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

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.

The experimental study of fluorine-leaching ability of granite with different solutions: A new insight into the dynamic of groundwater fluorine levels along coastal zones.

Drinking-water fluorosis is universal along coastal zones, and the seawater or brine water intrusion is occasionally supposed to enrich groundwater fluorine levels. However, there is no conclusive proof, and the laws and mechanisms remain ambiguous. Granite, the common fluorine-bearing rock, is selected and experimented upon to reveal the characteristics and laws of fluorine's leaching ability during the intrusion of seawater. The fluorine-leaching ability increases with the increasing ratios of seawater or brine water, the increasing levels of NaCl or NaHCO3, and the decreasing levels of CaCl2. Such results directly confirm that seawater or brine water intrusion, as well as the conditions of higher Na+, HCO3- and lower Ca2+, promotes fluorine-leaching ability from granite. The intensities of SiOSi, SiOFe, SiOAl bonds decrease but those of OH bonds increase with a higher ratio of seawater or brine water, the higher levels of NaCl or NaHCO3, and the lower levels of CaCl2. This indicates the more silicate dissolution and stronger OH-F exchange evoked by seawater or brine water intrusion are responsible for the higher fluorine-leaching from granite. Therefore, the process of seawater or brine water intrusion should be important for the groundwater enrichment dynamics along coastal zones.

The Enrichment Process of Groundwater Fluorine in Sea Water Intrusion Area of Gaomi City, China.

A typical area, Gaomi City in China, was chosen to discuss the enrichment process of groundwater fluorine in sea water intrusion area. The groundwater had fluorine levels of 0.09-10.99 mg/L, with an average concentration of 1.38 mg/L. The high-fluorine groundwater was mainly distributed in the unconsolidated Quaternary sediments, where concentrations in 83.6% of the samples exceeded the national limit of 1.0 mg/L. The groundwater in the Quaternary sediments also had higher levels of Cl- , TDS, Mg2+ , and pH and lower levels of Ca2+ , Co, Ni, and Cu than that in the bedrock. The groundwater fluorine levels in the Quaternary sediments are positively correlated with Cl- , TDS, Mg2+ , pH, and negatively correlated with Ca2+ , γCa2+ /γMg2+ , Co, Ni, Cu. Geochemical indices of Cl- and TDS indicate sea water intrusion in the Quaternary high-fluorine groundwater area (F- > 1.0 mg/L), while they do not indicate any intrusion in the bedrock area. The chemical weathering of minerals was intensified with the intrusion of sea water. Cation exchange was confirmed to occur in the Quaternary sediments and was promoted by sea water intrusion. Cation exchange consumes part of groundwater Ca2+ and permits more F- dissolving. Consequently, in the Quaternary sediments, the groundwater was supersaturated with CaF2 minerals and undersaturated with MgF2 minerals when F- > 1.0 mg/L, while CaF2 and MgF2 minerals both are undersaturated when F- < 1.0 mg/L. Thus, the chemical weathering of minerals and cation exchange caused by sea water intrusion are the crucial processes controlling the groundwater fluorine levels, which should be considered when the groundwater fluorine enrichment mechanism is discussed along coastal zones.

The Enrichment Process of Groundwater Fluorine in Seawater Intrusion Area of Gaomi City, China.

A typical area, Gaomi City in China, was chosen to discuss the enrichment process of groundwater fluorine in seawater intrusion area. The groundwater had fluorine levels of 0.09-10.99 mg/L, with an average concentration of 1.38 mg/L. The high-fluorine groundwater was mainly distributed in the unconsolidated Quaternary sediments, where concentrations in 83.6% of the samples exceeded the national limit of 1.0 mg/L. The groundwater in the Quaternary sediments also had higher levels of Cl- , TDS, Mg2+ , pH and lower levels of Ca2+ , Co, Ni, Cu than that in the bedrock. The groundwater fluorine levels in the Quaternary sediments are positively correlated with Cl- , TDS, Mg2+ , pH, and negatively correlated with Ca2+ , γCa2+ /γMg2+ , Co, Ni, Cu. Geochemical indexes of Cl- and TDS indicate seawater intrusion in the Quaternary high-fluorine groundwater area (F- > 1.0 mg/L), while they do not in the bedrock area. The chemical weathering of minerals was intensified with the intrusion of seawater. Cation exchange was confirmed to occur in the Quaternary sediments, and was promoted by seawater intrusion. Cation exchange consumes part of groundwater Ca2+ and permits more F- dissolving. Consequently, in the Quaternary sediments, the groundwater was super-saturated with CaF2 minerals and under-saturated with MgF2 minerals when F- > 1.0 mg/L, while CaF2 and MgF2 minerals both are under-saturated when F- < 1.0 mg/L. Thus, the chemical weathering of minerals and cation exchange caused by seawater intrusion are the crucial processes controlling the groundwater fluorine levels, which should be considered when the groundwater fluorine enrichment mechanism is discussed along coastal zones. This article is protected by copyright. All rights reserved.