Date of Award

12-2009

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

Advisor

Aria Amirbahman

Second Committee Member

Stephen Norton

Third Committee Member

Ivan Fernandez

Abstract

Eutrophication of Maine Lakes has deleterious effects on water quality. The recovery time of affected lakes is increased by the internal cycling of nutrients. Phosphorus (P) is the limiting nutrient in many of Maine lakes so that the fate of this element is of primary concern. Lake sediments are a source of bioavailable P to the water column when the hypolimnion becomes anoxic. This study examines the biogeochemical processes occurring in lake sediments that lead to P release and sequestration. The investigative methods used were water column monitoring, sediment solid phase analysis, and sediment pore-water analysis. The goal was to measure temporal changes in each of these compartments to elucidate the main mechanisms related to internal P cycling. The results of this study show that the reductive dissolution of Fe (oxy)hydroxides and associated P is the main driver of sedimentary P release. During oxic periods in the hypolimnion, solubilization processes deeper in the sediments supply the oxycline at or near the sediment-water interface (SWI) with a large reservoir of inorganic P. These processes are controlled by Fe(III) reducing bacteria, mineralization of organic P, and desorption of P from sediment solid phases. In eutrophic lakes, P solubilization processes occur closer to the SWI throughout the year and the zones of production are larger due to increased sedimentation. Once the hypolimnion becomes sufficiently anoxic, the accumulated P at the SWI is released into the water column with a large initial efflux that steadily declines as P accumulates in the hypolimnion. P nuclear magnetic resonance data provide evidence that at least part of this sedimentary efflux is a result of the rapid decomposition of organic P, but compared to the reductive dissolution of Fe (oxy)hydroxides, this mechanism is relatively minor. P burial mechanisms in Maine lake sediments are related to the precipitation of vivianite [Fe3(PO4)2] and possibly hydroxyapatite [Ca10(PO4)6(OH)2] along with the permanent adsorption to aluminum hydroxide [Al(OH)3]. Finally, a paleolimnological investigation provided evidence that the recent eutrophication of a shallow pond is caused by the supply and recycling of P rather than trophic cascade effects.

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