Change Of Wet-land Distribution And Its Impacts On Arsenic Distribution In Shallow Groundwater From The Yinchuan Plain

High arsenic groundwater has long affected the life of local residents in the Yinchuan plain,since 1995 when patients with arsenic poisoning were observed.It is crucial to investigate distribution characteristics and controlling factors of high arsenic groundwater in the Yinchuan plain for preventing and controlling arsenic poisoning from groundwater.Based on spatial distribution of groundwater arsenic and the characteristics of wetland evolution and controlling factors,effects of wetland distribution and evolution on shallow high arsenic groundwater are evaluated in the Yinchuan plain.The conclusions are shown as follows.(1)The area of shallow groundwater with arsenic concentrations>10?g/L is about 2370.47 km~2 in the Yinchuan plain,which is mainly distributed in the northern part of the plain,including Pingluo County,southwest corner and central part of Shizuishan City,middle and eastern part of Helan county.In the eastern region of Yinchuan City,northeast area of Yongning County and Lingwu City,groundwater As mostly ranges between 10 and 30?g/L.(2)The wetland area of Yinchuan plain generally shows an increasing trend with exception of the years 1980 and 1996.After 1996,the increasing trend of wetland area is obvious.The spatial distribution of wetland in the plain changes greatly.The large area wetland patches increase obviously with clear outline,and the small area patches also have the increasing trend.(3)There is a positive correlation between precipitation and wetland before2000,and temperature change has little effect on wetland.After 2000,the impact of human activities on wetland changes in Yinchuan plain is more obvious.Climate is no longer the dominant factor in the evolution of wetlands in the Yinchuan plain.(4)The existence time of wetlands is an indicator of the distribution of shallow high arsenic groundwater,with the longer existence of wetlands,the greater probability of occurrence of high arsenic groundwater in shallow aquifers.When the existence time of wetland in the Yinchuan plain is greater than 19 years,the probability of high arsenic groundwater is around 100%.The existence of wetlands may lead to a change in the redox environment of the groundwater,thus affecting the release and enrichment of arsenic.