Efforts to characterize carbon stored in sediments below 1 meter are critical for understanding the mechanisms that control the stability and dynamics of the largest fraction of the Earth’s total carbon pool.
Organic carbon concentrations in sediments more than 1 meter below the land surface are typically 10 to 200 times lower than in surface soils, posing a distinct challenge for characterization. A range of chemical extractions were evaluated for extraction of natural organic matter (NOM) from low-carbon (<0.2%) alluvial sediments. Additionally, an extraction and purification scheme was developed in order to isolate and characterize different fractions of sediment-associated NOM.
Using a combination of analytical approaches, high-quality chemical characterization data was collected on NOM from understudied low-carbon sediments. The developed approach can be used to provide insight into the stability and dynamics of NOM in low-carbon sediments.
Surface soils typically contain 5% to 10% levels of organic carbon (OC), but OC concentrations in sediments more than 1 m below the land surface are often 10 to 200 times lower, and the usual techniques to measure the chemical characteristics of OC in these sediments are not sufficiently sensitive. In this study, a range of chemical extractions were evaluated for extraction of NOM from two low-carbon (<0.2%) alluvial sediments. The OC extraction efficiency followed the order pyrophosphate (PP) > NaOH > HCl, hydroxylamine hydrochloride > dithionite, water. A NOM extraction and purification scheme was developed using sequential extraction with water (MQ) and sodium pyrophosphate at pH 10 (PP), combined with purification by dialysis and solid-phase extraction to isolate different fractions of sediment-associated NOM. Characterization of these pools of NOM for metal content and by Fourier transform infrared spectroscopy (FITR) showed that the water-soluble fraction (MQ-SPE) had a higher fraction of aliphatic and carboxylic groups, while the PP-extractable NOM (PP-SPE and PP > 1kD) had higher fractions of C=C groups and higher residual metals. This trend from aliphatic to more aromatic is also supported by the specific ultraviolet (UV) absorbance at 254 nm (SUVA254) (3.5 vs 5.4 for MQ-SPE and PP-SPE, respectively) and electrospray ionization Fourier transform ion cyclotron resonance spectrometry (ESI-FTICR-MS) data, which showed a greater abundance of peaks in the low O/C and high H/C region (0–0.4 O/C, 0.8–2.0 H/C) for the MQ-SPE fraction of NOM. Radiocarbon measurements yielded standard radiocarbon ages of 1020, 3095, and 9360 years BP for PP-SPE, PP > 1kD, and residual (nonextractable) OC fractions, indicating an increase in NOM stability correlated with greater metal complexation, apparent molecular weight, and aromaticity.
BER Program Manager
Lawrence Berkeley National Laboratory
Funding for this study was provided by the Subsurface Biogeochemical Research program of the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science, under Contract No. DE-AC020SCH11231 to the Lawrence Berkeley National Laboratory Sustainable Systems Scientific Focus Area.
Fox, P. M. , P. S. Nico, M. M. Tfaily, K. Heckman, and J. A. Davis, “Characterization of natural organic matter in low-carbon sediments: Extraction and analytical approaches.” Organic Geochemistry 114, 12–22 (2017). [DOI:10.1016/j.orggeochem.2017.08.009].
Data Archive: Fox, Patricia; Nico, Peter; Tfaily, Malak; Heckman, Katherine; Davis, James. “Data for: Characterization of natural organic matter in low-carbon sediments: Extraction and analytical approaches,” Mendeley Data (2017). [DOI:10.17632/5f3hbm69w6.2].
SC-33.1 Earth and Environmental Sciences Division, BER
BER supports basic research and scientific user facilities to advance DOE missions in energy and environment. More about BER
Mar 23, 2021
Molecular Connections from Plants to Fungi to Ants
Lipids transfer energy and serve as an inter-kingdom communication tool in leaf-cutter ants&rsqu [more...]
Mar 19, 2021
Microbes Use Ancient Metabolism to Cycle Phosphorus
Microbial cycling of phosphorus through reduction-oxidation reactions is older and more widespre [more...]
Feb 22, 2021
Warming Soil Means Stronger Microbe Networks
Soil warming leads to more complex, larger, and more connected networks of microbes in those soi [more...]
Jan 27, 2021
Labeling the Thale Cress Metabolites
New data pipeline identifies metabolites following heavy isotope labeling.
Aug 31, 2020
Novel Bacterial Clade Reveals Origin of Form I Rubisco
List all highlights (possible long download time)