Characterizing Biodegradable Organic Carbon Mobilized from the Sediments of an Arsenic-Contaminated Aquifer in Bangladesh: Augmenting Spectroscopic Methods with FT-ICR-MS
EMSL Project ID
48515
Abstract
For over a decade, researchers have debated the source of organic carbon fueling microbial reactions responsible for mobilizing arsenic off aquifer sediments into groundwater within the deltaic environments of South and Southeast Asia. The debate centers on the involvement of sedimentary organic carbon co-deposited when the aquifers were formed versus that of surface derived carbon transported into the subsurface with recharging water. Identifying the source of organic carbon involved with arsenic mobilization is important because it clarifies if human activities can affect the arsenic-contamination problem. We recently documented the existence of biodegradable organic carbon in sediments of an arsenic-contaminated aquifer in Bangladesh. The work suggests that in situ perturbations to the aquifer matrix could promote mobilization of bioavailable sedimentary organic carbon that can fuel microbial reactions. Conceptually, this pool of stabilized sedimentary organic carbon bridges the apparently conflicting lines of evidence that implicate either surface organic carbon or sedimentary organic carbon in fueling microbial activity associated with arsenic mobilization into groundwater. However, beyond bioavailability, we do not understand the character of this destabilized pool of sedimentary organic carbon. We are currently using tools available in our research lab to characterize the released organic carbon: specific ultraviolet absorption, fluorescence spectroscopy to develop excitation-emission matrices, and spectral slope ratios. Our goal is to understand the initial character of the mobilized organic carbon and track how its composition changes over time as it is degraded by microbes so we can 1) identify in situ processes (physical and chemical) that can destabilize organic carbon off aquifer sediment, and 2) predict how destabilization will impact subsurface biogeochemistry. While the techniques available to us in our own research lab are useful for probing carbon characteristics (e.g., aromaticity), they do not allow us to assess molecular-scale information about our pool of mobilized organic carbon. We propose to augment our ongoing carbon characterization methods with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), a technique available at the Environmental Molecular Sciences Laboratory (EMSL). FT-ICR-MS will allow us to identify functional groups and elemental composition of the organic carbon mobilized into porewater and then degraded over time in our experiment. The combination of spectroscopic methods with FT-ICR-MS will create a comprehensive understanding of the mobilized sedimentary organic carbon, and will provide a unique opportunity to directly compare carbon characterization techniques within a controlled experimental system where carbon bioavailability was functionally assessed.
Project Details
Project type
Limited Scope
Start Date
2014-08-01
End Date
2014-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Henske JK, SP Gilmore, D Knop, FJ Cunningham, JA Sexton, CR Smallwood, V Shutthanandan, JE Evans, MK Theodorou, and MA O'Malley. 2018. "Transcriptomic characterization of Caecomyces churrovis: a novel, non-rhizoid-forming lignocellulolytic anaerobic fungus." PNNL-SA-134108, Pacific Northwest National Laboratory, Richland, WA. [Unpublished]
Pracht L., M.M. Tfaily, B. Ardissono, and R.B. Neumann. 2018. "Molecular characterization of organic matter mobilized from Bangladeshi aquifer sediment: tracking carbon compositional change during microbial utilization." Biogeosciences 15, no. 6:1733-1747. PNNL-SA-133552. doi:10.5194/bg-15-1733-2018
Pracht L., M.M. Tfaily, B. Ardissono, and R.B. Neumann. 2018. "Molecular characterization of organic matter mobilized from Bangladeshi aquifer sediment: tracking carbon compositional change during microbial utilization." Biogeosciences 15, no. 6:1733-1747. PNNL-SA-133552. doi:10.5194/bg-15-1733-2018