Study On The Groundwater Chemistry Evolution Of Nuomuhong Area In Qinghai Province

Water is the most valuable natural resources in the arid northwest inland basin of ourcountry. The research of groundwater chemistry characteristics and evolution is not only thebasis of water resource appreciation and development，but also an mportant approach torecognize the formation and circulating of groundwater。This paper takes the representative Nuomuhong area in the Chaidam Basin as study area,takes groundwater system theory for guidance, based on geohydrology survey and watersampling, synthetically adopting the theory of geohydrology, hydrogeochemistry,isotop-hydrology and so on, as well as adopting methods of integration of qualitativejudgement and quantitative analysis, carrys out groundwater chemistry and evolution inNuomuhong area.Main achievement and cognition getting as follows:1. The groundwater chemical distribution relates closely to the phreatic flow field and hasclear zonational characteristics,reveals the circulating law of recharge-runoff-drain. Fromnorth to south, along facing border direction, the chemistry type and TDS of groundwaterwater have regularly changes. On the top of proluvial fan, the main chemical effect of shallowwater is eluviation, that the water chemistry type is HCO3·SO4·Cl-Na·Mg·Ca, TDS＜1g/L,fresh water, showing the characteristic of supply area. In the middle of the proluvial fan, themain chemical effect of shallow water is leaching effect and evaporation concentrating effect.The main water chemistry type is SO4·Cl-Na and the TDS of the shallow water increases from1g/L till10g/L, showing the character of runoff area. In the salt marsh zone, the mainchemical effect of shallow water is evaporation concentrating and mixing effect. The mainwater chemistry type is Cl-Na, TDS increasing more than10degree, which the maximumamount is302g/L, forming high salt water, brine, showing the characteristic of dischargearea.2. The curve of δD and δ18O shows that the groundwater main comes from the supply ofriver in the study area. The calculation of CFCs and3H indicates that the groundwater ismixed from river and old water. With the increasing of depth, the proportion of groundwaterreceiving the river is decreasing. Along the direction of groundwater runoff, the age of14C isgrowing.3. The simulation result of water-rock model indicates: leaching, evaporation inspissation,alternative adsorbing of positive ion and mixing is the main effect of the chemical water formation in the Nuomuhong in Qinghai. Along the direction of Nuomuhong river, it mainhave the depositing of calcite and dolomite, resolving of gypsum and potassium feldspar,adsorbing of Ca-Na alternative positive ion and resolving of halite or plagioclase.4. Based on the characteristics of hydrogeololgy condition, groundwater chemistry andisotope, we have built circulating groundwater pattern on typical section and divided it intotwo types, local and regional type.