Iron mineral transformations and preservation: Effects of eutrophication-driven changes in sediment geochemistry

Iron (Fe) is an essential nutrient that plays a key role in biogeochemical cycling in aquatic systems. The bioavailability of other essential nutrients, such as phosphorus and silicon, as well as trace metals are intimately coupled to Fe cycling through adsorption and co-precipitation processes in the water column and sediment. Consequently, the dynamics of Fe mineral transformations in sediments regulate the magnitude and timescale of removal of bio-available forms of these elements from water bodies. Laboratory studies have demonstrated that the structure and stability of Fe minerals is affected by the chemical conditions under which they form. However, limited understanding of how this may affect sedimentary Fe cycling under changing environmental conditions remains a critical knowledge gap. This is of particular relevance in light of the growing number of aquatic systems that suffer from eutrophication and hypoxia, which severely alter sediment geochemistry. Here, I propose to study how the dissolution/transformation dynamics and nutrient sorption behavior of major Fe minerals are affected by the sedimentary conditions under which they form. The research will focus on the impact of key dissolved species that show changes in availability in response to eutrophication, such as the nutrients phosphorus and silicon and other important solutes (bicarbonate, iron, sulphate, and sulphide). I will synthesize Fe minerals under different conditions, and investigate (long-term) Fe mineral dissolution and transformation under laboratory and field conditions. I will utilize advanced analytical techniques for characterization of dissolved and solid phase species, in particular diffusive gel techniques and X-ray absorption spectroscopy. These will provide detailed, high-resolution information on Fe mineral dynamics. Quantitative geochemical modeling of mineral (trans)formation and sorption processes will complement the experimental findings. This novel and thorough approach will provide crucial insight into the feedbacks between Fe mineral dynamics and environmental change.