Title page for ETD etd-03312010-111229

Type of Document Dissertation
Author Bryant, Lee Davis
Author's Email Address lebryan1@vt.edu
URN etd-03312010-111229
Title Dynamic forcing of oxygen, iron, and manganese fluxes at the sediment-water interface in lakes and reservoirs
Degree PhD
Department Civil Engineering
Advisory Committee
Advisor Name Title
Little, John C. Committee Co-Chair
Wueest, Alfred Committee Co-Chair
Berg, Peter Committee Member
Eick, Matthew J. Committee Member
McGinnis, Daniel F. Committee Member
Vikesland, Peter J. Committee Member
  • oxygenation
  • manganese
  • iron
  • diffusive flux
  • turbulence
  • Sediment
  • water
Date of Defense 2010-03-23
Availability unrestricted
The National Research Council recently called for a more interdisciplinary approach to drinking water research to address the critical issue of global drinking water supplies. Hypolimnetic oxygenation systems (HOx) are being increasingly used to improve water quality in stratified reservoirs by increasing dissolved oxygen (O2) concentrations and subsequently suppressing the release of soluble species such as iron (Fe) and manganese (Mn) from the sediment into the water. However, while the influence of HOx on the water column has been established, little work has been done on how oxygenation affects sediment O2 uptake (i.e., sediment oxygen demand) and other sediment-water fluxes. In response to the growing need for alternative approaches for improving water quality, we conducted highly interdisciplinary research to evaluate how O2, Fe, and Mn cycling at the sediment-water interface is influenced by both natural and HOx-induced variations in water column dynamics, chemical redox processes, and microbial activity within the sediment, all of which may govern sediment-water fluxes. Studies were performed in an alpine lake in Switzerland and in an HOx-equipped drinking-water-supply reservoir in Virginia. This research was based on in situ field campaigns paired with laboratory experiments, microbial analyses, and computer simulation to elucidate variable sediment O2 uptake and corresponding Fe and Mn cycling. This work is unique in that sediment-water fluxes were assessed using in situ data from both sides of the sediment-water interface.

Results show that sediment O2 uptake flux is strongly controlled by both wind- and HOx-induced dynamic forcing. Our findings reveal that Fe and Mn fluxes were suppressed from the bulk hypolimnion via biogeochemical cycling in the oxic benthic region. Results also indicate that the sediment microbial community structure may directly respond to HOx-induced variation in sediment O2 availability. Additionally, based on an analysis of the robustness of several commonly used methods for flux calculations, we show that flux estimates are not strongly dependent on the method chosen for analysis. Ultimately, by emphasizing the highly transient nature of sediment O2 uptake, this research will aid in accurate characterization of various sediment-water fluxes and corresponding water quality. Our results will also directly contribute to the optimization of HOx operations and lake and reservoir management.

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