The Analysis Of Water Environment Changes Over The Past 30 Years In The CaoWoTan Basin Of Jingtai Irrigation District

Four hundred and two large-sized irrigation districts, each has an area over 2×10⁴hm², occupy 1/9 of the cultivated land, and produce near upon 1/4 of the food, cotton and oil in China. The arid irrigation districts, which are in the northwest of the country, take on a greater significance for the local human society. Because the artificial actions strongly changed the courses of the water cycle, the local water environment, soil environment and other environments were changed, and it has produced huge influences for socioeconomic developments of the region. Compared with the studies of the rational use of water resources, there are fewer studies for the evolvement of the water environment in the arid irrigation districts;it lacks systemic research for the water environment changes from the complete irrigation course.In arid irrigation districts of northwest of China, because of its special climatic conditions, water evaporates strongly. If it isn't managed well, secondary salinization of soil is easy to be brought, and a series of problems in rational use of water resources may occur, sometimes the investment for the irrigation districts is unable to make ends meet, but Jingtai irrigation district is one of the fewer which can be operated well in the long-term irrigation.Based on the existing research, this thesis regards the Caowotan basin of Jingtai irrigation district as its study subject, analyzed the changing characteristic of water environment and salinity in soil in recent 30 years. The result showed that the quantity of ground water and water table had a persistent ascending process, and this has kept stably. As a whole, the degree of mineralization had a ascend trend, there was a biggish value in 1988, then the trend changed to smooth, and now the value is some bigger. The content of SO₄^2- augmented at the beginning, and then descended, it has held stable. The contents of Cl^- and Na⁺ were growing slowly, Ca²⁺ and Mg²⁺ were maintaining stable. In the soluble salt of the soil, the concentration of Cl^- and Na⁺ are reducing, and the quality of soil tends to becoming good. The thesis also discusses the changing causes of the water environment and salinity in soil, and brings forwardmany measures and advices for the rational usage of water resource and water environment protection.