| In China,the Jinghe River Basin is one of the birthplaces of agricultural and animal husbandry civilization,as well as an important energy and chemical base.In recent decades,obvious climate changes and ecological construction including returning farmland to forest/grass,construction of gas and oil field energy bases,industrial and domestic sewage discharge,excessive use of agricultural fertilizers,and new town construction,and so on,have caused significant changes in the quantity and quality of water resources in the Jinghe River Basin.Under the influence of the changing environment,how to change the quantity and quality of water resources,and how to delineate groundwater pollution sensitive zones for possible groundwater pollution problems are issues that need to be studied in depth.For this reason,this study started with the characteristics of the changing environment in the Jinghe River Basin,and analysed the evolution characteristics of runoff and base flow in the Jinghe River Basin.Based on the base flow and water balance principle,the amount of groundwater resources in the Jinghe River Basin was calculated,spatio-temporal evolution patterns of the groundwater depth,groundwater hydrochemistry and water quality were analyzed.Finally,based on the results of groundwater quality evaluation,the spatial distribution of inherent vulnerabilities and special vulnerabilities of groundwater in the Jinghe River Basin was discussed.The following main conclusions were obtained:(1)Characteristics of runoff evolution and driving force change in Jinghe River BasinUsing Mann-Kendall method and other methods to analyze the precipitation and average temperature in the Jinghe River Basin from 1960 to 2019,the results showed that the annual precipitation and average temperature increase rates were 10.4 mm/10a and 0.3?/10a,respectively.The annual average temperature showed an obvious increasing trend,and the mutation year was 1995.After 2000,the land use type change was more obvious,which showed that the construction land and grassland increased significantly,and the cultivated land area decreased obviously.On the whole,the water consumption,terrace area and silt dam construction were increasing with time.The results of linear trend analysis showed that the runoff of Jinghe River Basin decrease at the rate of 6.4 m3·s-1/10a.Mann-Kendall mutation test and analysis of quantitative index of variation determined that the runoff mutation year of the Jinghe River Basin was 1999.(2)Quantitative assessment of impact of changing environment on Runoff in Jinghe River BasinThe fitting empirical formula and mathematical statistics method were used to analyze the contribution of the main driving forces to the change of runoff.The results showed that the contributions of multi-year average precipitation,water consumption,terrace measures,dams,and land use types to river runoff changes were 0.65×108 m3,1.8×108 m3,0.8×108 m3,0.2×108 m3,and 0.03×108 m3,respectively.On the whole,the driving force for the decrease in runoff was the direct use of surface water by humans,followed by terrace measures.The calculation results of the Wet Spa model with the addition of the water extraction module all indicated the effect of water conservation measures in flood storage and drought compensation to some extent.(3)Evolution of groundwater in the Jinghe River Basin under the influence of changing environmentThe base flow calculated by Wetspa shows a decreasing trend with time.The annual average groundwater resources in the Jinghe River Basin is 9.2×108 m3.Precipitation recharge and base flow discharge are the main recharge and discharge methods of groundwater.There are differences in the main anions and cations of the Cretaceous groundwater in the three periods.In 1979 and 2004,the groundwater cations and anions were dominated by Na+and SO42-,respectively.Compared with 1979,the percentage of milliequivalents of main anions and cations in groundwater has declined.In 2015,the anion in groundwater was mainly HCO3-,and Mg2+was the main cation.The main hydrochemical types of Cretaceous groundwater samples have changed,and the conversion was from SO4 type water to HCO3 type water.The spatial distribution characteristics of groundwater chemistry are mainly affected by natural factors,but under the intervention of human activities,the spatial distribution of groundwater chemistry types presents more complex and changeable characteristics.On the whole,the concentration of NO3-,Fe,Mn,hexavalent chromium,and As ions in the groundwater gradually increased with time,and the content of TDS,TH,Cl-,SO42-,NO2-gradually decreased with time,while the F-ion concentration increased and then decreased.The triangular fuzzy number health risk assessment results show that both the carcinogenic risk of arsenic and the non-carcinogenic risk of nitrate in groundwater will have significant adverse effects on the health of sensitive people.In2015,the non carcinogenic risk of nitrate in groundwater was latent in the whole Jinghe River Basin,which was mainly caused by human pollution.(4)Groundwater vulnerability assessment of Jinghe River BasinBased on the meteorological and hydrogeological conditions of the Jinghe River Basin,an index system suitable for the evaluation of the gorndwater vulnerability was constructed.The coupling method of entropy weight and analytic hierarchy process was used to calculate the weight of each index.The vulnerability assessment results show that the depth of groundwater and net recharge are important factors affecting the spatial distribution of groundwater inherent vulnerability,and their contribution amounts to51.5%.High and high groundwater vulnerabilities are mainly distributed in river valleys and western karst areas,which are caused by the buried depth of groundwater and the medium in the seepage area;the certainty coefficient(R2)between the concentration of nitrate in groundwater and the special vulnerability of groundwater reached 0.41(linear regression)and 0.5(exponential regression),indicating that the improved DRATI-LE model is reasonable and feasible,and also illustrate the complex nonlinear relationship between groundwater vulnerability and evaluation indexs.The calculation results can provide a scientific basis for groundwater resources protection. |
PDF Full Text Request