Date of Award

2021

Document Type

Honors Thesis (Open Access)

Department

Colby College. Chemistry Dept.

Advisor(s)

D. Whitney King

Second Advisor

Denise Bruesewitz

Third Advisor

Benjamin Twining

Abstract

The internal recycling phosphorus in freshwater lake bottom sediments represents a significant source of hypolimnetic phosphorus (P) release for many of Maine’s lakes. In summer months, Maine lakes often thermally stratify and the lake hypolimnion develops anoxia, leading to a reduction in redox potential at the sediment-water interface. These reducing conditions facilitate the reductive dissolution of ferric iron, and, since phosphorus is often present in freshwater lake sediments as solid FeOOH-PO4 complexes, results in release of soluble phosphorus into the water column. Our current study presents field and laboratory data from sediment fractionation extractions designed to quantify concentrations of iron, aluminum and phosphorus in lake bottom sediments from East Pond (Smithfield, ME), Great Pond (Belgrade, ME) and China Lake (China, ME). We focus on elucidating the chemical foundations of the fractionation method so as to streamline our extraction procedure and minimize the required sample size. We confirm that internal P flux is negligible during hypolimnetic anoxia if molar Al:Fe is > 3. We ultimately hope to apply our extraction data to optimize aluminum dosing schemes designed to mitigate internal P flux in lakes above their phosphorus sorption threshold using the designated Al:Fe > 3 as an operational target for aluminum additions.

Keywords

biogeochemistry, phosphorus cycling, sediment fractionation, algal bloom, water quality, aluminum dosing

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