Study On The Water Chemical Characteristics In Zhabuye Salt Lake, Tibet

Salt Lake is a kind of extremely valuable natural resources, which formed in special geological environmental conditions, with solid and liquid coexisting. There are a variety of mineral salts, which provide a wide range of raw materials for various humans industries. The analysis of the dynamic changes in water chemistry in salt lake area has great significance for environmental protection and resource exploitation.In this paper, Zhabuye Salt Lake was regarded as the research object. Based on the collected meteorological hydrological data and the data of landform, geology and the salt production, the hydrogeological condition was analyzed. The temporal and spatial variation characteristics of water chemistry were researched. Through the analysis of the characteristics of salt lake source sink term, the causes of the changes in water chemical compositions were explored. Water hydrogeochemical evolution of the salt lake was analyzed and the numerical simulation method was used to study the migration of groundwater and salt, and the change trends were predicted, Based on the above research, the following main conclusions have been drawn.(1) Spatiotemporal variations characteristics of hydrochemistry composition: On the temporal scale, from May to September, salinity value was great, with the highest salinity in July. The salinity in the north lake was between 440 ~ 450 g/L, and in the south was between300 ~ 410 g/L. During this period, the change range of salinity was large, first rose then reduced. From November to April of the following year, salinity value was small. The salinity in the north lake was between 350 ~ 370 g/L, and in the south was between 80 ~ 100 g/L.Salinity was stable during this period and the change was small. The average inter-annual variation of salinity in the salt lake first increased, then decreased and then increased, trough appeared in 1993. On the spatial scale, salinity of the salt lake on the horizontal distribution,from the edge to the center, salinity became larger gradually, the salinity was much smaller near the place having fresh water supply than that away from the recharge area. On the vertical distribution, with the increasing of depth, the salinity was increasing gradually.(2) Evaporation and chemical composition characteristics of supply source water:Evaporation was the only way of discharge in the salt lake. The amount of evaporation was large every year and the average was about 2500 mm. The fluctuation of annual evaporation was small and the high intensity of evaporation was an essential factor for the formation of the salt lake. The fluctuation between different months was very obvious. The maximumevaporation was in June and July and the amount of evaporation was nearly 350 mm per month, and the minimum was in January and February and the amount was nearly 75 mm per month. The precipitation in the salt lake was small and the proportion of the amount of chemical minerals contained in precipitation was relatively stable. The salinity was between0.03 to 0.29 g/L. The minimum value was only about 80 mm and the maximum value was only 300 mm. Annual average value was about 120 mm. Precipitation mainly concentrated in July to September. The average salinity in rivers was only 0.542 g/L. Groundwater finally recharged the salt lake in the form of springs. Salinity is between 0.5 to 0.6 g/L.(3) The migration rule of water and salt in groundwater and the prediction of evolution trend: In the near future, if the hydrometeorological conditions do not have big fluctuation,the content of salt in the place will not have much change either. The level of unconfined aquifer will increase, while the level of confined aquifer will reduce. The reason is there being a process that confined aquifer recharges unconfined aquifer, which makes the salt concentration decrease in the unconfined aquifer, while that in confined aquifer have little change. But according to the natural geographical environment, in the long evolution process of the lakes, the water level of the lake will reduce and the salinity will increase.