Isotopic Variations Of Surface Water In Typical Water-receiving Areas Of The Middle Route Of South-to-North Water Diversion Proiect

China's South-to-North Water Diversion Project(SNWDP),the largest inter-basin water transfer project in the world,changes the natural distribution pattern of water resources,thus affecting the regional water cycling.Under such engineernng background,however,few studies have revealed the water loss from open transfer canal and the impact of inter-basin water diversion project on hydrological process in water-receiving areas.Taking the middle route of SNWDP as a case,this paper explores the hydrological processes in the typical water-receiving areas using stable water isotopes.In addition,it is difficult to estimate the evaporative loss from rivers.Giving the relative simple hydrological setting,the SNWDP canal provides an ideal place to study this process.With these objectives,this paper collected water samples and analyzed their isotopic compositions from the SNWDP canal and its typical water-receiving areas.The evaporation loss ratio in water transfer canal is estimated by using stable isotope method.In addition,spatial distribution characteristics and influencing factors of surface water isotopes in typical water-receiving areas are analyzed.Preliminary results and conclusions are:Evaporation and precipitation are the main factors affecting the spatial variations of hydrogen and oxygen isotopes in canal water.Evaporation makes the values of ?18O and?2H of the canal water generally increase from south to north,while the precipitation on the canal surface causes the opposite change.Based on the model of water balance and stable isotope mass balance,the evaporation loss ratio in water transfer canal is estimated.It is found that the evaporation loss ratio in the north reach is stronger than that in the south,and the evaporation loss ratio in the whole canal is between 1.7%~1.9%.There are clear spatial differences in surface water isotope composition between Shaying River(a tributary of the upper reaches of Huaihe River Basin)and Haihe River Basin.River water 8 80 values in the Shaying River and Haihe River basins are-6.5‰and-7.2‰ reflecting the latitude effect in precipitation isotopes.While d-excess values in the two basins are 4.1‰ and 2.6‰,indicating stronger evaporation in the Haihe River basin.Further,isotopic signals of canal water have been found in some rivers.which indicates that inter-basin water diversion has an impact on river water isotopes.For instance,the Yongding River water ?18O value in the upper Haihe River basin is-5.9‰.While downstream of the water-receiving point,?18O decreases to-7.9‰ which is in between the Yongding River and canal water ?18O values(-8.1‰)fingerprinting the transferred water signals in the water-receiving areas.The results from this study provide isotopic evidence of the influence of inter-basin water diversion on regional water cycle and preliminary attempts to study the interaction between human activity and water cycle using stable water isotope techniques.