Variations in groundwater levels and salinity in the Ili River Irrigation Area, Xinjiang, northwest China: a geostatistical approach

Groundwater levels and salinity are significant contributors to soil salinisation in irrigated areas. In this study, spatial and temporal variations of groundwater levels and salinity in the Ili River Irrigation Area in the western arid zone of China were analysed using a geostatistical approach. Results showed that: (1) groundwater salinity varied widely, with a maximum of 30.70g/L and minimum of 0.20g/L, while maximum groundwater level was 31.10m and minimum was 0.54m. The abundance of major ions in groundwater was in the order: Cl-SO42-Ca2+Mg2+K+Na+CO32-=HCO3-. Groundwater salinity had a good positive correlation with EC, Cl-, Na+, HCO3- and Mg2+ (correlation coefficient 0.90); (2) a Gaussian model was the most suitable semivariogram model to describe groundwater levels for four measurement periods, while a Spherical model was most suitable semivariogram model to describe groundwater salinity in March, September and November, and an Exponential model was most suitable variogram model for June. RA relatively strong spatial and temporal structure existed for groundwater levels and salinity due to very low nugget effects. The nugget-to-sill ratio indicated that groundwater levels and salinity in the study area have relatively strong spatial dependence. The groundwater levels and salinity showed an east-west, north-south U-shaped distribution in each measurement period; (3) maps of kriged groundwater levels and salinity showed that deeper groundwater was found in southern parts, with more shallow groundwater in northern parts of the study area. Higher groundwater salinity was found in central parts, with lower salinity in marginal parts of the study area. It is clear that substantial soil salinisation has taken place in central parts of the study area, and more attention should be paid to these areas to prevent future problems.