Evolution Characteristics And Mechanism Of Groundwater Total Hardness And Salinity In The Funnel Area Of The Hufu Plain

The area of shallow groundwater funnel in the Hufu Plain is the most serious overextraction area of shallow groundwater in North China.The mechanism of the abnormal change of hydrodynamic field in the funnel area on the increase of total hardness and salinity of groundwater has multi-source domain and multi-dimensional complexity.To solve this problem,this paper applies the hydrogeochemical theory,the evolutionary system theory of"driving force-state-response"and the analysis of time series variation and gradual-abrupt change,and obtains the following new understandings:1.Through diagnosis,identification and comparison of three periods and four zones,the variation characteristics of groundwater hydrodynamic field,total hardness and salinity in the funnel area are revealed.(1)In the past 50 years,great changes have taken place in the hydrodynamic field in the study area,which has driven the corresponding changes of the hydrogeochemical environment at the drainage horizon of the shallow water-bearing rock group in the funnel area.(2)The increase of total hardness and salinity of groundwater in the funnel area showed the characteristics of response and trend with the change of groundwater level decrease.In the early stage of funnel formation,the annual average groundwater level decrease and the increase of total hardness and its salinity are the largest,while in the middle stage,the decrease of the groundwater level and the increase of total hardness and its salinity are the smallest.2.By comparing with the non-funnel area,the variation characteristics of total hardness and salinity of groundwater in the funnel area are analyzed.(1)The response range of the groundwater salinity in the funnel area is significantly larger than that in the non-funnel area.For each 1.0 m increase in the drawdown of groundwater level,the increase range of groundwater salinity is 19.46?34.91 mg/(L.m)in the initial stage of funnel formation,and 8.33?20.83 mg/(L.m)in the middle stage and 7.05?21.15 mg/(L.m)at the end.(2)The total hardness and salinity of the groundwater in the funnel area are more sensitive to the increase of buried depth of groundwater level,but less sensitive to the rise of groundwater level.3.The multi-source and multi-dimensional factors influencing the increase of groundwater total hardness and salinity in the funnel area are identified.(1)The main driving factors of the increase of the groundwater total hardness and salinity in the funnel area are the groundwater dynamic field of the great drop of groundwater level and the formation of confluence,and the precipitation withering in successive years has a promoting effect.The two influencing areas are the main source areas of the groundwater total hardness and salinity increasing in the funnel area.(2)In different periods of the funnel formation,the composition and sequence of main influencing factors are variable.In the early stage,surface exogenous factors and climate change have significant effects,while in the late stage,groundwater system endogenous factors and lateral input from the upstream influence areas have significant effects.4.The formation mode and evolution mechanism of groundwater total hardness and salinity increasing in the funnel area are explicated.(1)The groundwater total hardness and its salinity increasing in the funnel area experienced,"single domain source two-dimensional effect"in the initial period of the funnel formation,"three domain source side increasing and external declining multi-dimensional effect"in the middle period of the funnel formation,and"three domain source side strong and external weak multi-dimensional effect"in the late period of the funnel formation.(2)The abnormal change of the groundwater dynamic field in the funnel area stimulates the enhancement of"strong leaching and dissolution"water-rock interaction in the drained aquifer and the groundwater level fluctuation zone.At the same time,the influence of lateral runoff and chemical component increment on chemical field variation of groundwater in the funnel area is enhanced by the strong suction and pumping of groundwater in the two upstream affected areas.(3)In the past 50 years,the total hardness and salinity of the groundwater in the funnel area have been increasing,and the order of contribution rate of main chemical components is Mg²⁺,Na⁺,Ca²⁺,SO₄^2-,Cl^-and HCO₃^-.In view of the fact that the groundwater in the funnel area is still in qualitative change,it is suggested that we should pay attention to the comprehensive control of groundwater over exploitation in the funnel area and strengthen the upstream mineral development and ecological restoration.