The Calculation And Simulation Of Hydro-geochemistry In Small Watershed Of Nyingchi

Yangzi river basin is the representative river basin to study substance migration and balance; it derives from the east of Qinghai-Tibet Plateau. Qinghai-Tibet Plateau provides an ideal natural testing ground to study the natural environmental impact under global climate change for its irreplaceable geographic location and particular science meaning.The theories of substance circulation and geochemical balance were applied in this thesis. It studies the relationship of precipitation in small watershed of Nyingchi and chemical composition of river water in the basis of prior research achievements, and the contribution of groundwater to chemical composition of river water was determined in this thesis.The study includes hydrological dynamics (precipitation, surface water and groundwater), water chemistry and substance balance models, water-rock interaction and change. The importance points is to study the mutually transformation of precipitation, surface water and groundwater in the process of geochemical balance and substance migration. The research could not only cover the shortage for just considering the contribution of surface water during the river erosion, but also could consummate the relationship of substance balance for river erosion. Meanwhile, the research provides precondition for further studying about contribution of atmospheric dry deposition to chemical composition of river water, and will offer basic data to study global climate change impact on environment.The study area is the small watershed in source region of Yangzi River in Nyingchi, Tibet. It is a watershed with simplex lithology of granite and without human activities influence; it has good condition for research.Natural outcrops of spring and artificial wells were utilized in the research to collect surface water and groundwater samples periodically in difference season under natural condition, all the water samples testing were conducted in National Open Laboratory to analysis the chemical composition of river water and groundwater, the test data were comparative analyzed and analyzed for basic law of logic. The contribution of precipitation to chemical composition in river water was calculated through serials of formula, and water-rock interaction simulation model PREEQC was applied to study the mineral migration and evolution characteristics of groundwater.It is indicated in this thesis, precipitation is the main recharge source for chemical composition in river water, and the process of groundwater erosion could be analyzed quantitatively utilizing water-rock interaction geochemical modeling in small watershed, it could provide strong evidence and data for mutual transformation between surface water and groundwater. The study of hydrological cycle in source region of Nyingchi could provide background data and theoretical basis for protecting the ecological environment in river source region. As a part and parcel of substance cyclic process and geochemical balance, groundwater plays an important role in the study of river erosion. The study will provide theoretical basis for substance migration in further research in the region of Yangzi River estuary.