Hydrochemical characteristics and formation mechanism of groundwater in Hohhot basin

On the basis o f hydr ogeo lo gical inv est igat ion and sample collectio n, w e used descriptive statistics, ionic ratio s, Piper trilinear diag ram, Gibbs diag ram, and Scho eller fig ur es to sy stematica lly st udy the g ro undwater in H ohhot basin. T he r esults show ed: ( 1) T he chemical com po nents of gr oundwat er ar e obviously co nt ro lled by the topog raphic and geomor phic facto rs and gr oundwat er occurr ence conditions. T he unco nfined and co nfined w ater in alluv ial2pr oluv ial pla in ar e mainly affected by weathe2 ring2dissolut ion of car bo nate and sulphate, and they ar e mainly the H CO32Ca # Mg type. In the center of alluv ial2lacustrine plain, evapo ratio n and ion2ex change reactio ns become the main co ntr ol pro cesses fo r hy dr ochemical components. ( 2) Fr om the edg es to the center o f alluvial2lacustrine plain, t he hydrochemical ty pes ev olv e r apidly. The catio ns evolve from the Ca# Mg # Na type to the Mg # Na and Na# M g ty pes, and end up w ith Na+ as the only dominant type. The anions evo lve fr om the H CO3 # Cl type, Cl # HCO3 type, Cl# SO4 type, to Cl ty pe in the end. ( 3) Near the surface water sy stem and irrig ation areas, the mix ing effect has obvio usly chang ed t he chemical compo sitio n of g ro undwater. In addition, t he influence o f human act ivit ies cannot be igno red. Aro und densely po pulated areas and major agricultural r eg io ns, ther e is hig h2 nit rog en gr oundw ater, which even caused the fo rmation of Cl# NO3 type gr oundw ater.

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