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Long-term black carbon dynamics in cultivated soil

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Title Long-term black carbon dynamics in cultivated soil
 
Creator Nguyen, B.T.
Lehmann, Johannes
Kinyangi, James
Smernik, R.
Riha, S.J.
Engelhard, M.H.
 
Subject SOIL
CARBON
 
Description Black carbon (BC) is a quantitatively important C pool in the global C cycle due to its relative recalcitrance compared with other C pools. However, mechanisms of BC oxidation and accompanying molecular changes are largely unknown. In this study, the long-term dynamics in quality and quantity of BC were investigated in cultivated soil using X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) techniques. BC particles and changes in BC stocks were obtained from soil collected in fields that were cleared from forest by fire at 8 different times in the past (2, 3, 5, 20, 30, 50, 80 and 100 years before sampling) in western Kenya. BC contents rapidly decreased from 12.7 to 3.8 mg C g−1 soil during the first 30 years following deposition, after which they slowly decreased to a steady state at 3.5 mg C g−1 soil. BC-derived C losses from the top 0.1 m over 100 years were estimated at 6,000 kg C ha−1. The initial rapid changes in BC stocks resulted in a mean residence time of only around 8.3 years, which was likely a function of both decomposition as well as transport processes. The molecular properties of BC changed more rapidly on surfaces than in the interior of BC particles and more rapidly during the first 30 years than during the following 70 years. The Oc/C ratios (Oc is O bound to C) and carbonyl groups (C=O) increased over the first 10 and 30 years by 133 and 192%, respectively, indicating oxidation was an important process controlling BC quality. Al, Si, polysaccharides, and to a lesser extent Fe were found on BC particle surfaces within the first few years after BC deposition to soil. The protection by physical and chemical stabilization was apparently sufficient to not only minimize decomposition below detection between 30 and 100 years after deposition, but also physical export by erosion and vertical transport below 0.1 m.
 
Date 2010-08-05T06:58:48Z
2010-08-05T06:58:48Z
2008-07-11
 
Type Journal Article
 
Identifier Nguyen, B.T.; Lehmann, J.; Kinyangi, J.; Smernik, R.; Riha, S.J.; Engelhard, M.H. 2008. Long-term black carbon dynamics in cultivated soil. Biogeochemistry 89(3):295-308.
0168-2563
https://hdl.handle.net/10568/2173
 
Language en
 
Source Biogeochemistry