Reseacrh On The Impacts Of Land Consolidation On Groundwater Environment And Risk Assessment For Irrigation Districts In Western Jilin Province

Irrigation districts in western Jilin Province are typical areas of the ecotone withfrangible eco-environment. They belong to arid and semi-arid continental monsoonclimate with less precipitation, high evaporation. Because impacts of environmentalchange and human factors, eco-environment is deteriorating, and soil salinization problemis aggravating in western Jilin Province. Their consequences are often potential, pervasiveand persistent.Jilin Province is an important commercial grain production base in China. To solvethe problems of land degradation, and establish the ecological agriculture irrigationdistricts in western Jilin Province, we need to carry on land consolidation for the purposesof eco-environment improvement and grain production growth. The impacts of landconsolidation on groundwater environment are both beneficial and adverse. In this paper,on the basis of hydrogeological data collected in the study areas, we analyze effects ofland consolidation on groundwater environment of the low plain areas, including Wujiaziirrigation district, Daan irrigation district and Songyuan irrigation district in western JilinProvince. It is an important significance to achieve the sustainable development ofirrigation districts. The researches obtained in this paper are as follows:1. We collect the existing informations in order to analyze the regional geology andhydrogeology of the study areas. The water quality types in the study areas most are thecalcium bicarbonate type water and heavy calcium carbonate, sodium-type water. Thewater quality conditions of selected37groundwater samplings are analyzed by usingcomprehensive evaluation score method. The analysis show that the phreatic water qualitytypes in the three irrigation districts are all class IV or V. They are not suitable for drinking.The irrigation water quality conditions are analyzed in section of the NenRiver white sandbeach, the NenRiver water port of Daan irrigation district and the Songhua River. Theresults show that the irrigation water quality can basically meet the requirements ofirrigation water. 2. The impacts of land consolidation on groundwater quantity and groundwater levelfor irrigation districts are analyzed by using the principle of water balance and thenumerical simulation of groundwater flow, respectively. The results show that after theland consolidation, the groundwater recharge of Wujiazi irrigation district, Daan irrigationdistrict and Songyuan irrigation will be respectively increasing by28%,36%and29%ataverage annual conditions, and the groundwater level will be respectively rising by0.8m,0.6m and0.4m in10years. The groundwater level will remain dynamic equilibrium whenthe groundwater level is rising to drains backplane.3. The impacts of land consolidation on groundwater quality of irrigation districts areanalyzed. Through the law of conservation of mass, the mineralization degree ofgroundwater will decrease. we adopt in-house experiment to analyze theadsorption-desorption properties of nitrate-nitrogen in soils. The result is thatnitrate-nitrogen in soils is mainly desorption. The impacts of nitrogen fertilizers on humanhealth are that the risk index values are less than1, through the health risk assessmentmodel (HRA) proposed by U.S. EPA. The result is that using fertilizer in irrigationdistricts has little impact on human health risk. Because of pesticide’s short half-life, it haslittle effect on groundwater environment.4. The return water qualities of irrigation are analyzed in the moon bubble easternirrigation district of Daan city and Qianguo irrigation district, respectively. In return areas,the quality of return water, water evaporation and salt accumulation, which are affected bythe pesticides and fertilizers for Wujiazi irrigation district, Daan irrigation district andSongyuan irrigation, are analyzed by using the analogy method. The results show thatusing pesticides and fertilizer will have little and certain impacts on the return areasrespectively, return water will basically be evaporated and bicarbonate accumulations inreturn areas will be5.66×104t,10.23×104t and26.73×104t in10years.5. The drought is a natural phenomenon of water imbalances. In this paper, thecharacteristics and trends of drought for the irrigation districts are analyzed. Based onexisting informations of irrigation districts, the drought characteristics of irrigationdistricts are analyzed by P-III frequency curve and precipitation anomaly percentage. Theresults show that the annual precipitation changes of irrigation districts are less stable, and drought years of three irrigation districts are all more than20%. Gray system theory isused to predict droughts of irrigation districts.6. The groundwater withdrawals for irrigation districts can be calculated by usingmineable coefficient method. On condtion that the maximum groundwater withdrawals ofWujiazi irrigation district, Daan irrigation district and Songyuan irrigation district are2624.85×104m~3/a,7000.69×104m~3/a,27163.90×104m~3/a respectively, the exploitations ofgroundwater usually do not cause droughts of lower reaches.7. The irrigation district is a complex agricultural system. A multi-objectiveoptimization model of agricultural planting structure is built. In this model, thewater-saving benefits, economic benefits and ecological benefits of irrigation district areconsidered. Minimun consumption of water, the maximum production of crop andmaximum of eco-efficiency, which are optimal targets. The area and irrigation water areconstraints. The model of the irrigation district for Wujiazi is calculated by usingefficiency coefficient method. The results show that crop planting structure is optimizedon condtion that rice and corn are only planted in Wujiazi irrigation district.8. According to the representative, comprehensive and systemic principles ofindicators selected, four evaluating indicators and seventeen evaluating factors includingnatural condition, water environment, soil environment and irrigation districtsenvironment are selected. The seventeen evaluating factors include groundwater naturalprotection ability, drought index, recharge modulus of groundwater, exploitable modulusof groundwater, buried depth of groundwater table, total mineralization degree ofgroundwater, the degree of groundwater development and utilization, irrigation watersalinity, irrigation water alkalinity, irrigation water mineralized degree, soil salinity, soilalkalization, soil organic substances content, canal system layout, fertilizer applicationintensity, pesticide application intensity and environmental protection awareness. Inaccordance with four-level building layers, including the target layer, criteria layer I,criteria layer II and basic indicators layer, the index system of groundwater environmentrisk for irrigation districts is constituted. In addition, according to National Institute ofStandards, the relevant standards of Industry and local regulations, and other standards ofsimilar areas, each evaluation factor is analyzed and divided to five risk levels which areno-risk, slight risk, medium risk, significant risk and absolutely risk. The index system is comprehensive and easy to be quantified. It can provide a reference for groundwater riskassessment of other irrigation districts.9. Using fuzzy comprehensive evaluation method, catastrophe theory and the powerfunction exponential model, the groundwater environment risks for three irrigationdistricts are comprehensive analyzed. The establishment of index system for groundwaterenvironment risk in the irrigation district is whether reasonable by using the sensitivityanalysis method. The analysis results show that each index sensitivity value is no morethan5, the evaluation results are not sensitive to the error. The establishment of indexsystem for groundwater environment risk in the irrigation district is reasonably practicable.Before land consolidation, the groundwater environments of three irrigations have somerisks and all belong to slight risk status. The obtained results are consistent with actualcondition. After land consolidation, groundwater environments of the three irrigationshave no risk. The results show that groundwater environment for irrigation districts inwestern Jilin will be better because of the land consolidation.