Evaluation of the sources and cycles of water quality contaminants in watersheds is critical for effective surface water resource management. In particular, iron (Fe) and manganese (Mn), commonly found in rocks and sediments, have adverse impacts on water quality. However, controlling Fe and Mn in surface water systems is often complex and requires careful consideration of the hydrologic and biogeochemical factors that influence the speciation and mobility of these metals.
This dissertation investigates the sources and cycles of Fe and Mn in surface waters designated for human use. Here, I present the findings from three field- and laboratory-based studies conducted at sites in western Virginia, United States. The first study examines the impacts of reservoir-derived and watershed-derived metals on water quality along the 180 km reach of the Roanoke River downgradient from Leesville Dam. The results from this study showed strong temporal influences on river water quality immediately downgradient of the dam, resulting from seasonal reservoir dynamics. Further downgradient in the Roanoke River, water quality was strongly tied to hydrologic conditions resulting from influences generated in the watershed. The second study investigated the effects of increasing dissolved oxygen (DO) concentrations in the hypolimnion of stratified drinking water reservoir on Fe and Mn oxidation and removal. Results from a whole-ecosystem experiment showed that increasing DO concentrations through hypolimnetic oxygenation was effective for preventing the accumulation of soluble Fe in the water column. Although Mn oxidation increased under well-oxygenated conditions, soluble Mn still accumulated in the hypolimnion. Results from a laboratory experiment demonstrated that the oxidation of Mn was strongly tied to the activity of Mn oxidizing microbes. The third study examined the relative contribution of external and internal metal loadings to the exchange of metals between sediments and the water column and the source/sink behavior of a seasonally stratified reservoir under varying hydrologic conditions in the inflows and outflows and redox conditions in the reservoir hypolimnion. Results from this study showed that redox conditions strongly influenced the exchange of metals between the sediment and aqueous phase, but had little effect on the source/sink behavior of the reservoir, while external tributary loadings had little effect on internal redox cycles, but was a strong indicator for whether the reservoir behaved as a net metal source or sink. Overall, the findings from these studies exemplify the value of characterizing the hydrologic and biogeochemical drivers of Fe and Mn cycles for managing the water quality effects of these metals in surface water supplies. / Ph. D. / Identifying where drinking water contaminants come from and how they change in river, lake, and reservoir environments is critical for effectively managing surface water resources. In particular, the metals iron (Fe) and manganese (Mn), which are commonly found in rocks and sediments, can pose water quality problems. Controlling Fe and Mn in surface waters requires knowledge of flow conditions and water chemistry, which can both influence how these metals are transported and whether they will reach problematic levels.
This dissertation investigates the sources and chemical cycles of Fe and Mn in surface waters designated for human use. Here, I present the findings from three fieldand laboratory-based studies conducted at sites in western Virginia, United States. The first study examines temporal and spatial patterns of Fe and Mn concentrations along the 180 km reach of the Roanoke River downstream from Leesville Dam. The results from this study showed that the chemistry of Leesville Lake, which varies seasonally, is an important influence on the concentration of Fe and Mn in the river just downgradient from the dam. Further downstream in the Roanoke River, metal concentrations in the river were strongly tied to flow conditions in the streams that originate in the watershed and flow into the Roanoke River. The second study investigated the effects of increasing dissolved oxygen (DO) concentrations in a drinking water reservoir on the chemical oxidation and removal of Fe and Mn in the reservoir. Results from a whole-ecosystem experiment showed that increasing DO concentrations in the reservoir using an oxygenation system was effective for preventing the accumulation of dissolved Fe in the water column. Although Mn oxidation increased under when DO concentrations were high, soluble Mn remained problematic in the reservoir. Results from a laboratory experiment demonstrated that the oxidation of Mn was strongly tied to the activity of Mn oxidizing microbes. The third study examined the effects of DO concentrations in a drinking water reservoir and flow conditions in the major stream flowing into the reservoir on the transfer of Fe and Mn between the reservoir water and sediments. We also examined how stream discharge and DO concentrations in the reservoir influenced the net transfer of metals into or out of the reservoir. Results from this study showed that DO concentrations strongly influenced the transfer of metals between the reservoir water and sediment, but had little effect on the net transfer of metals into or out of the reservoir, while flow conditions in the inflow stream had little effect on metal transfer between the reservoir water and sediments, but was a strong indicator for whether there was a net transfer of metal into or out of the reservoir. Overall, the findings from these studies exemplify the value of characterizing the hydrologic and biogeochemical conditions that effect Fe and Mn for managing water quality in drinking water supplies.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/82347 |
| Date | 01 September 2016 |
| Creators | Munger, Zackary William |
| Contributors | Geosciences, Schreiber, Madeline E., Carey, Cayelan C., Rimstidt, J. Donald, Godrej, Adil N. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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