Phosphorus Cycling in the Earth Critical Zone
Phosphorus biogeochemical cycling in the Earth Critical Zone shapes ecosystem structure and function, and affects agricultural productivity. Much has been learned regarding C and N cycling but less for P cycling regarding 1) the biological, chemical, and physical factors regulating P transformations in soils; 2) its interaction with the cycling of N and C; 3) how it is affected by ongoing climate change, and by human perturbation, such as changes in land use and cover; and 5) how to improve P use efficiency in agriculture. Our research is to address some aspects of these grand challenges by conducting both field and laboratory studies and using X-ray absorption and 31P NMR spectroscopy and isotopic techniques. The current projects including: 1) Phosphorus transformation during ecosystem development and effects of aeolian dust input; 2) Phosphorus speciation and vertical distribution in soil profiles across environmental gradients (climate and substrate age); and 3) Phosphorus speciation in aeolian dust and its solubility and availability in alpine lakes or humid tropical rainforest of South America.
Structure, Reactivity, Formation and Transformation of Biotic and Abiotic 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.
- Sulfate, Phosphate and Silicate Chemistry at
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).