DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Carbon Dioxide Production in Bedrock Beneath Soils Substantially Contributes to Forest Carbon Cycling

Journal Article · · Journal of Geophysical Research. Biogeosciences

Soils are widely considered the primary terrestrial organic matter pool mediating carbon transactions with the atmosphere and groundwater. Because soils are both a host and a product of rhizosphere activity, they are thought to mark the location where photosynthetic fixation of carbon dioxide (CO2) is balanced by the oxidation of organic matter. However, in many terrestrial environments, the rhizosphere extends below soils and into fractured bedrock, and it is unknown if the resulting biological and hydrologic dynamics in bedrock have a significant impact on carbon cycling. Here we show substantial production of CO2 in weathered bedrock at 4–8 m below the thin soils (<0.5 m thick) of a Northern California forest using innovative monitoring technology for sampling gases and water in fractured rock. The deep CO2 production supports a persistent upward flux of CO2(g) year-round from bedrock to soil, constituting between 2% and 29% of the average daily CO2 efflux from the land surface. When water is rapidly transported across the fractured bedrock vadose zone, nearly 50% of the CO2 produced in the bedrock dissolves into water, promoting water-rock interaction and export of dissolved inorganic carbon (DIC) from the unsaturated zone to groundwater, constituting as much as 80% of the DIC exiting the hillslope. Such CO2 production in weathered bedrock is subject to unique moisture, temperature, biological, and mineralogical conditions which are currently missing from terrestrial carbon models.

Research Organization:
Univ. of Illinois at Urbana-Champaign, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC); National Science Foundation (NSF); USDOE
Grant/Contract Number:
SC0019198; EAR 1331940; DE‐SE001919; DE‐SC0019198
OSTI ID:
1734383
Alternate ID(s):
OSTI ID: 1786722; OSTI ID: 1852930
Journal Information:
Journal of Geophysical Research. Biogeosciences, Vol. 125, Issue 12; ISSN 2169-8953
Publisher:
American Geophysical UnionCopyright Statement
Country of Publication:
United States
Language:
English

References (50)

Molecular and isotopic composition of modern soils derived from kerogen-rich bedrock and implications for the global C cycle journal March 2019
The Case for Digging Deeper: Soil Organic Carbon Storage, Dynamics, and Controls in Our Changing World journal April 2019
Unexpected large evasion fluxes of carbon dioxide from turbulent streams draining the world’s mountains journal October 2019
The hidden organic carbon in deep mineral soils journal January 2013
Weathering of rock to regolith: The activity of deep roots in bedrock fractures journal August 2017
Origin and Distribution of Carbon Dioxide in the Unsaturated Zone of the Southern High Plains of Texas journal September 1984
Field evidence for climate-driven changes in sediment supply leading to strath terrace formation journal May 2009
Gas diffusivity and production of CO2 in deep soils of the eastern Amazon journal November 1995
Using O 2 to study the relationships between soil CO 2 efflux and soil respiration journal January 2015
The global carbon dioxide flux in soil respiration and its relationship to vegetation and climate journal April 1992
Carbon Exports from Terrestrial Ecosystems: A Critical-Zone Framework journal April 2019
Improving understanding of soil organic matter dynamics by triangulating theories, measurements, and models journal July 2018
Rain, rock moisture dynamics, and the rapid response of perched groundwater in weathered, fractured argillite underlying a steep hillslope: MOISTURE DYNAMICS AND GROUNDWATER IN WEATHERED ROCK journal November 2012
CO2 evasion along streams driven by groundwater inputs and geomorphic controls journal October 2018
Flexible Time Domain Reflectometry Probe for Deep Vadose Zone Monitoring journal May 2003
Steady-State Aerobic Microbial Activity as a Function of Soil Water Content journal January 1990
Feedbacks among O2 and CO2 in deep soil gas, oxidation of ferrous minerals, and fractures: A hypothesis for steady-state regolith thickness journal February 2017
Soil respiration and georespiration distinguished by transport analyses of vadose CO 2 , 13 CO 2 , and 14 CO 2 journal June 1998
Factors controlling seasonal groundwater and solute flux from snow-dominated basins journal June 2018
Hydrologic regulation of plant rooting depth journal September 2017
Long-term pattern and magnitude of soil carbon feedback to the climate system in a warming world journal October 2017
Managing uncertainty in soil carbon feedbacks to climate change journal July 2016
Worldwide distribution of continental rock lithology: Implications for the atmospheric/soil CO 2 uptake by continental weathering and alkalinity river transport to the oceans: WORLD WIDE DISTRIBUTION OF CONTINENTAL ROCK LITHOLOGY journal April 2003
Deep Vadose Zone Respiration Contributions to Carbon Dioxide Fluxes from a Semiarid Floodplain journal January 2016
Technical note: In situ measurement of flux and isotopic composition of CO2 released during oxidative weathering of sedimentary rocks journal January 2018
Chemical reactions, porosity, and microfracturing in shale during weathering: The effect of erosion rate journal January 2020
Deep soil organic matter—a key but poorly understood component of terrestrial C cycle journal May 2010
Water percolation through the deep vadose zone and groundwater recharge: Preliminary results based on a new vadose zone monitoring system: WATER PERCOLATION THROUGH DEEP VADOSE ZONE journal May 2007
Projected land photosynthesis constrained by changes in the seasonal cycle of atmospheric CO2 journal September 2016
The contentious nature of soil organic matter journal November 2015
‘One physical system’: Tansley's ecosystem as Earth's critical zone journal March 2015
Relating soil gas to weathering using rock and regolith geochemistry journal September 2018
Constraining the subsoil carbon source to cave-air CO 2 and speleothem calcite in central Texas journal November 2017
The ecohydrology of roots in rocks journal January 2010
Process dominance shift in solute chemistry as revealed by long-term high-frequency water chemistry observations of groundwater flowing through weathered argillite underlying a steep forested hillslope journal September 2014
Proton-binding study of standard and reference fulvic acids, humic acids, and natural organic matter journal January 2003
A considerable fraction of soil-respired CO2 is not emitted directly to the atmosphere journal September 2018
Reviews and syntheses: on the roles trees play in building and plumbing the critical zone journal January 2017
Controls on solute concentration-discharge relationships revealed by simultaneous hydrochemistry observations of hillslope runoff and stream flow: The importance of critical zone structure: C-Q RELATIONSHIPS OF ELDER CREEK journal February 2017
Dynamic, structured heterogeneity of water isotopes inside hillslopes journal January 2016
Direct observations of rock moisture, a hidden component of the hydrologic cycle journal February 2018
Aquatic carbon cycling in the conterminous United States and implications for terrestrial carbon accounting journal December 2015
Soil solution pH measurements using in-line chambers with tension lysimeters journal May 2000
Using respiration quotients to track changing sources of soil respiration seasonally and with experimental warming journal January 2020
Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks journal July 2017
Deep Unsaturated Zone Contributions to Carbon Cycling in Semiarid Environments journal September 2018
Gas and vapour movements in the soil: I. The diffusion of vapours through porous solids journal July 1940
Prediction of pH Errors in Soil-water Extractors Due to Degassing journal January 1987
A review of the molecular diffusivities of H2O, CO2, CH4, CO, O3, SO2, NH3, N2O, NO, and NO2 in air, O2 and N2 near STP journal March 1998
Snowmelt controls on concentration-discharge relationships and the balance of oxidative and acid-base weathering fluxes in an alpine catchment, East River, Colorado: ACID-BASE VERSUS OXIDATIVE WEATHERING FLUXES journal March 2017