| Owing to particular topographic features—mountains alternating with basins in thenorthwest desertification area of China, groundwater is quite plentiful in desertification basinsthat are surrounded by lofty mountains and steep hills, which is favor of agriculture andanimal husbandry, as well as people residence there. While the complexity of groundwatersystem under arid climate leads to groundwater of fluorine ion and salinity accumulation.Thus fluorosis has been the most epidemic and the most dangerous endemic disease innorthwestern desertification basins.Study area is in Jilantai Desertification Basin, in the southeastern of Alashan Plateau,Inner Mongolia. The Jilantai Basin is divided into three groundwater environmental districts,including Wulanbu he shamo pasturing district, Chahaertan desert oasis agricultural districtand Jilantai saline industrial district. On the basis of Environmental Hydrogeology,Hydrogeochemistry, Environment Engineering and Geographic Information Science, ourstudy is to explore the environmental evolution of groundwater, enrichment, migration andbehavior characteristics of florine and its relevant risk assessment for environmental healthyin Jilantai Desertification Basin by field investigation, tests in both the field and laboratory.According to the theory of frozen dropping fluorine on the basis of Ice CrystallizationKinetics, frozen tests were adopted in our study to explore the influence of frozen temperatureand frozen time upon the degree of dropping fluorine as well as desalination for hypersalinityand hyperfluorine. Facilities for frozen dropping fluorine specialized for the northwesterndesertification districts were also designed in our study by automation control technique inorder to solve some significant scientific issues, including geochemistry theory ofhyperfluorine groundwater and techniques for dropping fluorine. Our research will provide atheoretical basis for scientifically using water, protecting and improving the quality of water,and provide reference for environmental evolution research other places in northeasterndesertification areas. Research results can be summarized as following:Firstly, Jilantai Desertification Basin in Alashan is a garben basin trending from northeastto southwest, whose groundwater is composed of four sub-systems: bedrock mountains,inclined piedmont plain, paleolacustrine plain and desert. Groundwater in Jilantai Basin flowsfrom basin’s edge to its central, which is mainly derived from, Rainfall, snow melt fromHelan Moutain, Bayinwula Mountain and Zhuoertaotai and runoff from the Yellow River.Some of the Quaternary confined groundwater leak to its overlying unconfined aquifer.Groundwater overdraft should be considered as the main reason for well environmental degradation of industry in Jilantai County and for agriculture in Chahaertan.Secondly, the mechanism characteristics of groundwater in Jilantai Desertification Basinare as following: the unconfined groundwater tends to shallower and shallower from the edgeof basin to its central, ranging from0.23m to9.47m; unconfined groundwater has decreased0.27~0.45m per year in the oasis agricultural zone of Chahaeran; confined groundwater andunconfined groundwater has decreased0.2~0.4m and0.2m respectively each year in theindustrial zone of Jilantai, and artesian well disappears. And in the desert hinterland,unconfined groundwater has decreased0.2~0.4m per year. More and more groundwatersupplied for industrial and agriculture should be counted as the main reason for groundwaterlevel being lower and lower in the industrial zone of Jilantai and oasis agricultural zone ofChahaer, which results in the hypersaline groundwater of salt lake flowing to oasisagricultural zone.Thirdly, the hydrochemical types of groundwater in Jilantai Desertification Basin tend tobe zonation, including recharge area, runoff area and discharge area along with the water flowdirection, and the quality of groundwater from recharge area to discharge area tends to beworse and worse. Salinity of unconfined groundwater and the percentage of fluorine ion tendto be greater and greater. The content of fluorine ion of60.5%unconfined ground water hasexceeded the standards of drinking water, which has a significant impact upon the healthy oflocal residences. What’s worse, the content of fluorine ion in confined groundwater isapparently higher than those in unconfined groundwater.Fourthly, the hydrochemistry in Chahaertan oasis tends to be salinization and alkalizationand hydrochemical types tend to be more complex and worse, which can seen from severalphenomena: Ca2+、Mg2+is saturate; Relative contents of HCO3-are decreasing although somepart of them are increasing; contents of nitrate and alkalinity of groundwater are increasing.The contents of Na+、Mg2+and Cl-of intercrystalline in Jilantai Basin tends to decline.Fifthly, the contents of fluorine ion tends to be more and more from recharge area in thepiedmont alluvial plain to runoff area and to discharge area in the centre part of desertificationarea. There are also some safe-islands of low-fluorine area among those hyperfluorine areasdue to microtopography and hydrodynamic power at some places, such as the fluorine ion ofgroundwater distributing characterized with annular island-shape in the sub-central salt lakeof desertification basin and low-fluorine annular groundwater existing within hyperfluorinegroundwater zone; stripped low-fluorine groundwater distributing along paleoriverchannel.Sixthly, bedrock in mountains and Aeolian sandy are the main sources of fluorine of unconfined groundwater in Jilantai Desertification Basin, continental arid climate and closuregroundwater system in the desert basin are the fundamental requirements for hyperfluorineenvironment. With the combination of geomorphology, runoff of groundwater, burial depth ofunconfined groundwater and depth of capillary water, human activities have an impact uponthe accumulation, migration and behavior characteristics of the fluorine. The contents offluorine in groundwater are positively correlated with the ratio of (K++Na+)/(Ca2++Mg2+) andsalinity, but no relationship with PH value. Under the same circumstance of salinity, thehardness tends to be higher, contents of Ca2+tend to be more, while contents of F-tends to beless.Seventhly, We used the theory of geological disaster risk evaluation, establishedthe evaluation model of groundwater’s fluoride environment quality partitions: Fi=αWi+βSi,we selected six risk assessment factors, including rainfall, topography, groundwater depth,aquifer’s lithology, the ratio of (K++Na+)/(Ca2++Mg2+) and evaporation; we also selectedthree vulnerability assessment factors, including population density, the percentage of thepopulation under the age of16, the population aged over56. The research of groundwaterfluoride environment quality partitions was carried on the platform of ARCGIS9.3[TM]software, with using information quantity method and AHP method. After that, Weconduct water quality health risk assessment of fluoride, non carcinogenic risk index as areference valuefor the pollution factor. High risk area is located in thecenter of the basin andBayan the North Piedmont, its area is3587.23km2, the area accounted for30.7%of studyarea, fluoride content in groundwater exceeded standard seriously.Eighthly, on the basis of Crystallization Kinetics Theory and Molecule Diffusion Theory,the mathematic model for microcosmic migration of fluorine ion was established in our study.Significant technical parameters were included, such as speed of crystal speed, velocity offluorine ion diffusion, repulsive interaction during the frozen dropping fluorine. The contentsof fluorine ion in the ice were determined by the density of mother liquid, frozen temperature,ratio of frozen and process of frozen. The natural frozen environment was represented byartificial refrigeration system; manual hyperfluorine water and hypersalinity were chosen asthe main water sample. Several frozen dropping fluorine tests were conducted. We summarizethe following rule: the effects of reducing fluoride among different freezing temperature, timeand concentration of different solutions for a variety of frozen conditions.Ninthly, six samples collected from unconfined groundwater containing hyperfluorineand hypersalinity was adopted in the confirmatory tests for frozen dropping fluorine, and tests show that: frozen dropping fluorine technique is quite beneficial to dropping fluorine anddesalination, the complexities and hypersalinity of nature groundwater might hinder the ratioof dropping fluorine. The hyperfluorine and hypersaline groundwater can not satisfy thecriteria of drinking water after just one frozen test and one test of dropping fluorine anddesalt.Tenthly, according to ratio of dropping fluorine and desalt, frozen temperature, density offluorine, taking the advantage of nature chilly climate in northwest hinterland of China, theoutdoor device at low temperature for automatically dropping fluorine and the general indoordevice for automatically dropping fluorine were designed to render hyperfluorine water dropfluorine and desalt, finally meeting the requirements of standard drinking water. |
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