Groundwater Hydrochemical Characteristics And Hydrogeochemical Processes Approximately Along Flow Paths In The North China Plain

The North China Plain （NCP） is one of the most water scarce areas in China, with about450m³water resources per capita. The shortage of water resources has seriously impactedeconomic development of NCP. In recent decades, the hydrochemistry characteristics and naturalgroundwater flow system, including recharge, runoff and discharge conditions, have beenchanged greatly due to the influence of dry climate, rainfall decrease, increased exploitation andhuman activities. They resulted in a series of resources and environmental problems, whichbecame the hot focus of the international hydrological study. It is important to study groundwaterevolution characteristics and hydrogeochemical processes in the North China Plain.This paper comprehensively utilizes hydrochemistry, isotope and inverse hydrogeochemicalmodeling, combining the hydrogeological conditions and groundwater evolution information ofthe NCP to study the chemical characteristics and hydro-geochemical processes. In addition, thispaper also focuses on analyzing the characteristics of fluoride and the causes of high fluoridewater. The results of this paper listed as below:1. As a whole, geochemistry of local groundwater has obvious zonation patterns from thestrongly runoff zone （Zone I）, through the slow runoff zone （Zone II）, and to the discharge zone（Zone III）. From Zone I, through Zone II, to Zone III, the hydrochemical types of groundwaterchange from HCO₃-Ca·Mg, HCO₃·SO₄-Ca·Mg types, through HCO₃·SO₄-Ca·Na,SO₄·Cl-Na·Ca, SO₄-Na types, to SO₄·Cl-Na, HCO₃·SO₄-Na, Cl-Na types.2. Results of hydrogen and oxygen isotope show that groundwaters in Zone I originatedfrom precipitation, and undergo evaporation before recharged. The poor of hydrogen and oxygenisotope in Zones II and III of deep aquifers is related to the environment conditions of formation.The deep groundwater was old, which has lower δD and δ¹⁸O values due to low temperatureduring the recharge of precipitation. So, the hydrogen and oxygen isotope from deepgroundwater may reflect the groundwater recharged from precipitation in glacial or interglacialperiods, when the the climate is cold.3. The main hydrogeochemical processes occurring in groundwater systems includehydrolysis process, evaporation, ion exchange and oxidation-reduction process, which decidedthe chemical characteristics of the North China Plain. The groundwaters from Zone I are affectedby dissolution-precipitation, ion exchange, and weak evaporation. The groundwaters from ZoneII are affected by dissolution-precipitation, ion exchange, and strong evaporation and sulfate reduction. The deep groundwaters from Zone III appeared weak reduction, which is the onlydifference from Zone II. Results of inverse modeling are consistent with these processes.4. The types of high fluoride water are complicated. Alkaline soda-type water is moreconducive to fluorine enrichment. However, Ca²⁺and Mg²⁺inhibit the release of fluoride in thewater. The genesis of high fluoride water relates to the environmental conditions of itsoccurrence and migration. Fluoride concentration in Zone I is low. The high fluoride shallowgroundwater in Zones II and III are mainly controlled by evaporation because of stagenant flowconditions and high groundwater levels. The high fluoride deep groundwater in Zones II and IIIare dominated by fluorite dissolution, calcite precipitation, fluoride desorption and cationexchange.