Ground water copper levels in the seawater intrusion area and the possible physical and chemical dynamics

Abstract

Seawater intrusion, a common geological process along the coastal zones, changes the groundwater properties, which are potentially associated with the groundwater copper (Cu) levels. However, there are no studies on the details of groundwater Cu levels affected by seawater intrusion. The groundwater in the seawater intrusion area of Buzhuang Town was sampled to detect the effect of seawater intrusion on groundwater Cu levels. The Cu levels in the local groundwater range between 0.92 and 4.99 μg L⁻¹, which averages about 5 times than those in the non-intrusion area. The Cu deviations (ΔCu) are positive, and increase with more intrusion of seawater. Simulation experiments also confirm that more Cu leaches from sediments when more seawater or brine water is mixed in. The groundwater Cu levels are positively correlated with TDS, Cl⁻, Br⁻, SO₄²⁻, HCO₃⁻, Na⁺, K⁺ and Mg²⁺. The Cu-bearing minerals in the local groundwater are under-saturated. The CEC of the sediment for the simulated experiments decreases with more mixture of seawater or brine water. CuCO⁰₃, Cu(OH)⁰₂, CuHCO₃⁺, Cu(CO₃)₂²⁻, CuCl₂⁻, Cu²⁺ species in the local groundwater are obviously higher than those in the non-intrusion area, and the levels of CuCl₂⁻, Cu⁺, CuCO₃, Cu²⁺, CuSO₄, CuOH⁺, CuCl⁺, Cu₂(OH)₂²⁺ are positively correlated with the degree of seawater intrusion, indicating the important role of Cl⁻, HCO₃⁻, OH⁻ complexation on groundwater Cu levels. Thus, ion competition and complexation are the important dynamics of groundwater Cu enrichment along the coastal zones. A new enrichment model of groundwater Cu in the seawater intrusion area is presented. Seawater intrusion should be taken into consideration when the enrichment mechanisms of groundwater Cu are discussed.