Stabilization of organic carbon by complexation with iron colloids formed during biogeochemical weathering of basalt
EMSL Project ID
49797
Abstract
This project is part of a larger, multi-year effort to evaluate the development of spatial and temporal heterogeneity as a result of microbial colonization and biogeochemical weathering of granular basaltic model hillslopes of the Landscape Evolution Observatory (LEO). The triplicate hillslopes (30 m L x 12 m W, and 1 m D) were recently constructed at Biosphere 2 (B2), University of Arizona (UA). The overall goal is to assess the couplings between microbially-mediated rock weathering and C sequestration that occur under controlled-environment hydrologic forcing of the initial stages of soil formation from rock. We hypothesize the observation of "hotspots" where particularly steep gradients in weathering will occur as a result of water movement and flow path development in initially homogeneous, isotropic hillslopes. Soil solution and seepage samples are being collected during and after rainfall events and analyzed to quantify changes in the solution phase composition and mineral saturation states as a result of biotic and abiotic weathering. Solid samples are being collected to determine changes in physical, chemical, mineralogical and microbial properties of the granular basalt, as influenced by landscape position and time. Obtained measurements will be integrated using a coupled hydrological-geochemical model (CrunchFlow + CATHY-NoahMP). Initial data indicates widespread supersaturation of pore solutions with respect to ferric oxyhdyroxide colloids, and we postulate these colloids are stabilizing microbially-derived biomolecules and protecting them from biodegradation. We request access to EMSL facilities and expertise (i) to characterize the spatial distribution of variation in iron solid phase speciation, including oxidation state and mineral structure, and (ii) to investigate the molecular composition of organic matter sequestered in complexes with these Fe-bearing colloids, and its fractionation between solid and aqueous phases in the LEO hillslopes. This will allow us to gain understanding of the processes that are driving accumulation of C and its fractionation due to interactions with the newly forming minerals as soil develops. Previous experiments with the same basalt in the smaller-scale systems demonstrated that 1) significant increase in C concentrations is occurring over short time periods even in the absence of higher plants; 2) abiotic reactions of basalt with the soil solution result in C retention in the solid phase and change in composition of dissolved organic matter; 3) iron oxides are one of the 1st groups of minerals that are being formed as a result of incongruent dissolution of basalt. These findings indicate that there is a strong potential for newly formed iron oxides to influence both quantity and quality of organic matter accumulating in the soils during initial stages of soil formation on basaltic landscapes. We request access at EMSL to the Mossbauer Spectroscopy to characterize oxidation state and bonding environment of iron in weathering basalt in order to trace weathering of Fe-containing phases and precipitation of new minerals and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) for organic matter characterization in solution and soil extracts. These analyses will support a large suite of tests performed at Biosphere 2 and University of Arizona to characterize the interactions between newly formed amorphous and crystalline minerals and organic compounds and their role in C stabilization on the landscapes.
Combining molecular scale measurements made at EMSL with information on hydrologic fluxes, water residence times and saturation states of different mineral phases derived from solution composition will allow us to observe, in real-time, the co-evolution of biological and geochemical structure during initial stages of basalt weathering and formation of pre-soil and to link small-scale biogeochemical processes to landscape-scale manifestations. The proposed project would generate quantitative data on relations among basalt weathering rates and iron oxide precipitation and C sequestration under controlled conditions. Inorganic and organic C sequestration during basalt weathering represents an important sink for atmospheric CO2 on a global scale. Information regarding the mechanisms and rates of this process, generated here by conjunctive measurement and modeling, is essential for understanding earth evolution as well as for predicting future C sequestration.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2017-10-01
End Date
2019-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
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