13:45 〜 15:15
[HTT15-P08] Lithium and boron characteristics of shallow coastal groundwater on Saijo Plain, Ehime Prefecture
キーワード：地下水、塩水化、微量元素
Groundwater is used for many purposes including agriculture and industry as well as potable water. Because degradation of groundwater quality threatens their stationary availability, public health, and the environment, we must monitor its changes from various chemical components to detect introduced chemical contaminants originated from anthropogenic and natural sources. Among natural contaminants into groundwater system, one major potential risk is the influence of saline intrusion in a coastal aquifer, which can result in abandonment of freshwater supply.
In this study, Li and B dissolved in groundwater are used for a sensitive detection of the salinization front. Concentrations of both elements are high in seawater and quite low in shallow groundwater. Their natural isotopic variation is about 65 ‰ for δ7Li and about 90 ‰ for δ11B with the highest values observed in seawater. Therefore, the contribution of seawater-derived components to shallow coastal groundwater can be detected more sensitively than the main constituents by of Li and B concentrations and their isotopic ratios.
To evaluate the extent of salinization, Li and B of were measured in a shallow coastal groundwater area on Saijo Plain, Ehime Prefecture. From 13 wells, water temperature, pH, electrical conductivity, redox potential, and dissolved oxygen were measured at the sites, and Li and B concentrations were determined by ICP-MS. In addition, Li isotope ratios were measured using double-focus multiple-collector ICP-MS after chemical purification.
The resultant concentrations of Li and B ranged 0.9-1.7ppb for Li and 13-34ppb for B except one point of 65 ppb B. These concentrations tended to be slightly higher in the coastal wells, suggesting that the concentrations of Li and B may be influenced by seawater-derived components. Li isotope analysis showed that one coastal well with high Li and B concentrations had δ7Li value of +34 ‰, which was higher than that of seawater (+31 ‰), and the influence of seawater-derived components was suggested. The δ7Li of wells near the Kamo River, a major river flowing through the Saijo Plain, is low at +22 ‰ and gradually increases toward the coastal area. These data suggest that water recharged from the Kamo River contributes to the groundwater in Saijo Plain as well as seawater-derived components.
In this study, Li and B dissolved in groundwater are used for a sensitive detection of the salinization front. Concentrations of both elements are high in seawater and quite low in shallow groundwater. Their natural isotopic variation is about 65 ‰ for δ7Li and about 90 ‰ for δ11B with the highest values observed in seawater. Therefore, the contribution of seawater-derived components to shallow coastal groundwater can be detected more sensitively than the main constituents by of Li and B concentrations and their isotopic ratios.
To evaluate the extent of salinization, Li and B of were measured in a shallow coastal groundwater area on Saijo Plain, Ehime Prefecture. From 13 wells, water temperature, pH, electrical conductivity, redox potential, and dissolved oxygen were measured at the sites, and Li and B concentrations were determined by ICP-MS. In addition, Li isotope ratios were measured using double-focus multiple-collector ICP-MS after chemical purification.
The resultant concentrations of Li and B ranged 0.9-1.7ppb for Li and 13-34ppb for B except one point of 65 ppb B. These concentrations tended to be slightly higher in the coastal wells, suggesting that the concentrations of Li and B may be influenced by seawater-derived components. Li isotope analysis showed that one coastal well with high Li and B concentrations had δ7Li value of +34 ‰, which was higher than that of seawater (+31 ‰), and the influence of seawater-derived components was suggested. The δ7Li of wells near the Kamo River, a major river flowing through the Saijo Plain, is low at +22 ‰ and gradually increases toward the coastal area. These data suggest that water recharged from the Kamo River contributes to the groundwater in Saijo Plain as well as seawater-derived components.