Oxygen isotope fractionation effects in soil water
via interaction with soil mineral particles
In isotope-enabled approaches to hydrology, the soil matrix is typically assumed to be inert with respect to the water oxygen isotopes in the system. We show that Mg, and Ca ions adsorbed to clay minerals exert an effect on the water molecules nearby that tends to concentrate the H2O molecules with an 18O atom around each metal ion, while K ions tend to attract 16O. Our report is the first observation and quantification of this effect and raises the notion that this effect may be present in natural soils that have high clay contents and high cation concentrations. This effect may be a mechanism to explain unusual soil water isotope and ecohydrologic behavior observed in many instances.