Methane is a potent greenhouse gas with a global warming potential 21 times that of carbon dioxide. Globally, ruminants are the main anthropogenic contributors to methane release to the atmosphere. Methane is produced in the gastrointestinal tract of ruminants, mostly within the rumen by methanogenic archaea. However, methane production represents a loss of 2 to 12% of dietary gross energy for the animal, which could otherwise be available for growth or milk production. Therefore, mitigation of methane production by ruminants could produce both economic and environmental benefits, with more sustainable and energy efficient livestock, and offering a promising way of slowing global warming. Despite extensive research undertaken to find ways of reducing methane emissions from ruminants, progress has been relatively limited. Furthermore, there is still a lack of studies linking rumen microbiology and ruminant nutrition and production. The central purpose of this research was to investigate feed additives to reduce methane emissions and to understand associated changes that occur in the rumen microbiota. For the first experiment (Chapter 2), biochar was evaluated as an antimethanogenic compound for beef cattle. The in vitro gas production technique was used to study the effects of biochar on rumen fermentation and methane production. Overall, methane production was reduced by 5% by the addition of biochar compounds (10 g/kg of substrate). The observed reduction in methane produced was not associated with a change in volatile fatty acid profile suggesting biochar primarily inhibited fermentation. Ammonia concentration was significantly reduced with biochar inclusion. Because different biochars had different effects on methane production, further investigation of relationships between the physicochemical properties of biochars and antimethanogenic effects are necessary. However, due to the small reduction in methane production recorded, research with biochar was discontinued. Encapsulated nitrate was then explored as an antimethanogenic additive and as an alternative non-protein nitrogen source to urea (Chapter 3). The effect of using encapsulated nitrate as a replacement for urea or dietary protein, plus the addition of inorganic sulphur, on enteric methane emissions, nutrient digestibility, nitrogen utilization and microbial protein synthesis from crossbred beef steers were studied. In addition, nitrate toxicity and eating behaviour were investigated. The inclusion of encapsulated nitrate reduced methane production compared to urea and a true protein source, with no adverse effects on rumen fermentation or nitrogen metabolism and no effects with the inclusion of elemental sulphur. The level of addition of encapsulated nitrate (14.3 g nitrate /kg DM) and the time of adaptation chosen for this study (14 days) were adequate to avoid nitrate toxicity. Finally, the effects of adding nitrate inclusion to different basal diets on rumen microbial populations and relationships of these populations with methane production were investigated (Chapter 4). The V4 hypervariable regions of the bacterial and archaea 16S rRNA genes were amplified and sequenced. Effects on microbial population induced by nitrate were dependant on the basal diet but nitrate altered specific archaeal and bacterial OTUs consistently between studies. A direct and strong correlation between some archaea taxonomic groups and OTUs with methane production was observed.

The Occoquan Reservoir is part of the largest indirect potable reuse systems in the United States. It in an important water supply source for the Northern Virginia area, as well as, an ecological and recreational area. Furthermore, the Occoquan Reservoir protects the water quality of the Chesapeake Bay because it acts as a trap for sediments and pollutants. Continuous water quality monitoring and evaluation is critical to preserve this important water resource. Reservoir water quality can be affected by the delivery of pollutants from point and nonpoint sources, potentially causing problems such as eutrophication, excess salinization, presence of compounds that affect human and aquatic health. Different management strategies have been implemented at the Occoquan Reservoir to nutrient loading into the reservoir and address eutrophication issues, including nitrate addition to hypolimnetic waters and installation of a hypolimnetic oxygenation system. The goal of this study is to assess how current management strategies implemented in the Occoquan Reservoir have affected the water quality from 1973 to 2019, with particular emphasis on the data since 2003. This analysis of the Occoquan Reservoir and its tributary watershed includes the evaluation of hydrometeorological data and morphometric characteristics; establishment of long-term trends for water quality constituents; and determination of the trophic state of the reservoir. Data from water samples from four different stations located at the Occoquan Reservoir and four stations located throughout the Occoquan tributary watershed were analyzed for nutrients, principal ions and metals, synthetic organic compounds (SOCs), and other water quality parameters. Long-term water quality trends were determined using Mann-Kendall test and relationship between constituents was evaluated using Principal Component Analysis (PCA). Trophic state of the reservoir was assessed using Carlson's Trophic State Index (TSI), Vollenweider Model, and Rast, Jones, and Lee's Model. Results indicate the Occoquan Reservoir is a eutrophic waterbody. However, the nitrate management strategy and the installation of the hypolimnetic system have improved reservoir water quality, reducing concentrations of nutrients and metals. / Master of Science / The Occoquan Reservoir is part of the largest indirect potable reuse systems in the United States. Indirect potable reuse refers to the planned discharge of reclaimed water into a water supply source, such as a reservoir or lake. The Occoquan Reservoir also serves as an ecological and recreational area, and serves to protects the water quality of the Chesapeake Bay because it acts as a trap for sediments and pollutants. To protect the different ecosystem services that the reservoir provides, it is critical to continuously monitoring and evaluate its water quality. Reservoir water quality can be affected by the delivery of pollutants from industrial and municipal waste discharges (point sources), as well as, from urban and agricultural runoff (nonpoint sources). Contaminants include nutrients (such as nitrogen and phosphorus), ions, metals, and synthetic organic compounds (SOCs) that can affect human and aquatic health. Different management strategies have been implemented at the Occoquan Reservoir to reduce load of pollutants into the reservoir, particularly to reduce concentrations of nutrients, as excessive nutrients can degrade water quality. Two strategies implemented are the addition of nitrogen, in the form of nitrate, and the installation of an oxygenation system at the reservoir bottom waters. The goal of this study is to assess how current management strategies implemented in the Occoquan Reservoir have affected the water quality from 1973 to 2019, with particular emphasis on the data since 2003. This analysis of the Occoquan Reservoir and its tributary watershed includes the evaluation of the hydrological, meteorological, and morphometric characteristics of the Occoquan Reservoir and Watershed; establishment of long-term trends for water quality constituents; and determination of the productivity (trophic state) of the reservoir. Data from water samples from four different stations located at the reservoir and four stations located throughout the watershed were analyzed for nutrients, principal ions and metals, SOCs, and other water parameters indicative of water quality. Statistical analyses were employed to determine long-term water quality trends (Mann-Kendall test) and relationship between constituents (Principal Component Analysis - PCA). The trophic state of the reservoir was assessed using three methods: Carlson's Trophic State Index (TSI), Vollenweider Model, and Rast, Jones, and Lee's Model. Results indicate the Occoquan Reservoir is eutrophic, or highly enriched with nutrients and productive. However, management strategies employed have improved the water quality and the reservoir continues to improve, though at a slow rate.