Saturday, 15 July 2006

Importance of Kerogen Carbons in Soils and Sediments from the Pearl River Delta and Estuary, China.

Yong Ran1, Ke Sun1, and Baoshan Xing2. (1) Guangzhou Institute of Geochemistry, P O Box 1131, 511 Kehuajie, Tianhe District, Guangzhou, 510640, China, (2) Dept of Plant, Soil, and Insect Sciences, Univ of Massachusetts, Stockbridge Hall, Amherst, MA 01003

The NonHydrolyzable Carbons (NHC) in three contaminated soils from the urban area of Guangzhou and in twenty-two bulk and size-fractionated sediments from the Pearl River Delta and Estuary, China, were measured upon treatments with a revised HCl/HF/trifluoroacetic acid method. The isolated NHC fractions were also characterized using elementary analysis, solid state 13C cross-polarization and magic angle spinning nuclear magnetic resonance spectroscopy (13C-CP/MAS NMR), Fourier Transformed InfraRed spectroscopy (FTIR), and Raman microspectrometry. The results showed that NHC accounted for 25.6 %-84.7 % of total organic carbon (OC) in the soils and sediments. The NHC contents were highly correlated with the OC contents for the high OC (OC>1 %) and the low OC (OC<1 %) samples, respectively, exhibiting a higher slope (0.692) and a lower slope (0.357). Systematic characterization showed that NHC composed mainly of the type of kerogen III derived from higher plant materials and oxidized to a certain extent in the earth surface environment. NHC had relatively low O/C and H/C atomic ratios, minor or negligible oxygen-containing functional groups, and different amorphous and graphitic carbon Raman peaks, showing varied degree of organic matter maturation. It is feasible that kerogen can be separated from soils, bulk and size-fractionated sediments with the revised hydrolysis procedure. The kerogen carbon is important or even dominating components of OC in the soils and sediments. The highly correlation between NHC and OC, obtained for the first time, has implication to biogeochemical processes of hydrophobic organic contaminants and organic carbons in the surface aquatic and fluvial environments.

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