## 4 Discussion  
The spatial distribution pattern of soil salinity in the study area is affected by many factors. The differences in topography, groundwater level, and groundwater properties may cause this spatial distribution pattern, and agricultural activities will accelerate the formation of this distribution pattern. The economy in the Weigan River Basin oasis is dominated by agriculture, and the traditional flood irrigation is the main irrigation method. Therefore, irrigation and drainage have an important impact on the soil salt content of the oasis. In the Weigan River Basin oasis, the Weigan River and the Yingdaya river flow through a wide area, and there are large and small irrigation channels and alkali drainage channels distributed around these two rivers (as shown in Figure 8). Therefore, taking the two rivers as the research object, 40 points are selected from the upstream to the downstream of the two rivers, and the sampling points are evenly distributed on both banks of the river. According to the sampling points and Kriging interpolation results, the distribution profile of soil salinity in the layers between 0 m and 0.2 m is drawn, and the soil salinization status in this area is analyzed. Figure 9 is the profile of total salt content of two rivers. It can be seen from the figure that the soil salt content increases with the trend of the river, showing a distribution of low in the upstream and high in the downstream. Topography is an important factor that affects the soil properties and determines its changes [36; 37]; these high salinity areas are located in the lower southeast of the study area and the edge of the oasis, as shown in Figure 10.  
Figure 8: Distribution of Weigan River Basin oasis water system. Analysis of the reasons the delta oasis in this basin undergoes less precipitation, evaporation, and soil salt accumulation shows that the salinization situation is more serious. During irrigation in the upstream region, due to the higher terrain, the salt accumulates with the water to the middle and lower reaches of the lower terrain, and the salt accumulates the most in the lower reaches of the basin and the edge of the oasis, so the soil salt content is the highest. For the Weigan River Basin oasis, soil salinization is an important reason restricting the development of local agriculture [38]. Due to the serious salinization, a large amount of water is used for salt washing in this area every year. The salt enters the alkali drainage channel and is carried into the downstream area by the alkali drainage channel, which also intensifies the formation of the salt distribution pattern in this area. At the same time, this irrigation method also leads to the rise of the water table, further aggravating the degree of salinization in the area. In a basin, groundwater and surface water are mutually replenished. Soil salinity and groundwater mineralization are related to one another; the higher the salt content, the higher the groundwater salinity [17; 35]. Therefore, in groundwater and surface water supplies, each of these factors will also affect the salinity of surface water, and an increased in the main surface water salinity of irrigation water will further aggravate the degree of salinization in this area. In the Weigan River Basin oasis, due to the local long-term irrigation mode and unreasonable methods to suppress soil secondary salinization, the oasis in this area has a tendency to expand outward, but at the same time, the degree of salinization is further deepened [13]. As can be seen from  
Figure 10: Contour map of Weigan River Basin oasis. Figure 9: Distribution profile of soil salinity in the layers between 0 m and 0.2 m of two rivers: profile of soil salinity in the layers between 0 m and 0.2 m along the Yindaya River (**a**); profile of soil salinity in the layers between 0 m and 0.2 m along the Weigan River (**b**).