Long-term impacts of ecosystem restoration on saturated hydraulic conductivity in the Loess Plateau

Abstract

Since 1999, large-scale ecological restoration activities have been launched across China’s Loess Plateau, known as the ‘Grain for Green Program’, which has substantially changed the landscape as well as the physicochemical properties of soil, including saturated hydraulic conductivity (Ks), an essential parameter in hydrological cycle. This could also contribute to the reduction of water and sediment in the Yellow River in this century. However, there is little study about the changes in root zone (upper one meter) Ks profiles at large scale. Quantitative description of the revegetation impacts on Ks is needed to assess the impacts of revegetation on local water cycle. In this research, 2665 soil samples at six depths within root zone (0–10, 10–20, 20–30, 30–50, 50–70, 70–100 cm) from four land use types (forestland, shrubland, grassland, and sparse grassland) at 25 different sites across the central Loess Plateau were collected and analyzed. Our results suggest that revegetation has significantly improved Ks values with the largest increment in the near surface layers, enlarging the vertical heterogeneity of Ks. The parameters of vertical profiles of Ks were correlated to vegetation index (NDVI), especially for Ks and its decay rate at surface, and the correlations under well vegetated land use types collapsed on the same line. The change of Ks due to revegetation was also correlated to the change of NDVI. This contrasting Ks amplified by revegetation could lead to a shift of runoff generation mechanism in the Loess Plateau. Our results could provide support for estimation of local water usage and availability changes caused by revegetation, shedding light on the vegetation restoration implementation in the Loess Plateau.