The Cause Of Groundwater Salinization And Paleoclimate Characteristics In Yanchi Area Of Jiuquan East Basin

Yanchi area of Jiuquan East Basin in Gansu Province is the largest enrichment area in mirabilite and raw salt, it is also the main groundwater distributed area in Jiuquan East Basin. Therefore, it is very useful to make research on the cause and law of groundwater salinization. On one hand, it is helpful to make clear of water and salt migration, enrichment and mineralization of salt in arid area groundwater system. On the other hand, it is significant to reasonable development and utilization of salt mines in northwest inland.In order to provide logical reasons for sustainable utilization of groundwater and rational exploration of salt mines, the goal of this study is to reveal the cause and evolution characteristics of groundwater salinization in Yanchi area of Jiuquan East Basin. Therefore, Jiuquan East Basin as the study area and YanChi as the main study area, the study focused on the following four main parts: (1) water chemistry and environmental isotope characteristics of different water body in water cycle systems; (2) changing law and source of groundwater salinization; (3) paleoclimate significance during the process of groundwater salinization.Based on water cycle system theory , environmental isotope and water chemistry information, this study comprehensively used hydrogeology, hydro-geochemistry, isotope hydrology, and related mathematical theory, it also combined qualitative estimation and quantitative analysis. Using these methods, this study maked clear of natural background condition of the study area, and analyzed water chemistry and environmental isotope characteristics of different water bodies by the technologies of tracing function and radioactive dating techniques of isotope and water chemistry information, and illustrated evolution characteristics and source of groundwater salinization. Based on the above analyses and combining paleoclimate index of pollen and chlorine isotope, this dissertation discussed paleoclimate and environment change in the last 16 thousand years. Finally, the peper gained following understanding.1. Relationship between groundwater salinization evolution history and modern water cycleA lot of groundwater chemistry and isotopic information showed that groundwater salinization of Yanchi area of Jiuquan East Basin happened in aBP history, and there is a close relationship between groundwater salinization and modern water cycle. Major source of groundwater salinization is from precipitation infiltration recharge, Qilian Mountain area river leakage, and deep groundwater leaky.2. Cause of groundwater salinizationYanchi is the water and salt enrichment area in water cycle system of Jiuquan East Basin, because there are several advantages, such as adequate supplies of water and salt, geological and geomorphological condition of gathering water and salt (Yanchi valley and Beishan obstruct), suitable water cycle condition of accumulating water and salt (stagnant runoff and vertical evaporation), and good climate condition of concentrating salt (perennial drought and strong evaporation intensity). All the conditions are conductive to groundwater salinization.3. Paleoclimate evolution characteristics in the last 1.6 million yearsThere was a climate evolution process from cold-drying to wetness to drying in Yanchi area in the last 1.6 million years. During the process, grassland was becoming drought, lakes were drying, water salinization was starting, and woody plants and pteridophyte were almost disappeared. Instead, drought-resistant plants were becoming more, so fleabane and goosefoot were becoming modern landscape and groundwater salinization was finally formed.4. Project of logical utilization of groundwaterAccording to water and salt migration and distributing characteristics, this study divided the whole study area into three groundwater utilization parts. They were piedmont groundwater conservation area, middle oasis exploration area and northern salt mines groundwater protected-mining area. Considering both exploration and recovering, the utilization programs of groundwater can not only ensure salt mines mineral production, but also guarantee rational utilization of water resources.