Hydrochemical Characteristics And Formation Mechanism Of Shallow Groundwater With High Iodine In The Weinan Region

The iodine content of drinking water is very important to the health of the local residents.Iodine deficiency and high iodine can cause diseases such as goiter.At present,there are many studies on iodine deficiency at home and abroad.And the implementation of"universal iodization"in China has basically solved the problem of iodine deficiency in our country,but the research on high iodine problem is relatively few.Compared with iodine deficiency,the problem of excess iodine in groundwater is difficult to solve.In this paper,the Weinan section is selected as the research area.The problem of groundwater high iodine is studied by collecting data,field investigation and visiting,sampling analysis and testing,test results analysis and so on,then the following conclusions are drawn:（1）The groundwater component content distribution is generally high in the middle and lower in marginal areas,the pH value is weak alkaline/alkaline on the whole,the central region in the study area,the formation of a high water TDS.The hydrochemical type is mainly HCO_3-Ca·Mg and HCO3-Mg·Ca type in the alluvial fan area in the front of the mountain.In the loess tableland area,they are mainly HCO_3-Na and HCO₃·SO_4-Na·Ca.In the middle alluvial plain area,they are mainly Cl·SO_4-Na·Mg,SO₄·Cl-Na·Mg and Cl·SO_4-Na,but in the Weihe River and Luohe River valley,the main are HCO_3-Na-Mg、HCO₃·SO_4-Na·Mg、HCO₃·SO_4-Ca and SO₄·Cl-Na.（2）The high iodine groundwater in the study area is mainly distributed in the central and western regions of the study area,that is,the surrounding areas of Fuping and Pucheng,and the distribution of high iodine groundwater around the East Dali in the eastern part of the study area.The iodine content in the water samples collected over the whole study area is more than 150 mg/L,which accounts for 72%of the total water samples,and the highest iodine content is more than 28mg/L.Vertically,the groundwater of high iodine is more widely distributed in the groundwater environment less than 50 meters,and the groundwater environment of more than 50 meters is relatively less.The hydrochemical type of the groundwater in the study area is mainly SO₄·Cl-Na·Mg,HCO₃-Na·Mgand HCO₃-Na。（3）The isotopic characteristics of the study area are basically consistent with the topography and hydrogeological conditions in the study area.From the results of the isotopic test and analysis,the age of high iodine groundwater in the groundwater is mainly between2000-5000 years,which is formed in the Quaternary period.The formation conditions of the high iodine groundwater in the study area are mainly confined to the groundwater system.In addition,the high iodine groundwater in the study area is strongly influenced by evaporation.（4）The correlation analysis and principal component analysis of the chemical components and iodine content of groundwater can be seen that the groundwater is mainly influenced by weathering and leaching in the area of the alluvial fan in the northern front of the mountain,and there is a clear positive correlation between the ions of the groundwater.The groundwater environment is more complex in the loess tableland area and alluvial plain area.It is mainly affected by the dissolution of magnesium salt and silicate,the decomposition of microorganism on organic matter and the effect of agricultural fertilization.In the Weihe River and Luohe River valley,the groundwater is mainly influenced by the dissolution of magnesium salt and the activities of agricultural fertilization,and it is influenced by evaporation and organic matter decomposition.（5）The Phreeqc software is used to calculate the SI index of the water in the area,and the groundwater evolution process is simulated in reverse direction along the runoff direction.The results of the analysis of hydrochemistry,isotopes and hydrogeochemical effects can be seen that the formation of high iodine groundwater in the study area is controlled by many conditions.The iodine in the sediments is the main source of iodine in the groundwater.The filtration of the sediments is the main factor in the formation of high iodine groundwater in the study area.In addition,the reductive conditions of the closed groundwater environment in the central and western regions,the decomposition of microorganism on the organic matter and the relatively small hydraulic gradient are both the promotion of the release of iodine in the groundwater and the release of iodine in the groundwater.The factors affecting the enrichment are the leaching of the vertical alternation of the eastern Luohe River and the strong evaporation.