Prevalent sediment source shift after revegetation in the Loess Plateau of China: Implications from sediment fingerprinting in a small catchment

As an important soil and water conversation endeavor, the 'Grain for Green' project launched by the Chinese Central Government almost doubled the vegetation cover on the Loess Plateau between 1999 and 2013. The corresponding vegetation restoration considerably diminished slope erosion throughout the Loess Plateau, although erosion in gullies remains poorly understood. In this paper, a composite fingerprinting approach was employed to assess the relative importance of the erosion of gully and slope soils within a typical dam-controlled catchment of the Loess Plateau. A total of 23 couplets were identified based on the deposited layer thicknesses and extreme rainfall event records along the sediment profile. The results suggest that gullies contributed 71% to the overall sediment proportion, and those sediments had an increased tendency to accumulate during 2010-2016 under the 'Grain for Green' project. The sediment inputs from slope areas were predicted to be 29%. The eroded gullies materials mainly consisted of silt-sized particles, which dominated the eroded sediment. Silt particles with sizes of 0.02-0.05 mm constituted the main particles in both deposit sediments and gully materials, whereas the slope areas mainly contained particle sizes of <0.01 mm. The check dam proved to be effective at trapping coarse silt with 27-42% of the total sediment content. This study presents reliable information on the importance of gullies as sediment source materials and verifies the applicability of tracing procedures for collecting information on sediment effluxes from both slopes and gullies.