Stable Isotope-Enabled Hydrogeochemistry
Water-mineral interactions are a fundamental control on ecosystem water availability and quality, the fate and transport of pollutants in the subsurface, and the weathering of minerals into soils and sediments. Understanding these interactions are therefore important to understanding how water interacts with and influences larger scale systems. I use the stable isotopes of water to probe processes happening at the water-mineral interface, which is hard to observe otherwise.
Water-mineral interactions are a fundamental control on ecosystem water availability and quality, the fate and transport of pollutants in the subsurface, and the weathering of minerals into soils and sediments. Understanding these interactions are therefore important to understanding how water interacts with and influences larger scale systems. I use the stable isotopes of water to probe processes happening at the water-mineral interface, which is hard to observe otherwise.
The relationship of shifts in the 18O composition of soil water in mixtures of Mg-, Ca-, K-, Na-treated montmorillonite and water to gravimetric water content (Oerter et al., 2014, Journal of Hydrology).
Oxygen isotope 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.
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.
Oerter, E, K Finstad, J Schaeffer, G Goldsmith, T Dawson, R Amundson, 2014, Oxygen isotope fractionation effects in soil water via interaction with cations (Mg, Ca, Na, K) adsorbed to phyllosilicate clay minerals. Journal of Hydrology, v. 515, p. 1-9. pdf pdfdf
Isotope hydrogeochemistry of hyper-saline and salt-saturated aqueous solutions
Oerter, E, M Singleton, L Davisson, 2018, Hydrogen and oxygen stable isotope dynamics of hyper-saline and salt-saturated aqueous solutions, Geochimica et Cosmochimica Acta, v. 238, p. 316-328.
Oerter, E, M Singleton, L Davisson, 2018, Hydrogen and oxygen stable isotope dynamics of hyper-saline and salt-saturated aqueous solutions, Geochimica et Cosmochimica Acta, v. 238, p. 316-328.
Pioneering the field of stable isotope mineral hydration hydrology
I have developed ways to couple thermogravimetry (precise heating and weighing) with laser isotope analysis to measure the isotopic composition of mineral hydration water. For example, we used this approach to make the first measurements of goethite (FeO(OH)) hydration waters, which has important implications for paleoclimate records based on iron oxides, a wide research field.
Oerter, E, M Singleton, L Davisson, 2017, Hydrogen and oxygen stable isotope signatures of goethite hydration waters by thermogravimetry-enabled laser spectroscopy. Chemical Geology, v. 475, p. 14-23
And in hydrated uranium oxides, important materials in nuclear forensics and nuclear material storage:
Oerter, E, M Singleton, Z Dai, M Thaw, L Davisson, 2019, Hydrogen and Oxygen Stable Isotope Composition of Water in Metaschoepite Mineralization on U3O8, Applied Geochemistry, v. 112, 104469,
https://doi.org/10.1016/j.apgeochem.2019.104469
I have developed ways to couple thermogravimetry (precise heating and weighing) with laser isotope analysis to measure the isotopic composition of mineral hydration water. For example, we used this approach to make the first measurements of goethite (FeO(OH)) hydration waters, which has important implications for paleoclimate records based on iron oxides, a wide research field.
Oerter, E, M Singleton, L Davisson, 2017, Hydrogen and oxygen stable isotope signatures of goethite hydration waters by thermogravimetry-enabled laser spectroscopy. Chemical Geology, v. 475, p. 14-23
And in hydrated uranium oxides, important materials in nuclear forensics and nuclear material storage:
Oerter, E, M Singleton, Z Dai, M Thaw, L Davisson, 2019, Hydrogen and Oxygen Stable Isotope Composition of Water in Metaschoepite Mineralization on U3O8, Applied Geochemistry, v. 112, 104469,
https://doi.org/10.1016/j.apgeochem.2019.104469