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 mechanisms controlling the stability and dynamics of NOM in low-carbon sediments.
Surface soils typically contain 5-10% levels of organic carbon (OC), but OC concentrations in sediments more than 1 meter 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 natural organic matter (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 in order 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 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 (non-extractable) OC fractions, indicating an increase in NOM stability correlated with greater metal complexation, apparent molecular weight, and aromaticity.
BER PM Contact
David Lesmes, SC-23.1, 301-903-2977
Lawrence Berkeley National Laboratory
Funding for this study was provided by the U.S. Department of Energy, BER Contract DE-AC020SCH11231 to the LBNL Sustainable Systems Scientific Focus Area.
P.M. Fox, 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]
Fox, Patricia; Nico, Peter; Tfaily, Malak; Heckman, Katherine; Davis, James (2017), “Data for: Characterization of Natural Organic Matter in Low-Carbon Sediments: Extraction and Analytical Approaches”, Mendeley Data, [DOI: 10.17632/5f3hbm69w6.2]
SC-23.1 Climate and Environmental Sciences Division, BER
BER supports basic research and scientific user facilities to advance DOE missions in energy and environment. More about BER
Aug 24, 2019
New Approach for Studying How Microbes Influence Their Environment
A diverse group of scientists suggests a common framework and targeting of known microbial processes [more...]
Aug 08, 2019
Nutrient-Hungry Peatland Microbes Reduce Carbon Loss Under Warmer Conditions
Enzyme production in peatlands reduces carbon lost to respiration under future high temperatures. [more...]
Aug 05, 2019
Amazon Forest Response to CO2 Fertilization Dependent on Plant Phosphorus Acquisition
AmazonFACE Model Intercomparison. The Science Plant growth is dependent on the availabi [more...]
Jul 29, 2019
A Slippery Slope: Soil Carbon Destabilization
Carbon gain or loss depends on the balance between competing biological, chemical, and physical reac [more...]
Jul 15, 2019
Field Evaluation of Gas Analyzers for Measuring Ecosystem Fluxes
How gas analyzer type and correction method impact measured fluxes. The Science A side- [more...]
List all highlights (possible long download time)