Study On The Formation Mechanism Of Natural Mineral Water In Jingyu National Nature Reserve

The thesis is supported by the key scientific and technological project of JilinProvince which is “Analysis of the formation mechanism of Changbai Mountainnatural mineral water”(No.20100452). Based on the basic data collected, includinggeological, hydrogeological, meteorological, springs discharge and remote sensing, asystematic study was conducted on the formation mechanism of natural mineralwater in Jingyu national nature reserve from three aspects, which are regionalenvironment, groundwater circulation and water-rock interaction mechanism, with thethe method of combining qualitative and quantitative analysis and the means ofmutual authentication between field survey and laboratory analysis.(1) Analysis of regional environmentGIS and RS were applied to analyze the topography and land cover types of thestudy area. Basalt plateau in the study area has a flat terrain with average slope of3.02°and the major types of land are forest and swamp, with total area of190.9km2,accounting for91.1%of the study area. Swamps cover an area of38.5km2,accounting for18.4%of the study area, which are mainly located in the northeasternand southwestern of the study area. Projection pursuit cluster model was applied toassess the eco-environmental quality with12indicators. The result shows that theeco-environment of Jingyu national nature reserve is grade1. Special terraced terrain,lush forests and a large area of swamp, are all favorable conditions which providegood water conservation and supply conditions for mineral water and excellent andstable eco-environment is reliable ecological barrier which guarantees excellent waterquality. Basalt of the study area is classified as olivine basalt, mainly composed ofolivine, plagioclase and pyroxene, with50.20%average content of SiO2. Specialgeochemical background is the foundation of the chemical compositions of mineralwater. Basalt can be divided into many layers from up to down. Stomatal layers,Scoria layers, fissures and tectonic fractures constitute a complex storage anddrainage system for groundwater, forming a unique lava pore-fissures groundwatersystem. Permeability coefficient moves between0.23and0.50m/d, obtained from thepumping test for the test wells.Chemical types in the study area are mostly of HCO3-Ca-Mg or HCO3-Ca-Mgand keep stable, controlled by special geochemical and hydrogeological conditions.The concentration of silicic acid has s significant spatial variance structure in thestudy area. With increasing depth, concentration of silicic acid increases significantly,and the average concentration of silicic acid of springs in the central is slightly higherthan in the northeast, which indicates that groundwater runoff occurs mainly inshallow and central, while deep groundwater moves slowly.(2) Groundwater circulationIsotopic analysis of water samples from springs and test wells were carried out,including stable isotope D and18O and radioactive isotope3H. Most of the samplesscatter fall below the LMWL (local meteoric water line) of Changbai mountains andalong the local evaporation line, which shows that groundwater in the study areaoriginates from precipitation, even though little or a little evaporation occurs.Evaporation increases gradually from the southwest to the northeast, meanwhilevalues of18Oand Dat different depths have large difference, which reflectsdifferent recharge conditions. According to the calculation result of3H, the isotopicages of Kanglian and Beishang are the youngest and of ones of the central includingBaijiang are the oldest with3H isotopic age older than40a, while in the northeastisotopic ages are the lowest, younger than35a. Isotopic ages show a"Young-old-Young" U-shaped spatial distribution, which reflects the relativeindependence of groundwater system of each spring catchment.Based on77volcanoes in and adjacent to the study area and four construct pointsfound during the field investigation,10faults of under overburden were inferred using the methods of Fuzzy c-lines and L_MSCMO. Basalt formed by nulti-stage magmaticeruption covers the ancient basin forming a basin-shaped storage structure. Affectedby neotectonic movement, many tectonic fissures and rock broken rocks occurredalong old fractures, based on which some water-conducted paths were formed. It iswhy springs outcrop with shapes of clusters or lines. In this paper, acatchment-divided method considering synchronously the impacts of faults andsurface catchment basin was presented which was applied to the Shenglong-Jiulongspring-clusters and Julong-Feilong spring-clusters. The results show that, the areas ofcatchments of the two spring-clusters are26.9km2and45.5km2respectively, andcoefficients of rainfall infiltration rate calculated without considering other dischargeitems are0.317and0.332respectively. The dynamic changes of springs are mainlyaffected by precipitation and groundwater runoff. The daily flow is related with thecumulative rainfall. The fluctuation of average monthly flow has a lag time comparedto the rain, which is depended on the recharge environment.(3) The mechanism of water-rock interactionIn order to study the interactions between groundwater and water-bearing mediaincluding basalt, volcanic slag and soil interactions, static immersion and dynamicleaching experiments were designed. The interactions between groundwater and thethree media are mainly characteristic of the hydrolysis of the silicate and aluminumsilicate minerals.Concentrations of silicic acid increased with time in the early and graduallystabilized. The concentration of silicic acid in soil soaking is the highest, the second inthe scoria soaking and the lowest in the basalt soaking. Overall, pH values were beingon the rise throughout the experiment in the three soakuings, and respectivelystabilized in the final stage. Concentrations of ions except Cl-increased quickly in theearly and stabilized in the final stage. Concentration of Cl-in soil soaking is positivelycorrelated with pH values, because-NH2of soil has adsorption behavior to Cl-. Theamount of dissolved silicic acid in scoria soaking is higher, but the values of otheritems are the lowest of the three soakings, which is related to the precipitation-leaching environment. The unique soil environment of the study area hasan important influence on the formation of mineral solute components.The value ofpH of soil layer in the study area is about5.0~5.5. It not only is a important source ofsolute components and CO2, but also provides an environment with low pH, whichpromotes interaction between groundwater and basalt. Leaching experiments showedthat hydrolysises of vasalt and scoria have faster rate in flowing water than in stillwater. Water’s motion not only accelerates the convection and diffusion ofcomponents in solution, but also erodes the middle layer consist of secondaryminerals.Reverse and forward hydro-geochemical models were established based onPHREEQC and TOUGHREACT respectively. The main chemical reactions ofwater-rock interaction are hydrolysis of feldspar, pyroxene and forsterite along thegroundwater flow path, while feldspar is the dominate, from which silicic acid inaqueous solution derives. Ca-montmorillonite is the key aluminum silicate precipitate,while na-montmorillonite and kaolinite precipitate a little. Cation exchange occursstrongly which is characterized with that Ca2+of groundwater substitutes Na+ofbasalt.A conclusion can be easily drawn from the results of TOUGHREACT model,that fractures change the form of the groundwater flow field and acceleratedgroundwater circulation, which will correspondingly change water-rock interactionprocesses of groundwater systems and the concentrations and spatial distributions ofdissolved components eventually.