Study On Mechanism Of Groundwater Chemical Evolution And Technology Of Source Apportionment In Hutuo River Alluvial-Pluvial Fan Region

Recently,with the acceleration of the rapid urbanization and industrialization,the influence of human activities on groundwater environment has increased year by year,which resulted in the significant changes in the characteristics of groundwater and devalued its usage.As a result,it is urgent to study the evolution mechanism of the groundwater chemistry and analyze the contamination sources.In this research,the Shijiazhuang section of the Hutuo River alluvial-pluvial fan was selected as the study area.Through periodic water quality monitoring and laboratory test analysis,combined with hydrochemistry,multivariate statistical techniques,isotope geochemical theories and source analysis models,the chemical evolution mechanism and the identification technology of pollution source of groundwater in the area with intense human interference was studied.The main contents are as follows:（1）The hydrochemical characteristics and evolution of groundwater in Hutuo River alluvial pluvial fan were studied.The results showed that the groundwater was significantly affected by human activities,and the highest exceeding rate of inorganic indexes was TH and NO₃^-.As a toxicological index,NO₃^-was the most important threat in the local drinking water.With the enhancement of human activities,the groundwater hydrochemical types in the study area have shown a diversified development trend.The proportion of SO₄-type and Cl-type water has increased.In the middle part of the alluvial fan,the groundwater hydrochemical type was mainly HCO₃-Ca（Mg）-type（54%）,while it was transferred to HCO₃·SO₄-Ca type water in the Hutuo River valley and the top of the alluvial fan,accounting for 73%and 43%,respectively.In recent years,the evolution of groundwater environment in the study area was mainly influenced by human activities,followed by natural factors,the evolution pattern of which was in theⅣcategory of evolution mode.（2）The driving mechanism of groundwater quality deterioration in the rapid urbanization process was studied.The results showed that with the acceleration of urbanization and industrialization,the groundwater level in Shijiazhuang presented a stepwise continuous downward trend.Urbanization has seriously affected groundwater quality.NO₃^-and TH in groundwater were the most sensitive indicators affected by human activities in rapid urbanization areas.The groundwater quality was closely associated with the socio-economic development of the region.Except for p H and HCO₃^-,the other water quality parameters showed an extremely significant positive relationship with GDP,permanent population and population density.The level of urbanization also showed a significant positive correlation with Cl^-,Mg²⁺,NO₃^-,salinity and hardness.The main controlling factors on the deterioration of groundwater quality in rapidly urbanized areas are population growth,socio-economic development and the water-rock interaction caused by the strong exploitation of groundwater.The research results further indicated that with the rapid social and economic development,much more attention should be paid on the quality of groundwater.（3）The groundwater quality and the pollution source of the Hutuo River alluvial fan area was studied.The results demonstrated that the main pollution factors on the groundwater quality in the study area were NO₃^-,SO₄^2-and TH.The spatial variation of groundwater quality was mainly related to the groundwater depth,while the temporal variation of groundwater quality was mainly affected by rainwater dilution.The result of multivariate statistical model identified that domestic sewage was the main pollution source of groundwater in the study area in three seasons.The results of PMF model showed that in dry season the main pollution source of groundwater was domestic sewage,while in wet season and normal season were non-point source pollution and water rock interaction.Base on the comprehensive analysis of the two models results,it showed that with its own verification program,the accuracy,reliability and accuracy of the source analysis results in PMF model were higher than that in the absolute principal component analysis multiple linear regression model.PMF model is worth promoting and applying in the water environment traceability work.（4）The mechanism of tracing the nitrate pollution source in water environment by multiple isotopes was studied.The results indicated that the buried depth of groundwater level and land use types had a significant impact on the nitrate concentration in groundwater.Rainfall was the primary replenishment source for groundwater and surface water in this area.There was a close hydraulic relationship between surface water and groundwater.Based onδ¹⁵N-NO₃^-andδ¹⁸O-NO₃^-traceability technology,the nitrate pollution source in groundwater may come from the mixed pollution of domestic sewage,manure,soil nitrogen and ammonia fertilizer.The utilization ofδ³⁷Cl isotope tracing theory further improved the accuracy of source analysis results.Nitrification was the main migration and transformation mode of nitrogen in groundwater in Hutuo River alluvial fan.（5）The quantitative source analysis technology of isotope was combined with SIAR model.The results showed that in the Hutuo River alluvial fan,the main sources of groundwater nitrate pollution in different hydrogeological units were domestic sewage and manure.In the dry season,domestic sewage and manure accounted for a large proportion,ranging from 55.9%to 61.0%.While in the normal and wet season,due to the dilution of the rainfall,the proportion decreased to50.3-60.4%and 42.7-47.6%,respectively.Therefore,it was in the first place to control the indiscriminate discharge of domestic sewage to the control of groundwater nitrate pollution in the study area.