Geochemical Characteristics and Influencing Factors of Groundwater Fe in Seawater Intrusion Area

Abstract

To reveal the influencing process and mechanism of seawater intrusion on groundwater Fe in coastal zones, the local groundwater in Buzhuang Town, together with those in the neighboring area where no seawater intruded, was sampled and comparatively analyzed, and the static simulation experiments were also performed in laboratory. The local groundwater has Fe levels of 6.09–196.96 μg/L, with an average of 73.38 μg/L, but groundwater Fe levels from the neighboring area are 1.3–17.7 times of those in local groundwater. Such facts indicate the groundwater Fe levels decreased due to seawater intrusion. The groundwater Fe levels are significantly negatively correlated with pH, significantly positively correlated with Ca2+, Mg2+, and positively correlated with SO42−. The simulation experiments indicate leached Fe increases with a greater mixture of seawater, increasing concentrations of NaCl and CaCl2, but decreases with increasing NaHCO3 concentrations. Fe(OH)2 and Fe(OH)3 minerals are super-saturated because of the high pH and high OH− concentration resulting from seawater intrusion. By this way, the dissolving ability of groundwater Fe is restricted. Therefore, pH is the key factor determining groundwater Fe levels in coastal zones. Another, the decreasing of Ca2+, Mg2+ in groundwater decreases Fe levels because of the co-precipitation and deactivation of groundwater Fe. Salt effect and NaHCO3 contribute less to groundwater Fe levels because of the restriction of maximum Fe solubility by high OH− and super-saturation of Fe-bearing minerals. The influencing model of groundwater Fe levels under the effect of seawater intrusion is forwarded.