Abstract:

Surface water-groundwater interaction, which not only affects groundwater chemical evolution, but also controls spatial distribution of groundwater components, is one of the important issues in the groundwater field. Fifty-eight groundwater samples and thirty-two rainwater and surface water samples were taken from the Hetao basin, Inner Mongolia. Major components, trace elements and water isotopes were analyzed in those samples. Results showed that surface waters were affected by human activities and evaporation, which contained elevated concentrations of Na⁺, Ca²⁺, SO^2-₄, and NO^-₃. Shallow groundwater had the similar major components and isotopic characteristics with surface water, which indicated that shallow groundwater was affected by surface water. During the infiltration of surface water into the shallow aquifers, incongruent dissolution of silicate minerals, congruent dissolution of halite, barite precipitation, reduction of NO^-₃, Fe oxides and SO^2-₄possibly occurred. Reductive dissolution of Fe oxides was the major cause of high As concentration in shallow groundwater. Arsenic concentration was also affected by  SO^2-₄ reduction. Therefore, synthetical investigation of surface water and groundwater would help to reveal hydrogeochemical processes in aquifers.

Key words: water-rock interaction, contamination, redox, hydrogeochemical process, the Yellow River