Discussion On The Relationship Between Wetland Change And The Distribution Of Arsenic In Groundwater In Hetao Basin

The Hetao Basin in Inner Mongolia is the typical endemic arsenic poisoning area, with tens of thousands of people facing risks of arsenicosis related to digesting of high As groundwater. Understanding spatial distribution of high arsenic groundwater and factors affecting the formation of high arsenic groundwater, is of practical significance of prevention of endemic arsenic poisoning.Based on field investigation, laboratory analysis, and literature research, groundwater chemistry and arsenic concentrations in the Hetao Basin were obtained. In order to evaluate the changes of the wetland in the Hetao Basin, remote sensing technology was used to extract information from remote sensing images in the past forty years, and the causes of wetland change was analyzed. The relationship between the changes of wetlands and spatial distribution of high arsenic groundwater helped to reveal effect of wetland change on high arsenic groundwater. In this paper, main conclusions have been drawn as follows.(1) High arsenic groundwater is mainly distributed in the reducing environment, which is similar to high arsenic groundwater in Southeast Asia. There is no significant relationship between As concentration and TDS. High arsenic groundwater were mostly weakly alkaline.(2) High arsenic groundwater was mostly distributed in the north and east of the Basin. Locally, high arsenic groundwater mainly occurred in the groundwater discharge areas, including the Piedmont fronts, Wuliangsuhai and Muyanghai regions.(3) Spatial distribution of wetlands changed greatly during the period from 1973 to 2014. In groundwater irrigation areas, wetlands shrank. Wetlands in Yellow River irrigated areas changed irregularly. Wuliangsuhai Lake wetland increased.(4) Climate change and human activities on water resources distribution were the major factors causing wetland change. Human activities(irrigation channels and drainage channels) are the direct driving factors that cause the change of Wuliangsuhai wetland. Rainfall is one of the major reasons that lead to the change of wetlands in Yellow River irrigation areas. Reduction of wetlands in groundwater irrigation area was related to the increase in annual average evaporation and groundwater exploitation.(5) The spatial change wetlands was generally consistent with spatial distribution of shallow high arsenic groundwater. It was shown that the increase of wetland led to high arsenic groundwater formation. The newly formed wetland areas had relatively low terrain, which favored water accumulation and deposition of organic carbon. After groundwater pumping for irrigation, the organic matter derived from the surface water and the bottom sediments was brought to the shallow aquifers, which caused the reductive dissolution Fe(III) oxides and As arsenic and therefore the formation of high arsenic groundwater.