The research group aims to understand biogeochemical and environmental geochemical processes driving elemental cycles at the terrestrial Earth’s surface. We examine biogeochemical processes and cycles of nutrients, carbon, and trace metals in Earth’s critical zone, particularly the soil part, at various spatial and temporal scales. We futher employ laboratory simulations to provide mechanisic understanding for those biogeochemical and environmental geochemcal processes. Currently, the research group primarily works in two reserach areas:
  • Biogeochemical Cycling in Earth's Critical Zone
    Earth's critical zone is the heterogeneous, near surface environment in which complex interactions involving rock, soil, water, air and living organisms regulate the natural habitat and determine the availability of life-sustaining resources. As far as we know, Earth is unique in the level of biological complexity that drives many of the chemical reactions that occur in the critical zone. Life depends on electron transfers that primarily start with solar capture and flow through reaction chains that change the forms of many elements that are otherwise locked in rocks or in dead organic matter. As a consequence, our group focuses on the chemical processes that determine the forms and availability of phosphorus (P), sulfur (S) and carbon (C) compounds, and trace metals. We combine molecular-scale characterization (with synchrotron X-ray techniques, ESI-FTICR mass spectrometry, and NMR spectroscopy) and isotope techniques to understand their chemical speciation, transformation, distribution and availability at ecosystem scales, and to evaluate their responses to climate change and human perturbation (e.g., changes in land use and cover). Along with advanced analytical techniques, we use environmental gradients (soil chrnosequence, climate, weathering profiles) to provide natural experiments designed to understand how the critical zone responds to different forcing functions.

    1) Quantifying uncertainties in sequential chemical extraction of soil phosphorus using phosphorus K-edge XANES spectroscopy (Gu et al., Enviorn. Sci. Technol., 2020)

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    2) Aeolian dust deposition and the perturbation of phosphorus transformations during long-term ecosystem development in a cool, semi-arid environment (Gu et al., Geochim. Cosmochim. Acta, 2019)  

    3) Dust-borne phosphorus geochemistry and its solubility in alpine lakes in the Rocky Mountain area (Zhang et al., Environ. Sci. Technol., 2018)

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  • Structure, Formation and Transformation of Manganese Oxides
    Birnessite minerals are the most common and abundant type of Mn oxides in nature, imposing significant impact on many critical biogeochemical processes owing to their extraordinary sorption and oxidation properties. This project is to determine the impact of an array of environmentally-relevant physiochemical factors on the structure and properties of microbially-produced Mn oxides and chemically-synthetic analogues, and their transformation to other mineral phases, such as tunneled structures.  
  • Mineral-Water Inerfacial Processes
    Oxyanions, such as sulfate, phosphae and silicate, are important nutrients in soils and also play major role in many geochemical processes. Their fate, behavior and bioavailability in the environment is strongly influenced by mineral surfaces on which the adsorb, precipitate and polymerize. Our ongoing projects examine how they react with surfaces of Fe oxides, a group of the abundant and reactive minerals in the environment. The following figures show that phosphate transits from surface complexes to precipitates on ferrihydrite surfacs with increasing P loading (left); silicate transits from monodentate-mononuclear monomers to bidentate-binuclear polymers (right); and sulfate forms both bidentate-binuclear inner-sphere and outer-sphere complexes (bottom).