Response of soil organic carbon to revegetation, engineering measures and extreme rainfall-triggered erosion in an agricultural watershed in the loess tableland–gully region of China

Background and aims Soil and water conservation measures significantly affect soil organic carbon (SOC) worldwide. We aim to study the effects of revegetation, engineering measures and heavy rainstorm–induced erosion on SOC in the different topography. Methods In this study, 405 soil cores from 3 topographic positions (tableland, slope and valley bottom)) under different vegetation types and engineering measures were analyzed through field sampling combined with an indoor test analysis in the Wangdonggou catchment. Results Vegetation and engineering measures increased the soil organic carbon content (SOCC) and soil organic carbon stock (SOCS), but the benefits are different. Rainstorm–induced erosion decreased both the SOCC and SOCS. Specifically, revegetation clearly increased surface SOC but not SOC in deep layers. Compared with that in the eroded area, the SOCC in the 0 ~ 20 cm and 40 ~ 60 cm soil layers increased by 3.31 and 1.61 times after revegetation, respectively. With increasing erosion intensity, the decreasing trends in the SOCC and SOCS were as follows: surface erosion (3.25 g kg⁻¹~ 5.74 g kg⁻¹) > ephemeral gully erosion (3.85 g kg⁻¹~ 5.39 g kg⁻¹) > landslide (1.57 g kg⁻¹~ 3.87 g kg⁻¹). In addition, obvious differences in SOC were observed among the three topographies as follows: valley bottom > tableland > valley slope. Finally, engineering measures increased the SOCC and SOCS by 1.19 ~ 4.24 and 1.32 ~ 3.7 times, respectively. Conclusions Engineering measures and vegetation measures can increase organic carbon, while erosion leads to a decrease in organic carbon.