SusChEM: Redox and mineral controls maximizing Phosphorus mobility and bioavailability

University Of Vermont & State Agricultural College, Burlington VT

Investigators

Abstract

Understanding phosphorus (P) behavior in the environment is critical to society, as P often plays a central role in promoting productive agriculture as a fertilizer. Yet phosphorus is also a contaminant in aquatic environments, where human-derived enrichment of P in water and sediment can promote harmful algal blooms. Worldwide reserves of P are limited, especially in the U.S., and sustaining agricultural production will require the recovery and recycling of P. The protection of water resources is also an increasingly critical area of concern to promote sustainable clean drinking water, healthy fisheries, and economically vital recreational resources. These issues require improved understanding of how P is, and can be, mobilized in different geological and engineered settings. P interaction with other elements, especially iron, manganese, and carbon, often controls P mobility, and understanding this interaction is therefore key to developing strategies for more sustainable agriculture and water quality. This research program?s goal is to develop a conceptual framework of the environmental conditions that maximize phosphorus mobility in sediment-water systems. The project will integrate with NSF-EPSCoR program investigating lake water quality. Research on these topics will be integrated with outreach opportunities to teach local schoolchildren and stakeholders about responsible nutrient management and how to better protect water resources. Phosphorus is generally partitioned in sediment-water systems between mineral, dissolved, and organic pools. Determining the response times for different pools of P species to changing redox conditions is a major hurdle in understanding the drivers of phosphorus mobility and bioavailability in sediment-water systems. Static models describing P partitioning and mobility between these pools are voluminous but do not capture key factors. The redox conditions near the sediment-water interface (SWI) are a critical control on the reactivity of P and associated redox-active elements (Fe, Mn, S, N especially) in shallow freshwater and marine systems, and can fluctuate on diel, seasonal, and more chaotic event-based timescales. The central hypothesis of this project is that the mobility of specific P pools is maximized by changes in redox conditions at the SWI over short (minutes to hours) time spans, and that the duration and severity of these redox oscillations drives the partitioning and behavior of P (and Fe) species over time near the SWI. To test this requires a comprehensive investigation of P speciation and mobility that couples field and laboratory approaches designed to elucidate the drivers and dynamics of this complex system. Analysis of the specific P pools and related elements will utilize advanced techniques to examine the partitioning of different P forms in different pools under changing redox conditions. Specifically, high-resolution in-situ monitoring of natural and manipulated SWI redox dynamics using environmental voltammetric techniques, combined with a suite of targeted analyses to describe the redox-driven evolution of sediment-water P pools including: 1) sediment P mineralogical composition and extractability, 2) P and Fe speciation, and 3) enzyme digestion and NMR techniques to determine organic P speciation will provide the data needed to develop a molecular-based and temporally constrained model of P speciation and mobility in sediment-water systems.