Study on migration of different types water during farmland-wasteland-lake system in Hetao Irrigation District

In order to find out the migration and transformation regularity of different types of water in cultivated land-wasteland-lake system, water samples were collected from representative sampling points in the system during the typical period from 2018 to 2019. The δ¹⁸O variation characteristics of different types water in different periods were analyzed, and the contribution rate of different types of water transformation was calculated by two-terminal element mixed model and soil hydrodynamics theory. The results showed that during the irrigation period, 82% of the irrigation water was stored in 1m soil, 18% of the irrigation water recharged the groundwater of cultivated land through leakage. 76% of the irrigation water of canal system contributed to the groundwater of cultivated land through underground lateral runoff. The average contribution rate of irrigation water and rainfall to cultivated land groundwater was 94% and 6%, respectively. The average contribution rates of cultivated land groundwater and rainfall to wasteland groundwater was 71% and 29%, respectively. The average contribution rate of wasteland groundwater and rainfall to lake was 43% and 57%, respectively. The amount of water contributed by canal system irrigation water to cultivated land groundwater through underground lateral runoff was basically transferred to wasteland groundwater. The transfer and transformation of groundwater was triggered by canal system water lateral runoff. The 5^th day after irrigation, saturated-unsaturated lateral recharge existed in 0-40 cm soil layer at the junction of cultivated land and wasteland. The 15^th day and 30^th day after irrigation, groundwater of cultivated land and the junction of cultivated land and wasteland recharged soil water in 40-60 cm(root zone), 80 cm and 100 cm soil layer. The 30^th day after irrigation, the irrigation water in the cultivated land disappeared. In non-irrigation period, wasteland groundwater and lake were consumed much water. Therefore, lake should be recharged water. The calculation results were demonstrated with relevant research, which were reliable and can provide important reference for water resources analysis of cultivated land-wasteland-lake system.