Sediment connectivity of small watershed affected by gully development and vegetation restoration on the loess plateau

Sediment connectivity can reflect the linkage between sediment source and sink, and identify the hotspot of soil conservation in watersheds. Potential effects of gully development and vegetation restoration on sediment connectivity are not fully understood. This study was performed to quantify the temporal changes in sediment connectivity reflected by the index of connectivity (IC) triggered by the coupling effect of gully development and vegetation restoration in a representative small watershed in the Loess Plateau. Google maps and Landsat images were used to determine gully characteristics and vegetation coverage. Based on the source-sink landscape index, weights of different land use types were computed using the K and C factors of the Universal Soil Loess Equation to calculate the IC. Partial least squares regression was used to quantify the contribution of gully development and vegetation restoration to the IC. The results showed that IC decreased significantly from −1.27 in 2000 to −8.15 in 2020 due to rapid vegetation restoration. Sediment connectivity increased with slope gradient but decreased with vegetation coverage. Compared with grassland, sediment connectivity decreased by 0.35–2.86 for cropland and 1.29–3.56 for forestland from 2000 to 2020. Moreover, the length, width, circumference, and area of gullies increased by at least 73% from 2000 to 2010, and the rate of increase declined greatly with the effective implementation of vegetation restoration. With the increase in slope gradient, gully development became more intense, and the IC increased. The gully length, width, circumference and area, and IC of shady and semi-shady slope aspects were 27.25%, 23.29%, 26.76% and 61.46%, and 5.8%–18.6% less than that of sunny and semi-sunny slope aspects. Vegetation restoration inhibited sediment connectivity, whereas gully development promoted sediment connectivity. Overall, the decrease in sediment connectivity triggered by vegetation restoration was much greater than the increase induced by gully development. The results of this study help understand the change in sediment connectivity over time under the comprehensive impact of vegetation restoration and gully development at small watershed scales in semi-arid regions.