Effects of shallow groundwater table and salinity on soil salt dynamics in the Keriya Oasis, Northwestern China

In this paper, the spatial and temporal variability of groundwater depth and groundwater salinity associated with agricultural activities and land cover and land use (LCLU) in the Keriya Oasis, Xinjiang Uyghur Autonomous Region of China, was investigated. A decision tree classification was developed for LCLU mapping by using Landsat 8 imagery. Radial basis function, Pearson’s correlation coefficient, Moran’s I statistics and geographically weighted regression were employed to identify the spatial and temporal relationship between topsoil salinity and LCLU types. The results showed that groundwater depth in about 75 % of the study area was less than 3.0 m. Groundwater salinity showed an increasing trend with decreasing groundwater depth. A relatively higher positive correlation (r = 0.87) was found between groundwater salinity and topsoil salinity. Topsoil salinity was exacerbated by agricultural activities at the upstream of seasonal rivers, causing severe soil salinization and soil degradation in the downstream. Both groundwater depth and soil salinity showed seasonal fluctuations with the shallowest groundwater level occurring in spring, while during summer and autumn, groundwater depth increased due to the extensive of agricultural water consumption and the regional evapotranspiration, which was followed by a winter recharge; non-saline groundwater region was 21 % of the research area in spring, which dropped to 1.1, 1.0 and 1.2 %, respectively, during the summer, autumn and winter. The results also demonstrated that shallow groundwater depth of 2.5 m is the critical depth value for soil salinization in the Keriya Oasis.