A radioisotope - enabled reactive transport model for deep vadose zone carbon
In mountainous regions, which constitute the principle source of recharge to major rivers and regional aquifers, infiltration occurs through fractured, partially saturated, weathered bedrock that acts as a boundary layer between saturated aquifers and surface soil. Commonly this deep vadose zone (DVZ) is many meters thick, and yet its role in regulating the generation, retention and mobility of reactive solutes, including nutrients, contaminants and weathering products, is largely unknown. In particular, many of the key reactions that drive the formation of the weathered DVZ and the quality of water moving through it are redox processes, regulated by the availability of organic carbon and oxygen below the soil layer. The role of the DVZ is thus also poorly constrained in the context of carbon stocks and mobility, particularly in lithologies that are naturally high in organic carbon, such as shales. The overarching hypothesis of this study is that upland regions developed in geologic settings with abundant petrogenic carbon store and actively cycle carbon in the weathered DVZ below the soil and above the water table at rates that are significant and currently unconstrained. In order to quantify this cycling, the current study combines novel instrumentation techniques allowing new direct sampling of DVZ systems with advanced numerical reactive transport simulations of carbon transport and transformation. Critically, these simulations will explicitly treat the three isotopes of carbon (the abundant 12C, the stable rare 13C and the radioactive 14C) in a unified framework, thus clearly parsing between the contributions of modern surface derived carbon and lithologic carbon sources in integrated measurements of fluid and gas phase fluxes. This novel model capability will be applied to test the role of DVZ carbon cycling as a regulator of water quality and geological weathering in two complementary field sites both located in organic carbon rich shale lithologies. The first is the Eel River Critical Zone Observatory (ERCZO) in Mendocino County, California, and the second is the Lawrence Berkeley National Laboratory Watershed Function Scientific Focus Area (SFA) in the East River watershed, near Crested Butte, Colorado. At the ERCZO, a novel vadose zone monitoring system has been installed in a 20 m thick, partially saturated, weathered shale hillslope, and preliminary data already indicate substantial CO2 flux generated many meters below the soil surface. At the SFA field site, an instrumented hillslope transect indicates a more complex multi-dimensional fluid and solute transport regime, which will serve as a key test of the calibrated models. Collectively, this project will advance understanding of the cycling of carbon belowground and in relation to transport pathways across the poorly constrained DVZ characteristic of primary water recharge areas. The key product of this work will be enhanced isotope simulation capabilities that are robust and publicly available for application across a broad diversity of systems.
- Research Organization:
- Board of Trustees of the University of Illinois, Champaign, IL
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER)
- Contributing Organization:
- United States Geological Survey University of Texas at Austin
- DOE Contract Number:
- SC0019198
- OSTI ID:
- 1902870
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- DOE-UIUC-SC0019198
- Country of Publication:
- United States
- Language:
- English
Development of soil radiocarbon profiles in a reactive transport framework
|
journal | August 2021 |
On the utility of quantitative modeling to the interpretation of Ca isotopes
|
journal | March 2020 |
Carbon Dioxide Production in Bedrock Beneath Soils Substantially Contributes to Forest Carbon Cycling
|
journal | December 2020 |
Microbially mediated kinetic sulfur isotope fractionation: reactive transport modeling benchmark
|
journal | August 2020 |
Stable Isotope Fractionation by Transport and Transformation
|
journal | September 2019 |
Similar Records
The weathered bedrock vadose zone: A hidden control on water availability in the western United States (Final Technical Report)
Sulfur Biogeochemical Cycling and Redox Dynamics in a Shale-Dominated Mountainous Watershed