| Groundwater is the dominant water supply source in Hohhot city,which plays an important role in guaranteeing the water consumption of urban and rural residents,supporting social and economic development and maintaining ecological balance.The sedimentary environment of the late pleistoceneholocene strata in Hohhot basin was mainly controlled by the local Dahei river,and the influence of Yellow River was small.Therefore,the formation mechanism of shallow high arsenic water is very typical.There is a large area of high arsenic shallow groundwater in Hohhot Basin.Tumert Left Banner and Toquetto County in 13 drinking-water type endemic arsenism counties of Inner Mongolia Autonomous region are located in the study area.The research on this aspect is of great realistic and scientific significance to the water supply safety and formation mechanism of high arsenic shallow groundwater in Hohhot Basin.This paper took shallow groundwater as the research object,carrying out a large number of field investigations,sample collection and testing,data analysis on the basis of the detailed geological,hydrogeological data accumulated in the past.The main research contents,methods,and conclusions were as follows:?Hydrochemical characteristics of regional groundwater.The dominant and non-dominant ionic hydrochemical types were divided according to whether the milligram equivalent percentage of the major ions was more than 50%.The distribution of the cation hydrochemical types showed strong horizontal zoning from the groundwater recharge area of the east of alluvial-lacustrine plain and north mountain front alluvial-pluvial sloping plain to the discharge area of the central and west of Dahei River alluvial-lacustrine plain.The bicarbonate dominant type groundwater was widely distributed in the study area,which is the main type of the anion hydrochemical types.The Formation mechanism of the bicarbonate dominant type was different in different regions;?Distribution of high arsenic shallow groundwater.The high arsenic shallow groundwater mainly distributed in the west-central part of Dahei River alluvial-lacustrine plain,and the two sides of Dahei River in the west-central part of the Dahei River alluvial-lacustrine plain were the areas with the most densely distributed of high arsenic shallow groundwater and the highest arsenic concentration.The Indicator Kriging method showed that the probability of occurrence of high arsenic shallow groundwater in the west-central of Dahei River alluvial-lacustrine plain was more than 0.5;?Hydrochemical characteristics of high arsenic shallow groundwater.High arsenic shallow groundwater mostly belonged to soda water,and its formation was influenced by cationic exchange,redox reaction of organic matter decomposition,such as desulfurization according to various ion ratios.The distribution of inorganic arsenic was significantly influenced by ORP.EDTA solution had a good protective effect on groundwater inorganci arsenic speciation samples.?Characteristics of chemical evolution of sediment and groundwater in typical section.Iron and manganese were more strongly correlated with arsenic in different depth sediments of high arsenic groundwater point and were more weakly correlated with arsenic on low arsenic groundwater point.There was no significant difference in the content of arsenic,iron,manganese and sulphur in sediments of high and low arsenic groundwater points,but larger difference in groundwater.Redox condition was the main control factor of arsenic concentration in groundwater.?The enrichment mechanism of arsenic in shallow groundwater.The lacustrine sedimentary environment during the late Pleistocene to Holocene had an important influence on the formation and distribution of high arsenic shallow groundwater.The reducing dissolution of iron and manganese oxides and alkaline desorption were the prerequisites for the formation of high arsenic shallow groundwater.Slow runoff provided important hydrodynamic conditions for arsenic enrichment in groundwater. |
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