Effect Of Soil Erosion On Soil Organic Carbon On Sloping Field Of Black Soil Area In Northeast China

Soil organic carbon(SOC) pool is the largest carbon pool of the terrestrial ecosystem, and also is an important CO2 source in the atmosphere. Soil erosion affects the SOC concentration by denudating and transporting soil material, and soil CO2 flux by changing soil temperature and moisture at different positions. It is essential to study the effects of soil erosion on SOC dynamics and CO2 emissions. However, there is still much unknown about related studies. Based on in-site and lab experiments, we selected a small catchment in Black soils of Northeast China to study 1) effects of soil erosion on SOC redistribution on a sloping field; 2) the mineralization of SOC and its relationship with soil temperature and moisture at various slope positions; 3) the characteristic and amount of SOC loss with runoff in erosive events; 4) the applicability of WEPP model in the local, and soil erosion and SOC loss simulated by WEPP model. We obtained the following main conclusions:Soil erosion affected the redistribution of the total SOC in the sloping field. In the surface 30 cm layer shoulder- slope position had the smallest average SOC concentration among all the five slope positions as a result of the severe erosion at this position. In the 0-100 cm layers, SOC concentration decreased with depth at the summit, shoulder- slope and back- slope positions, but decreased first and then increased and decreased again with depth at the foot- slope and toe- slope positions where sediments from the upper eroded slope positions deposited. Soil erosion was a “carbon sink” at the depositional slope positions.There were differences on soil temperature, soil moisture and C mineralization rate among the various slope positions. The C mineralization rate at eroded slope positions was greater than that at the depositional slope positions when soil moisture was high, and soil moisture was the major factor affecting C mineralization. The C mineralization rate at eroded slope positions was similar to that at the depositional slope positions when soil moisture was low, and soil temperature became the most important factor affecting C mineralization. The C mineralization rate from coarse size aggregates at the depositional slope positions was greater than that at eroded slope positions in our incubation study. It was a result of breakdown of coarse aggregates in the wetting process at the beginning of the incubation and lower SOC mineralization rate at the depositional area with higher moisture.The enrichment ratios of SOC in the sediments ranged from 1.45 to 2.16 for the six runoff events. Fine size aggregate fractions in the sediments was significantly greater than that in the source soils, indicating that soil erosion preferentially transport fine soil material. Soil erosion changed the aggregate size fractions and SOC concentration. The erosion was slight based on the erosive events measured in the study area.The Nash-Sutcliffe simulation model efficiency() for the runoff and sediment was 0.83 and 0.62, respectively, showing that the WEPP model was applicable at the studied catchment, and this model simulated better the runoff than the sediment. The simulated net amounts of lost sediments and SOC from the study small catchment for the next fifty years were 27.83 t yr-1 and 0.39 t yr-1, respectively. The result helps to evaluate the amount of SOC loss with runoff and make measures for soil and water conservation for the local.