The Puding Village Underground River Basin Groundwater Vulnerability Assessment And Changes In Land Use Spatial Relations,

Groundwater vulnerability and its contamination potential analysis and mappingis a hotspot and frontiers of international hydrogeology study. It also is a prerequisiteto the work of preventing groundwater contamination problem. Groundwatervulnerability assessment mainly can be applied to groundwater protection,management and landuse plan.In this paper, the author firstly summarizes the concept, meanings, developmentand perspectives of groundwater vulnerability study, fully analyses the physicalgeography, karst geology and hydrogeology condition of the study area---Houzaibasin, Puding County, Guizhou province---a typical subterranean stream catchment insouthwest China karst. Furthermore the author establishes an assessment indexsystem and REKST model for groundwater vulnerability about the study area, andassesses the basin's groundwater vulnerability fully using the GIStechnology(ArcView3.2). Finally the author explains the relationship betweenregional groundwater vulnerability and landuse change based on a serialhydrochemical data from 1980 to 2002, and put forwards some landuse managementsuggestions on the basis of groundwater vulnerability assessment.Houzai subterranean stream basin is located in the southern part of PudingCounty, 103km away from Guiyang City, the capital of Guizhou Province, with anarea of 81km². It was one of the most important study areas of karst in southwestChina, thus a large amount of data and achievements on karst water resources andtheir exploitation has been accuinulated since 1970s.The stratum distributed widely in the basin is Guanling Formation (T₂g) ofMiddle Series of Triassic System. The main lithology is limestone, dolomite,marlaceous limestone and shale mixed with marlaceous dolomite. Folds are gentlewith lower dip angle from 7°to 25°. Subterranean stream mainly developed inlimestone of second section of Guanling Formation(T₂g²).Firstly, the key point in groundwater vulnerability assessment is to establish asuit of index system which is objective, systematic, and easily operational. Based on the fully discussion of various factors used and cited repeatedly by researchers inassessment of groundwater vulnerability, the author sorted and selected Rock,karstification, Epikarst, Soil and Topography as assessment index integrated withgeo-hydrology characteristics of study area, and established the REKST model. In themodel, karstification is used to depict infiltration condition, with consideration ofpoint infiltration, such as karst depressions, sink holes, swallow holes, and farmlandirrigation affect. Epikarst is used to depict vadose zone. Furthermore landuse changewas taken into account in the Context of Soil. So the assessment procedure includedaquifer vulnerability components not only intrinsic, but also special, thus succeededin the transition from single intrinsic vulnerability assessment to integratedassessment.Groundwater vulnerability involved in this paper mainly is based on the intrinsic,namely focused on internal factors of karst hydrogeology, partially contaminationsources and anthropogenic activities. Integrated with local condition of Houzai basinthe index system is listed below (Table 1):The parameter's weight in REKST model was assigned according to the basin'sactuality, groundwater vulnerability index is formulated below(figure meanscorresponding weight of each parameter): REKST=2×R+5×K+3×E+4×S+1×T In assessment process, the author takes full advantage of GIS, includingparameter layers' digitization, map layers' overlay, weight and rating assignment ofeach parameter, vulnerability index's calculation, etc.. Integration betweenvulnerability assessment and GIS technology is quite favorable for spatial dataprocessing and management, including data collection and edit, spatial databaseestablishment, map and spatial analysis. It can offer visual, available informations todecision-maker and administrators.The results of groundwater vulnerability ranks(Table 2) (totally five classes aredivided) show that vulnerability degree in most of the basin is lower. The area ofquite high and high vulnerability is only about 2.69km², 2.5% of total basin area. Itdistributes mainly in watershed area in which Fengcong depression located, and in thevicinities of sink holes(rank 5), and around the middle reaches of basin(near Laohetanto Liugu). Generally, along the subterranean stream, the vulnerability descends frommidstream(near Liugu-Laohetan), upstream(near Muzhudong-Dayouzai) todownstream(Houzai) with rank 3-4, 2-3, 1-2 respectively. The result also is proved bythe hydrochemical data, namely the higher vulnerability is, the higher groundwaterion concentration is.Moreover, the large-area class 2 farmland (near Daxing, Liugu and Aliangzai)have quite high vulnerability may resulted from their location (midstream), thin soillayer, flood irrigation, affects of upstream contamination and agriculture activities. The relationship between vulnerability rank and landuse shows that lowervulnerability area mainly distributes in the north part of basin near Qingshan reservoirand Chengjialaofen, primary dry farmland in the basin underlain by lowerkarstification dolomite. This phenomenon indicated that vulnerability in dolomitearea is lower than that in limestone area within the same basin. Furthermore,vulnerability near the transition zone between Fengcong depression and Fenglinvalley also is lower. This area mainly located in Fengcong side with mid dissolutionrate and massive limestone(T₂g^2-3), it indicated that the lithology is a very importantfactor impacted on vulnerability.Mostly class 1 farmland and watershed area with high dissolution rate limestoneand marl(T₂g^2-1) have medium vulnerability. Class 1 farmland has highercontamination resistivity because of thick soil layer, high organic content whereasflood irrigation always happens in irrigation season every year.Secondly, the author discusses and analyzes the relationship betweengroundwater vulnerability and landuse change based on a series of hydrochemicaldata(1980-2002), and finds that whether strengthen of agriculture(industry) activities,change of landuse type, or change of irrigation system will cause the spatio-temporalchange of groundwater quality, in which someare unfavorable, such as urbanization,contamination's direct discharge, overuse of pesticides and fertilizers; some arefavorable, such as joint irrigation control of surface and subterranean reservoir,vegetation planting(from farmland to forest). So groundwater vulnerability should beconsidered in process of landuse program. Water and soil resources should be treatedeco-friendly and use effectively and rationally from systematic view and groundwaterprotection standpoint, by using science and technology at most to developeco-agriculture, improve irrigation system, plant trees and control contaminationdischarge.For example, some water resources exploitation projects integrated witheconomy construction have been put in practice since earlier 1990s. Muzhudong area,located in upstream Fengcong area, begins to plant poplar for increasing income andwater supply at that time, sulfate content of subterranean stream decreases gradually after the afforestation. A few years later karstification condition improved, thuscalcium content increased and entironment changed evidently.In addition, the difference of average degree of mineralization between irrigationperiod(from April to May) and later rainy season(from June to September) begin todecrease remarkably at the end of 1980s, thereafter decrease gradually year after year.It indicated that with the change of landuse(from farmland to forest) and reduction ofagriculture activity has remarkable impact on seasonal distribution of degree ofmineralization.Groundwater pollution caused by landuse change is not only a resource problembut also an environmental problem. Moreover, they are closely associated and form alarge system with other resources. So it is necessary to strengthen the understand ofcharacteristics of land use effectively and rationally in karst area, and establish benigncycle of resource system as experience happened in Muzhudong area in earlier 1990s,thus improve harmonious development between human activities and resourceenvironment.Now protection and rational use of water resources has risen to the sustainabledevelopment level. It is predictable that in the twenty first century people willstraggle for water resources protection, and pay great attention on water qualityproblem, carry out more and more investigations on groundwater vulnerabilityassessment and mapping focused on groundwater protecting techonology(especiallyharness technology).Groundwater vulnerability assessment is a very important means for aquiferprotection. The study area in the paper is a typical area in southwest China karst, andthe study is aimed at non-point contamination problem(caused by agricultureactivities) that is common but hard to control and treat. So the results in forms of mapcan help understand the relationship between landuse and groundwater contamination,identify groundwater high-risk section to pollutant, thus help decision-maker andadministrators establish corresponding groundwater protection strategy and policy.Meanwhile, with geological map and other data, aquifer spatial data(map) of thestudy can give key element for decision making, such as water resource deficient,environment protection. From 2000 new round geological investigation has been put into implement, its main objective is to offer basic fact and explanation to planner viamapping practical theme map, and provide scientific support for landuse andenvironmental plan. Accordingly, the results of this study can provide service forgeological investigation in China karst area.