Thesis (Ph. D.)--Ohio State University, 2004. / Document formatted into pages; contains xiii, 234 p. Includes bibliographical references. Abstract available online via OhioLINK's ETD Center; full text release delayed at author's request until 2005 June 1.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (doctoral)--Technische Universiteit Delft, 1997. / Includes bibliographical references.

Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2009. / Committee Chair: Ellery Ingall; Committee Member: Andrew Stack; Committee Member: Greg Huey; Committee Member: Joseph Montoya; Committee Member: Judith Curry.

Thesis (M.S.)--California Polytechnic State University, 2009. / Mode of access: Internet. Title from PDF title page; viewed on May 22, 2009. Major professor: Nirupam Pal, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Civil and Environmental Engineering." "March 2009." Includes bibliographical references (p. 88-90). Also available on microfiche.

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [147]-165).

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 93-102).

Carbon (C) as a driver of soil denitrification was investigated in a series of four laboratory incubation experiments employing stable nitrogen (N) and C isotope approaches. The research addressed the lack of knowledge on mechanisms through which the quantity and quality of organic‐C containing substrates interact with denitrification. The amount of organic matter added to soil was manipulated to relate C respiration with process rates of denitrification. Respiration derived from dissolved organic matter C was linearly related to denitrification but the direction of the relationship was variable in time. This may be most likely an effect of changing quality of the C available and possibly microbial community structure. Nitrous oxide (N2O) emission from denitrification at the later stages of residue decomposition was driven by nitrate (NO3‐) accumulation in the soil rather than C provided by the residue. Denitrification across a vertical shallow soil profile formed in a laboratory microcosm was investigated. A surface hotspot formed immediately as a response to residue‐C addition and increased rates of N2O production. N2O reduction occurred at depth. The hotspot at depth was related to an indirect effect of residue‐C, which was depletion of O2. Further, to address the complexity of low molecular weight C substrate available to denitrifiers in the soil solution, denitrification rates in response to glucose, citric acid and glutamic acid supplied individually versus in mixture were characterised. Carbon substrate quality regulated N2O production rates via interactions within the soil microbial community and with the soil solid phase. Overall, the experiments showed that C stimulates strong N2O emission peaks and increase cumulative N2O emissions from arable soil along a gradient of varying C substrate complexity and quantity. Interaction in space and time play an important role when C containing inputs affected other proximal drivers of denitrification such as NO3‐ and O2.

The application of nitrogen (N) fertilizers and manure to agricultural soil is essential for crop production, but has in turn introduced environmental impacts including: eutrophication, contamination of groundwater, freshwater acidification, and an increase in greenhouse gas emissions. The movement of nitrogen was observed following liquid swine manure applications at six fields in Winchester, ON employing controlled tile drainage and denitrifying bioreactors. The manure was mainly in the form of ammonium during application where it was transformed to other N species including nitrate and nitrous oxide (N2O) by microbial activity in soil. Large soil N2O fluxes occurred in fields throughout 2012 and 2013, and total N of soil in the fields was enriched in 15N, indicating denitrification. Soil nitrate was also leached and collected by drainage tiles, and a portion of the tile water was treated by denitrifying bioreactors. Previous studies have demonstrated that denitrification of nitrate in bioreactors elicits the production of N2O, which is emitted from the overlying soil surface and/or is released as dissolved N2O in tile effluent. In this study, it is found that a decrease in nitrate was associated with decreasing levels of nitrous oxide during a rain event, and no significant N2O flux was recorded above bioreactors throughout either year. The δ15N and δ18O signatures of nitrate did not change significantly following bioreactor treatment and did not exhibit the 15N and 18O enrichment that is characteristic of denitrification. The data demonstrates that the decrease in nitrate through the bioreactors was due to dilution, likely from the accumulation of rainfall in reactor beds employing controlled tile drainage. Further work is needed to examine the conditions under which dilution may occur in place of denitrification.

Wetland systems have been widely studied and found to have enhanced capacity to transform meaningful amounts of nitrate (NO3-N) from shallow subsurface water before the improved-quality water is delivered to lake, river, and groundwater systems. Wetland are characterized by the abundant presence of electron donors and acceptors (i.e., organic carbon & NO3-N, respectively) as well as anoxic and reducing conditions which are crucial for supporting denitrification processes and the reduction of excessive nitrate levels in the environment. When favorable conditions within the wetland systems are not present, denitrification is often limited to the biofilm-protected bacteria hosted on the sediment surfaces. However, there is still a need to determine if floodplain wetlands are being utilized to their maximum potential in excess nitrate removal.