Effects of water erosion on soil organic carbon stability in the subtropical China

Abstract

How the stability of soil organic carbon (SOC) is affected by soil erosion is still not clear. The main purpose of this study was to characterize how SOC stability is affected by erosion and assess the effects of different soil properties on SOC stability. Soils from eroding and depositional sites in a typical small watershed in subtropical China were collected, and soil samples from four different depths (0–5, 5–10, 20–30, and 120–150 cm) were selected to represent the profile. Soil physicochemical properties as well as soil organic matter (SOM) chemical structure were measured. Thermal analysis and mineralization incubation experiments were performed to study the SOM stability. The effects of the soil properties on the SOM stability were evaluated via redundancy analysis. The results showed that the eroding and depositional sites had different SOC contents but had similar organic functional groups. Furthermore, the OC in the eroded soils was more stable than that in the deposited soils, but this difference was only observed in the surface layers (0–5 and 5–10 cm). The selected variables (including soil texture, bulk density, pH, SOC, dissolved organic carbon (DOC), iron, soil aggregates, depth, erosion, and deposition) significantly explained the variations in SOC stability. A total of 91.4% of the variation in the thermogravimetry (TG)-T50 (the temperature resulting in 50% of SOM loss) and 98.9% of the variation in the CO2 emissions were explained by these variables. SOC alone contributed to 68% of the variation in the TG-T50, whereas DOC individually contributed 93.9% of the variation in the CO2 emissions. SOC and DOC contents are the most important soil properties influencing SOC stability, and SOC stability affected by soil erosion is mainly by displacing SOM.