Solid State NMR Characterization of SOC in a Subalpine Forest Wetland to Determine Mobility
EMSL Project ID
48717
Abstract
The influence of wetland soils on the global carbon cycle is greatly underestimated. As hydrological regimes are predicted to change with a warming global environment, understanding the impact of climatic changes on terrestrial carbon pools will be essential for predictive models. Forest and grasslands have been investigated in multiple studies for turnover rates of soil organic carbon (SOC). Yet grasslands and forest litter only represent a fraction of the SOC pools. Wetlands are the largest terrestrial carbon pool and control more than a third of inputs and outputs from terrestrial carbon. These precious soils are even more critical and unique in that they undergo reduction-oxidation (redox) oscillations due to wetting and drying cycles. Iron minerals are ubiquitous in soils, highly redox sensitive, and important sorbents for contaminants, nutrients and SOC in the environment. To date, few studies have characterized the impact of changing redox potential and reductive iron dissolution on the mobility of SOC. In order to monitor SOC mobility at the field scale, the proposed research aims to characterize SOC spatially and with depth across a moisture transect in a subalpine wetland. Use of 13C CP-MAS NMR will give important structural details of the SOC in the field site. This same isolated and characterized SOC will be used in detailed lab studies to corroborate the field results. Synthetic iron and aluminum oxides with and without sorbed SOC will be retrieved temporally from the field setting to determine the type and amount of SOC associated with the mineral surface. Soil redox potential will be measured and the change in mineralogy determined using synchrotron based EXAFS. In this way, the authors hope to elucidate the impacts of iron redox processes on the fate of SOC. In detailed lab studies, iron and aluminum (control) oxides with and without sorbed HS (isolated from the field site) will be subjected to a continuous stirred tank-reactor (CSTR) containing aqueous Fe2+ (to poise the redox potential in systems containing Fe(III) minerals) and DOC. Retrieval of the minerals in this controlled setting will be analyzed for C structural differences as a function of reductive iron dissolution and compared to the field samples. The authors aim to bridge the gap between large field scale interactions and lab studies by duplicating field settings in a manipulated CSTR. Improved understanding of the interaction between chemical moieties within the SOC and iron minerals will help elucidate the mobility of SOC in wetland soils which is of importance for predicting water quality and C cycling.
Project Details
Project type
Limited Scope
Start Date
2014-12-23
End Date
2015-02-22
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Daugherty E.E., G.A. Mckee, R. Bergstrom, S.D. Burton, C. Pallud, R.M. Hubbard, and E.F. Kelly, et al. 2019. "Hydrogeomorphic controls on soil carbon composition in two classes of subalpine wetlands." Biogeochemistry 145, no. 1-2:161–175. PNNL-SA-145302. doi:10.1007/s10533-019-00597-y