Using Stable Hydrogen And Oxygen Isotope To Research The Conversion Relationship Of Surface Water And Groundwater In Manas River Basin

Manas river catchment is the core of economic development area in the north part of Tianshan Mountain in Xinjiang, and located in the northwest arid region of China, under dry climate condition with scarce rainfall and strong evaporation, water resource in river basin distributed unevenly in time and space. On the other hand, with the rapid development of economic society in river basin, the imbalance between demand and supply are becoming critical due to water demand increasing year after year, created a series of ecological environment problems, such as river blanking, vegetation degradation and soil-salinization and so on. Water resources problems have become a key factor restricting the sustainable regional economic development, and effective evaluation of water cycle process in river basin is precondition to solve such problems. Therefore, this thesis mainly used hydrogen and oxygen stable isotopes and radioisotope tracer technique, analyzing the conversion relationship between surface water and groundwater, the research results provide important significance for reasonable water resources planning and ecological environment protection in river basin. The main results of this study are as follows:(1) Through analyzing the compositional features of δ2H and δ18O in precipitation, surface water, groundwater and soil water, and establish the local meteoric water line and other evaporation linear equation to determine the relationship among them, at the same time, analyzing the spatial and temporal variations of δ2H and δ18O in each water body, and determine influencing factors for them, further to clarify the relationship between the recharge and discharge of groundwater.(2) Based on the values of tritium(3H)in different periods of precipitation and used the model to calculate the groundwater age. The results show that the tritium values of groundwater gradually reduced from the mountains to the alluvial plain, such as the groundwater age increased gradually from south to north, consistent with the direction that simulation of the groundwater flow field, in addition, the aquifer conditions of groundwater runoff along the river direction gradually become poor. The results show that the groundwater in the middle and upper reaches mainly from the modern water infiltration on the high altitude area, and the groundwater in downstream mainly from pre-modern water from high altitude area or most part is pre-modern water when mixing with modern water is considered.(3) Based on the stable isotope and hydrogeological conditions and used IsoSource software to realize the calculation of multivariate mixed model, qualitative and quantitative analysis of the conversion relationship between surface water and groundwater in the Manas river basin. The results showed that water resource in river basin mainly from atmospheric precipitation in the mountains, such as the 55.0% ~ 68.0% of surface water come from the atmospheric precipitation in upstream, the rest come from groundwater. In the aspect of groundwater resources, the shallow groundwater mainly from the leakage recharge of river and canal system and lateral recharge in piedmont, only the 4.0% ~ 18.0% of precipitation directly infiltration recharge it. The deep groundwater mainly from the vertical and lateral supplies of groundwater, and the surface water and rainfall infiltration is very weak.(4) Surface water and groundwater from southern mountains to the northern plains mainly experienced three different conversion processes. First of all, atmospheric precipitation collected at river water in the mountains and turned into groundwater by infiltration; River water continued to recharge groundwater in the form of channel leakage in alluvial-proluvial fan in downstream, when the river water reached the overflow zone of alluvial-proluvial fan, groundwater turned into river water in the form of springs overflow; In the alluvial plain is located in the north of alluvial-proluvial fan, groundwater is recharged directly by river water through farmland irrigation, after the rest of the river and canal water is gradually consumed under the influence of evaporation and human activity. In general, under the dual effects of human activities and natural environment changing, the conversion relationship between surface water and groundwater become very complicated in river basin.The research results provide important reference for the rational planning of water resources in river basin, which has important theoretical and practical significance for studying the mutual conversion rules between the surface water and groundwater in typical arid inland river basin in China.