Study On Regional Characteristics And Evolution Law Of The Groundwater Chemical Composition In Jinghe River Irrigation Area

According to the statistics, there are 402 large-scale irrigation areas in Our country at present, though the large-scale irrigation area is 1/9 of the whole nation cultivated areas, the grain yield is 1/4 of whole country,s, the irrigation area plays an important role in producing grain,cotton and oil。The significance of the irrigation area located in the northwest is especially enormous. Jinghe river irrigation area locats in the central of the Shan xi plain plain. Jinghe River river is the water source that used in irrigating in this irrigation areas. In the recent years, the water resource of the irrigation area is short of the unified plan, the phenomen of lacking for water is very serious.In order to satisfy the agriculture irrigation,the irrigation area has to exploit the groundwater in the successive years。This leads to the decline of the groundwater level and the change of the chemical composition in time and space。So, this paper studied the regional characteristics and evolution law of the groundwater chemical composition in Jinghe river irrigation area, this can provided an important science basis for exploiting groundwater resources rationally and treating the groundwater pollution.Based on field suvrey and analysis of the groundwater chemistry data,this paper applly the hydrogeochemistry theory and Kriging method and study the regional characteristic of the chemical composition in groundwater in。The research indicates that ,the main chemical ion in groundwater in Jinghe River irrigation area is HCO3-,SO42-,Na+,Mg²⁺。From the upper reaches to the lower reaches of the irrigation area,the groundwater type transits from the HCO3-SO4-Na-Mg water to SO4-HCO3-Na-Mg water.The large amount of the ion concentrate in the lower reaches of the irrigation area.So that ,in the lower of the irrigation area ,the mineralization degree and the TDS is high than other places of the irrigation area。Besides, the contents of Cr6+ are higher ,it has already far exceeded the irrigating water standard and drinking water standard in Yan Liang district and San Yuan county.Base on the groundwater quality data of the irrigation area in 1990,the paper discussed the evolution characteristic of the ground water,s chemistry component. We find that: the area that the contents of TDS is between 2and 3 g/l has expanded obviously, the scattered distributes has spreaded into the strip belt area.The area where the concentration of SO42-,HCO3-,Na+,Ca²⁺,Mg²⁺ is high,has already expanded obviously , and the average thickness of the HCO3-,Cl-,Na+,Mg²⁺ has a growing trend in the past several years.This paper appllied the ratio of the milligram of equivalent and studied the effect that how the groundwater,s chemical composition has formed. The main reason why the content of the TDS in the lower reaches of the irrigation area is higher than other areas of the irrigation areas is that the water driving force condition such as runoff and excretion is bad,but the evaporating and dissolve filtering effect are very intensely;otherwise ,we find that the contents of TDS has correlativity with the percent of the milligram of equivalent ,and we find that the contents of TDS has minus correlativity with the percent of the HCO3-milligram of equivalent。...