Soil salinization in the oasis areas of downstream inland rivers —Case Study: Minqin oasis

Soil salinization is the main resource and environmental problem in arid and semiarid regions, and it seriously restricts regional ecological security and sustainable agricultural development. Accurate monitoring of soil salinization and analysis of its main influencing factors are of great significance to the improvement and management of soil salinization. In this paper, the normalized difference vegetation index (NDVI) and salinity index (SI) were extracted from Landsat images of the Minqin oasis from 2000 to 2018, and these data were used to construct a soil salinization remote sensing monitoring index model (SDI). The index extracted by the model was used to monitor the soil salinization information, and the index values were graded to obtain different degrees of soil salinized land. The measured data were used to verify the accuracy of the SDI through trend analysis, stability analysis and other methods, and explore the characteristics and main influencing factors of soil salinization in the Minqin oasis. The results showed that the spatial distribution characteristics of the different degrees of soil salinity extracted by the SDI model were consistent with the measured results. The area of salinized soil in the Minqin oasis exceeded 80%, and the proportion of lightly salinized soil was the largest. The area ratio of salinized soil did not change much from 2000 to 2018, but the changes between different degrees of salinized soil were large.The unused land in the Minqin oasis exhibited a high degree of salinization, which was manifested spatially in the northwest of the Minqin oasis and the areas surrounding Qingtu Lake. In addition, the soil salinization of the Minqin oasis exhibited obvious seasonal differences, and the different degrees of salinization also changed with the change in seasons. The analysis of the main influencing factors of soil salinization in the Minqin oasis revealed that the large land occupation ratio of salinized land in the Minqin oasis was related to the local climatic factors. In recent years, changes in soil salinity in parts of the Minqin oasis and Qingtu Lake area were mainly the result of ecological water conveyance.