Radium Isotopes
The finding of high radium activities in low-saline and oxygenated groundwater that we found in Jordan (Ra_Jordan_EST), raises the question for the role of salinity in radium mobilization. The literature indicates that radium desorption is positively correlated with water salinity, yet other factors – such as the redox state and temperature – may also affect Ra mobilization. We have conducted several studies along salinity and water chemistry transects in groundwater systems from the Piedmont in North Carolina (Ra_North Carolina), sea water intrusions along the coastal aquifers of North Carolina , Israel, and Morocco, alluvial basin in Arizona (Arizona_paper) and from groundwater deep sandstone aquifers in Minnesota. Overall, these studies are designed to reveal the net effects of each of these geochemical factors on radium mobilization and also aim to provide geochemical tools for prediction the relationships between salinization phenomena and radium occurrence.
In addition to the study of radium mobilization, we have explored the potential of using radium isotopes for quantifying groundwater discharge into low-saline surface water. Radium isotopes have been used to detect the subsurface groundwater discharge (SGD) into coastal and estuarine systems, where it is assumed that Ra behaves conservatively in saline water (i.e., no adsorption). Former graduate student Hadas Raanan has worked on an opposite setting where the saline groundwater discharges into a low-saline lake (Paper in L&O). In such condition, Ra is adsorbed into suspended matter in the water column, but at the same time, the short-lived 224Ra and 223Ra nuclides are generated by recoiled from parent nuclides in the suspended matter. Taking into consideration these effects, we have developed a model that quantifies the flux of the Ra-rich saline groundwater into the Sea of Galilee in Israel . Raanan also conducted adsorption experiments in order to determine the distribution coefficient of Ra adsorption on sediments from the Sea of Galilee and its dependence on the water salinity. In addition, we have measured the Ra distribution in sediments from cores from the bottom of Sea of Galilee. Raanan has developing a technique for the measurement of Ra isotopes by TIMS to be applied for measuring Ra in pore water extracted from these cores.
In addition, we are working on the SGD of low-saline groundwater into low-saline surface water (stream, river) in North Carolina. In spite of Ra retention in low saline conditions, groundwater is significantly enriched in Ra relative to surface water. We use this difference to quantify the SGD into the Neuse River and New Hope Creek in the Piedmont of North Carolina. Following the methods we have developed for the lake system, we hope to establish a new geochemical tool that would provide a reliable measurement of the SGD component in a river system.
