Mössbauer Spectroscopic Characterization of Fe Redox Process in Soil Minerals Coupled with Organic Matter Transformation in O2 Fluctuating Soils
EMSL Project ID
60583
Abstract
Recent studies estimate that soil is one of the three largest reservoirs of organic matter (OM) on Earth. Soil carbon is a highly dynamic carbon repository, and its turnover has a major impact on carbon cycle and global climate. Virtually all of this soil carbon is associated with minerals via various mechanisms. Association with minerals is known to decelerate OM decomposition because of its protection against microbial oxidation, but various mechanisms exist to release OM from such associations, ultimately returning C from soil to the atmosphere as CO2. Recent observations have revealed that Fe redox cycling and SOM transformation are coupled in redox fluctuating environments, but specific mechanisms for such coupling have not been well understood.The specific aim of this project is to understand how Fe redox cycle drives SOM transformation; and 2) how SOM transformation affects Fe redox cycling in O2 fluctuating soils. We hypothesize that in soils mineral-bound Fe(II) plays a greater role than aqueous Fe2+ in generation of reactive oxygen species (ROS) and decomposition of SOM to more bioavailable organic compounds. We further hypothesize that SOM affects the kinetics and mechanisms of abiotic Fe(II) oxidation and biotic Fe(III) reduction. We will test these hypotheses by performing a mechanistic study of Fe-SOM interactions using pure minerals, microbial community extract, and SOM extract. To accomplish this task, abiotic Fe(II) oxidation experiment will be performed in the presence of SOM extract. Time-course changes of Fe(II), ROS, CO2, and DOC/TOC will be monitored. Aqueous SOM will be fully characterized using IC and HPLC, excitation emission spectroscopy, FT-ICR-MS, and solution NMR. FTIR, XPS, and ToF-SIMS will be used to characterize mineral-associated SOM. Fe speciation and mineralogy will be characterized by XRD, SEM, TEM, and Mössbauer spectroscopy. The requested EMSL resources are essential to characterize the interactions among minerals, SOM, and bacteria to understand the mechanisms and pathways of their interactions. All data types will be integrated and multiple correlations will be made between SOM transformation and Fe redox cycling rate/extent to test the hypotheses and to develop predictive capabilities.
This proposal is a first step towards our contribution to earth system models by incorporating the mineralogy control of OM availability in order to better predict the response of soil carbon stocks to anticipated climate warming. The reservoir size and residence time of mineral-associated soil carbon represents a critical element of any attempt to control carbon flow through the biosphere for the purposes of reducing anthropogenic CO2 concentration in the atmosphere. Mineral-OM association also controls the aqueous transport of OM, the bioavailability of OM to microorganisms, and the reactivity of OM towards contaminant migration and nutrient cycling. Therefore, this research contributes to our molecular-level understanding of the fate of soil OM with important implications for environmental challenges and national energy needs.
Project Details
Project type
Limited Scope
Start Date
2022-10-10
End Date
2023-01-08
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members