Characteristics of Hydrogen and Oxygen Isotopes in Precipitation on Changwu Tableland

Precipitation is the most important component of water cycle process.Hydrogen and oxygen iso- topic compositions of precipitation are closely related to the source of vapor and the meteorologic process of rainfall formation.The isotopic compositions of precipitation over the Changwu tableland in 2005 are stud- ied.Local meteoric water line is fitted asδD=7.44δ~(18)O+1.69.Its slope and intercept are lower than those of global meteoric water line and Chinese meteoric water line,which are related to the geographical and mete- orological characteristics in the area.Deuterium excess shows seasonal variation.The values of deuterium excess are higher than or about 10 from April to June and less than 10 from July to October.Both tempera- ture and rainfall amount have no significant effect on the isotopic compositions of individual rainfall events with one-day-period.For the 2-day-period rainfall events,rainfall amount have significant effect on them. Moreover,the isotopic compositions of precipitation have seasonal variation.TheδD andδ~(18) O values are higher in spring,lower in summer,and much lower in autumn,which is more remarkable in the average ofδD andδ~(18) O when the individual rainfall amount is assigned as a weight.