Spatial distributions and sequestrations of organic carbon and black carbon in soils from the Chinese loess plateau

Concentrations of soil organic carbon (SOC), black carbon (BC), char, and soot in topsoils (0–20 cm) and vertical soil profiles (0–100 cm) from the Chinese Loess Plateau (CLP) were investigated. Objectives of the study were to establish the spatial distributions and estimate the sequestrations of these substances. The SOC, BC, char and soot concentrations were higher in the eastern and southeastern parts of the plateau and lower in the north, which is consistent with the patterns of economic development and energy consumption. The highest average SOC concentration was found in the clayey loess zone, followed by the loess and sandy loess zones. Similar trends were observed for BC, char and soot, suggesting interactions with clay and silt are potentially important influences on OC and BC. The SOC contents in topsoils varied from 0.31 to 51.81 g kg− 1, with a mean value of 6.54 g kg− 1, while BC and char concentrations were 0.02 to 5.5 g kg− 1 and 0.003 to 4.19 g kg− 1, respectively, and soot ranged from 0.01 to 1.32 g kg− 1. Unlike SOC, both BC and char decreased with soil depth, whereas soot showed little variation with depth. BC and char were correlated in the topsoils, and both correlated moderately well with SOC (R2 = 0.60) and soot (R2 = 0.53). The SOC pools sequestered in the 0 to 20 cm and 0 to 100 cm depths were estimated to be 0.741 and 3.63 Pg, respectively, and the BC pools sequestered in the 0 to 20 cm and 0 to 100 cm depths were 0.073 and 0.456 Pg, respectively. Therefore the quantity of carbon stored in the sediments of the CLP evidently exceeds 109 tons. The char contained in the upper 20 cm layer was 0.053 Pg, which amounted to 72.5% of the BC in that layer.

► There was a wide variability of SOC, BC, char and soot in the soils from the CLP.
► The highest SOC concentrations were found in the clayey loess zone.
► There was far more char than soot when BC was partitioned into char and soot.
► There was a strong correlation between char and BC.