Assessment of soil erosion in a small catchment of the transitional zone between the Mongolian Plateau and the North China Plain using check dam deposits

Abstract

Soil erosion in the transitional zone between the Mongolian Plateau and the North China Plain has persisted owing to complex natural conditions and human activity. Ecological restorative measures such as the conversion of slope farmland to fallow and minimization of grazing via enclosures are typically adopted in this region to avoid further land degradation. However, soil erosion and sediment delivery continue even after such measures are implemented. In this study, a 1.34 km² catchment that has been seriously affected by erosion was investigated to assess soil erosion processes and dynamics following the construction of cascading check dams. Sediments along the check dams that were deposited during the period 2013–2019 were collected and analyzed for sediment source differentiation and deposition, sediment layers were correlated with major rainfall events to calculate the contribution rates of different source areas using sediment source fingerprinting, and sediment sources and erosion dynamics were compared at different stages following ecological restoration. The results indicated that sediments were deposited during five major phases from 2013 to 2019, with relative contribution rates of 30.2%, 38.9%, and 30.9%, and relative contributions per unit area of 0.6, 0.9, and 13.7 obtained for grasslands, forests, and gully areas, respectively. Precipitation, especially daily rainfall over 25 mm, was the primary driver of sediment contribution, with vegetation cover, represented by the normalized difference vegetation index (NDVI), playing a minor role. A general decrease in the erosion rate was observed for forests; however, the sediment contribution in the gullies indicated increased erosion over the period 2013–2019, while the erosion rates stabilized in sandy grasslands over the same period. This study highlights the potential effectiveness of ecological restoration in curbing the expansion of sandy grassland, and provides a basis for the planning and construction of ecological restorative projects in the transitional zone in the future.