Spatial patterns, storages and sources of black carbon in soils from the catchment of Qinghai Lake, China

Black carbon (BC), composed of char and soot, is an important component of soil organic carbon (SOC), and these materials are potentially important for the global carbon cycle and global climate. A thermal-optical reflectance method was used to determine the spatial patterns of SOC, BC, char and soot in nine soil types collected from 152 sites in the Qinghai Lake catchment. All of the analytes showed large spatial variability: SOC, BC and char were most abundant in bog soils and least abundant in aeolian soils, while soot concentrations in alpine frost desert and in aeolian soils were about half of those in the other soils. The average BC concentration in the 0-20-cm soil layers was 1.3gkg^-1, and BC amounted to 5.6% of the SOC. Char, SOC and BC all decreased with soil depth, but soot showed little variation. The proportions of BC to SOC and char to BC showed contrasting trends in four soil profiles; the former increased and the latter decreased with depth. The quantity of SOC sequestered in topsoils of the catchment area was estimated to be 191Tg; BC accounted for approximately 4.8% of this, and char made up approximately 85% of the total BC stock. The burning of animal dung for domestic cooking apparently was an important source of soil BC: combustion of other biofuels and fossil fuels was the other main source.