Changes of δ18O and δD along the Dousitu River, Inner Mongolia, China, and their evidence of river water evaporation

On the basis of the hydrogeology of the Dousitu River drainage basin, the changes of water flow rate, delta O-18 and delta D along the Dousitu River are discussed according to measured and analytical results. Changes of flow rate along the Dousitu River agree well with groundwater level contours and the recharge and discharge of groundwater to the river. When compared with other types of water in the area, it is obvious that the O-18 and D of river waters have experienced evaporation. The changes of delta O-8 and delta D along the Dousitu River are mainly caused by combined effects of groundwater recharge and river water evaporation. The recharge of groundwater makes delta O-18 and delta D of the river water decrease. Evaporation makes delta O-18 and delta D of the river water increase. The evaporation fractions of the river water are calculated using the kinetic fractionation theory. Results showed as much as 10-30% of water was evaporated in different segments of Dousitu River.