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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, here we measured seasonal- and depth-resolved carbon inventories and fluxes and groundwater and unsaturated zone flow rates. Measurements showed that ~30% of the CO 2 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. Finally, 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 CO 2 flux predictions.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1];  [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth and Environment Sciences Area
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1479368
Alternate Identifier(s):
OSTI ID: 1472185
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Biogeosciences
Additional Journal Information:
Journal Volume: 123; Journal Issue: 9; Journal ID: ISSN 2169-8953
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; carbon cycling; deep unsaturated zone; semiarid environments; carbon fluxes; ESM land modules; DOC flux

Citation Formats

Wan, Jiamin, Tokunaga, Tetsu K., Dong, Wenming, Williams, Kenneth H., Kim, Yongman, Conrad, Mark E., Bill, Markus, Riley, William J., and Hubbard, Susan S. Deep Unsaturated Zone Contributions to Carbon Cycling in Semiarid Environments. United States: N. p., 2018. Web. doi:10.1029/2018JG004669.
Wan, Jiamin, Tokunaga, Tetsu K., Dong, Wenming, Williams, Kenneth H., Kim, Yongman, Conrad, Mark E., Bill, Markus, Riley, William J., & Hubbard, Susan S. Deep Unsaturated Zone Contributions to Carbon Cycling in Semiarid Environments. United States. doi:10.1029/2018JG004669.
Wan, Jiamin, Tokunaga, Tetsu K., Dong, Wenming, Williams, Kenneth H., Kim, Yongman, Conrad, Mark E., Bill, Markus, Riley, William J., and Hubbard, Susan S. Tue . "Deep Unsaturated Zone Contributions to Carbon Cycling in Semiarid Environments". United States. doi:10.1029/2018JG004669. https://www.osti.gov/servlets/purl/1479368.
@article{osti_1479368,
title = {Deep Unsaturated Zone Contributions to Carbon Cycling in Semiarid Environments},
author = {Wan, Jiamin and Tokunaga, Tetsu K. and Dong, Wenming and Williams, Kenneth H. and Kim, Yongman and Conrad, Mark E. and Bill, Markus and Riley, William J. and Hubbard, Susan S.},
abstractNote = {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, here 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. Finally, 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.},
doi = {10.1029/2018JG004669},
journal = {Journal of Geophysical Research. Biogeosciences},
number = 9,
volume = 123,
place = {United States},
year = {2018},
month = {9}
}

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