Earth’s shallow subsurface, or “critical zone,” is of fundamental importance for supporting terrestrial life and maintaining water quality. A vital part of the critical zone is the unsaturated region located nearest to the surface. This zone is also most likely to be affected by future global change due to altered rainfall patterns and evapotranspiration rates across the globe. In order to predict how long-term variations in the water budget will impact nutrient and carbon cycling it is necessary to evaluate the influence of water saturation on mineral weathering reactions. The objective of the proposed research is to elucidate the fundamental mechanisms governing reaction rates as a function of water availability from the molecular to macro scale. This will be achieved through a combination of experimental studies, geochemical modelling, and analytical techniques. Experimental results will lead to the development of a mechanistic reactive transport model that can better predict reaction rates as a function of water saturation. This research has significant implications for the maintenance of a sustainable nutrient supply for natural and agricultural vegetation, the carbon cycle, and remediation of groundwater resources, issues critical to the long-term sustainable growth of our society.
Specific Projects
Mineral precipitation and dissolution under water-limited conditions
Element and nutrient fluxes are commonly considered to depend on the wetted surface area of mineral phases. Yet, the definition of “wetted surface area” is not straightforward. Experiments are being conducted in the laboratory under extremely water-limited conditions to better answer the question: "How much water is enough water for minerals to react?"
Impact of repeated evaporation and rainfall patterns on element release
Mineral dissolution and precipitation reactions are key processes that dictate the release and uptake of elements including nutrients, contaminants, and carbon in both natural (e.g., soils) and disturbed (e.g., mine tailings) environments at the Earth's surface. Rainfall and evaporation processes can impact the release of elements via physical and chemical alteration of the porous medium, for example due to physical movement of particles, and dilution or concentration of solutes. We aim to elucidate how repeated wetting and drying events alter element fluxes from unsaturated media, and thus better predict how nutrient and element cycles may respond to global-scale changes in rainfall, evaporation, and soil moisture patterns.
Fractionation of stable isotopes in weathering environments
Fractionation of stable isotopes provides insights into processes occurring during mineral weathering and secondary mineral formation. The fractionation of so-called "non-traditional" stable isotopes such as isotopes of alkaline earth metals (e.g., Ca, Mg) in particular can provide information regarding weathering fluxes and precipitation of carbonate minerals that store CO2. As such, a new direction of DryMIN involves the investigation of the controls on the fractionation of Ca and Mg isotopes between solution and solid carbonate minerals including the Ca-carbonate mineral, calcite, and the Mg-carbonate mineral, nesquehonite.
Publications
Publications resulting so far from this project, or from collaborations on this project are shown below. Please note, the supplied documents represent the manuscripts before final proofing; some changes may be present relative to the formatted, published version. Harrison A.L., Mavromatis, V., Oelkers, E.H., and Bénézeth, P. (2019) Solubility of the hydrated Mg-carbonates nesquehonite and dypingite from 5 to 35°C: Implications for CO2 storage and the relative stability of Mg-carbonates. Chem. Geol. 504: 123–135.
Rigopoulos, I., Harrison, A.L., Delimitis, A., Ioannou, I., Efstathiou, A.M., Kyratsi, T., and Oelkers, E.H. (2018) Carbon sequestration via enhanced weathering of peridotites and basalts in seawater. Appl. Geochem. 91: 197–207.
Mavromatis, V., Harrison, A.L., Eisenhauer, A., and Dietzel, M. (2017) Strontium isotope fractionation during strontianite (SrCO3) dissolution, precipitation, and at equilibrium. Geochim. Cosmochim. Acta. 218: 201–214