions are characteristic of semiarid climate regions, we contend that Earth System Model land modules should incorporate such deeper soil processes to improve CO2 flux predictions.",

keywords = "DOC flux, ESM land modules, carbon cycling, carbon fluxes, deep unsaturated zone, semiarid environments",

author = "Jiamin Wan and Tokunaga, {Tetsu K.} and Wenming Dong and Williams, {Kenneth H.} and Yongman Kim and Conrad, {Mark E.} and Markus Bill and Riley, {William J.} and Hubbard, {Susan S.}",

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AU - Wan, Jiamin

AU - Tokunaga, Tetsu K.

AU - Dong, Wenming

AU - Williams, Kenneth H.

AU - Kim, Yongman

AU - Conrad, Mark E.

AU - Bill, Markus

AU - Riley, William J.

AU - Hubbard, Susan S.

PY - 2018/9

Y1 - 2018/9

N2 - Understanding terrestrial carbon cycling has relied primarily on studies of topsoils that are typically characterized to depths shallower than 0.5 m. At a semiarid site instrumented down to 7 m, we measured seasonal- and depth-resolved carbon inventories and fluxes and groundwater and unsaturated zone flow rates. Measurements showed that ~30% of the CO2 efflux to the atmosphere (60% in winter) originates from below 1 m, contrary to predictions of less than 1% by Earth System Model land modules. Respiration from deeper roots and deeper microbial communities is supported by favorable subsurface temperatures, moisture, and oxygen availability. Below 1 m, dissolved organic carbon fluxes from the overlying soil and C from deep roots and exudates are expected to be important in sustaining microbial respiration. Because these conditions are characteristic of semiarid climate regions, we contend that Earth System Model land modules should incorporate such deeper soil processes to improve CO2 flux predictions.

AB - Understanding terrestrial carbon cycling has relied primarily on studies of topsoils that are typically characterized to depths shallower than 0.5 m. At a semiarid site instrumented down to 7 m, we measured seasonal- and depth-resolved carbon inventories and fluxes and groundwater and unsaturated zone flow rates. Measurements showed that ~30% of the CO2 efflux to the atmosphere (60% in winter) originates from below 1 m, contrary to predictions of less than 1% by Earth System Model land modules. Respiration from deeper roots and deeper microbial communities is supported by favorable subsurface temperatures, moisture, and oxygen availability. Below 1 m, dissolved organic carbon fluxes from the overlying soil and C from deep roots and exudates are expected to be important in sustaining microbial respiration. Because these conditions are characteristic of semiarid climate regions, we contend that Earth System Model land modules should incorporate such deeper soil processes to improve CO2 flux predictions.

KW - DOC flux

KW - ESM land modules

KW - carbon cycling

KW - carbon fluxes

KW - deep unsaturated zone

KW - semiarid environments

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IS - 9

ER -

Deep Unsaturated Zone Contributions to Carbon Cycling in Semiarid Environments

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Keywords

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