Study On Soil Salinization And Groundwater Control In Irrigation Area Of Ili River Valley

Soil salinization is one of the major eco-environmental problems in arid and semi-arid agricultural lands in the world. It resulted from the effects of regional natural conditions and human activities on water-salt movement. Soil salinization is related closely to groundwater conditions. Therefore, many researchers have studied the relations between soil salinization and groundwater conditions, and have achieved some important results. But most of the studies have been concentrated mainly on the effects of groundwater depth or quality on soil salinization. Studies of the relations between soil salinization and groundwater under the co-effectivies of groundwater depth and salinity still need more specific studies.In recent years, with the improper exploitation of water and soil resources in some irrigation areas of Ili River Valley, soil salinization in the area has been gradually increased, and apparently obstructed the agricultural sustainable development. Aimed at the current situations of soil salinization in Ili River Valley, based on the theories of eco-hydrology and mathematical statistics, take groundwater as the main clue, the changes of groundwater conditions and soil salinization were studied, and the relations between groundwater conditions and soil salinization were quantitatively analyzed, the main causes of soil salinization were clarified. The ecological water table for the study area was confirmed, and the effective measures for control of soil salinization were analyzed. Results of the study could provide good scientific basic for ecological protection and sustainable use of soil, water resources in Ili River Valley. The main results of the study were as follows:1) Based on the analysis of the measurement datum from soil, groundwater and surface water, the quantitative relations between soil salinity and ion components were discussed, the characters of soil salinity under different land use types, irrigation methods and different periods were analyzed. Results showed that:46.32% of soil samples in the study area were salinized, and the main type of saline soil was sulphate saline soil. Anions were mainly SO42- and Cl- while cations were mainly Mg2+, Na+, and Ca2+ in the soil. The abundance of salinity of root zone soil layer for different land use types was in the following order:grassland> glebe field> paddy field> forest land. The abundance of salinity of root zone soil layer for different period was in the following order:before spring irrigation> summer irrigation> after autumn irrigation> during autumn irrigation. The salinity of root zone soil layer of farmlands irrigated with surface water was lower than farmlands irrigated with groundwater. Improper human activities were the main causes of soil salinization in the study area.2) The main type of groundwater was sodium chloride-sodium sulfate water. Anions were mainly SO42- and Cl- while cations were mainly Mg2+ and Ca2+ for groundwater. The abundance of groundwater salinity for different land use type was in the following order: grassland> glebe field> paddy field> forest land. The abundance of groundwater salinity for different period was in the following order:before spring irrigation> after autumn irrigation> during autumn irrigation> summer irrigation. Groundwater depth were increased from September to March in the study area, and reached to the maximum value in March, and then it declined and reached to the minimum value in June. The conception of "groundwater level active period" was put forward, and the dynamics of groundwater depth were evaluated.3) The distribution of salinity of soil and groundwater was analyzed at spatial and temporal scale. It will provide scientific basic for groundwater management and control of soil salinization. The spacio-temporal variations of salinity of soil and groundwater were essentially similar. Salinity of soil and groundwater was concentrated mainly at the central and western parts of the study area, and formed regional "salt center". In the temporal scale, the soil salinity showed maximum value before spring irrigation, and showed minimum value during autumn irrigation while the groundwater salinity showed maximum value before spring irrigation period, and showed minimum value during summer irrigation period. The trend for the changes of the salinity of soil and groundwater for each sampling lines which vertical and parallel with riverbed showed almost the same trends. It explained the close relations between the salinity of soil and groundwater. Results of factor analysis and compositor analysis explained that:groundwater salinity, EC, groundwater level, Cl" and Na+ concentration have much influence on soil salinization.4) The relationship between groundwater level and soil salinity were analyzed integrated with the analysis of the measurement of soil salinity and groundwater conditions in the study area, and adopted the logarithmic normal distribution model. The relationship models between groundwater level and soil salinity under different groundwater salinity were established. It will helpful for providing technical support for groundwater control in the study area. Results of logarithmic normal distribution model showed that:the groundwater depth should be sustained more that 2.06 m,2.49 m,2.66 m and 2.24 m for control of soil salinization while the groundwater salinity is 1-3 g/L,3-6 g/L,6-10 g/L and 1-10 g/L, respectively. The probability of the emergency of soil salinization was higher with higher groundwater salinity. According to the dynamic control of groundwater level for different periods, groundwater level might be controlled within 1.5-2.0 m during summer irrigation, and 2.0-2.5 m for autumn irrigation, before spring irrigation and after autumn irrigation. According to the results of similar researches,2.5m could be the critical groundwater depth for controlling soil salinization in arid and semi-arid zone.5) It is prior consideration to the control of soil salinization at lowlands with low salt stress in the study area. According to current status of soil salinization in the study area, the countermeasures of salt-affected soil put forward, they were much significant not only for improving the agricultural production conditions and ecological environment, but also for developing ecological, sustainable agriculture and for promoting regional sustainable development of the study area.