Thesis (M.S.)--Oregon State University, 1981. / Typescript (photocopy). Includes bibliographical references (leaves 13-14). Also available on the World Wide Web.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed on Feb. 8, 2007). PDF text: v, 157 p. : ill. (some col.). UMI publication number: AAT 3216347. Includes bibliographical references. Also available in microfilm and microfiche format.

Thesis (Ph. D.)--Oregon State University, 1981. / Typescript (photocopy). Includes bibliographical references (leaves 167-178). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 1977. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Three experiments were conducted to study dietary effects on urea-nitrogen (N) recycling as a strategy to improve the efficiency of N utilization in ruminants. Experiment 1 examined the effects of feeding diets containing two levels of dietary crude protein (CP; 10.8 vs. 14.0%) and ruminally-degradable protein (RDP; 73.4 vs. 76.0% of CP) on urea-N recycling to the gastro-intestinal tract (GIT), N balance, and microbial protein production in beef heifers. Feeding the low CP diet decreased N intake (P < 0.01), ruminal ammonia-N (NH3-N) concentration (P < 0.01) and urinary N excretion (P <0.01). Endogenous urea-N production increased (P = 0.03) with increasing dietary CP level, as did urinary urea-N loss (P = 0.04). However, urea-N transfer to the gastro-intestinal tract (GIT) was similar across diets, with most of this N returned to the ornithine cycle. Microbial N supply was unaffected (P > 0.05) by dietary treatment. Experiment 2 examined the effects of feeding diets containing two levels of ruminally-degradable starch (RDS; 28.6 vs. 69.2% of total starch) and RDP (48.0% vs. 55.0% of CP) on urea-N recycling to the GIT, N balance, duodenal nutrient flow, and ruminal microbial protein production in beef heifers fed low CP (10%) diets. Ruminal NH3-N concentration was greater (P = 0.01) in heifers fed high RDP as compared with those fed low RDP, and it was also greater (P = 0.01) in heifers fed low RDS as compared with those fed high RDS. Microbial N flow to the duodenum increased as RDP level increased on the high RDS diet, but was not affected by RDP level on the low RDS diet (interaction; P = 0.04). Urea-N entry rate and urea-N transfer to the gastro-intestinal tract were similar (P > 0.05) across diets. The amount of recycled urea-N that was incorporated into microbial N increased as RDP level increased on the high RDS diet, but the opposite was observed on the low RDS diet (interaction; P = 0.008). Experiment 3 examined the effects of feeding diets containing two levels of CP (14.9 vs. 17.5%) and RDP (63.0 vs. 69.0% of CP) on urea-N recycling to the GIT, microbial protein production, N balance, omasal nutrient flow, and milk production in lactating dairy cows. Nitrogen intake (P < 0.01) and both urinary N (P < 0.01) and urea-N (P < 0.01) output were greater for cows fed the high compared with those fed the low CP diet. Ruminal NH3-N concentration tended to be greater in cows fed the high than those fed the low CP diet (P = 0.06), and was greater in cows fed high RDP as compared with those fed the low RDP diet (P < 0.01). However, N balance, milk yield, and microbial N supply were unaffected (P > 0.05) by dietary treatment. The proportion of endogenous urea-N that was recycled to the GIT (i.e., GER: UER) was greater (P = 0.02) in cows fed the low CP compared with those fed the high CP diet. In summary, the results of this thesis show that reducing dietary CP level in beef and dairy cattle reduces urinary N excretion whilst maintaining microbial N supply. In addition, judicious combinations of RDP and RDS when feeding low CP diets can potentially enhance the efficiency of microbial N production. These data show that through careful dietary manipulation, overall efficiency of N utilization can be improved leading to a reduction in N excretion into the environment.

Anaerobic ammonium oxidation (anammox) is a pathway that has been known for almost 2 decades, but few studies have investigated its importance in natural groundwaters. This thesis investigated the presence of anammox cells and the groundwater geochemistry of 2 sites (Elmira and Putnam) in southwestern Ontario where groundwaters are contaminated with high levels of nitrate and ammonium. Fluorescence in situ hybridization (FISH) was used to quantify the relative abundance of anammox cells in these waters. Our results showed that anammox cells could be detected in many wells at both sites and that their relative abundance varied between 0.45 and 4.81 % at the Putnam site, whereas it ranged between 0.8 to 8.4 % at the Elmira site. These values are within the same range as those obtained for marine and freshwater environments where anammox cells have been detected. In addition, indirect observations point to the fact that N cycling at the 2 sites might be linked to Fe and Mn reduction, but additional experiments are needed. In summary, our results corroborate the findings of N-labeled microcosm experiments which demonstrated that anammox was an important pathway of N cycling in those groundwaters and molecular analyses that detected important anammox organisms at the same sites.

Northern peatlands play a significant role in the global carbon (C) cycle by functioning as sources of atmospheric methane (CH4). Peatlands are becoming polluted as a result of nitrogen (N) deposition, which is likely to impact CH4 dynamics. This thesis presents research at the Mer Bleue bog (Ottawa, Canada) in the longest known simulated atmospheric nutrient deposition experiment. After 8 years of simulated N (and other nutrient) deposition, activities of microbial communities involved in CH4 cycling have been analyzed in the laboratory and CH4 fluxes measured using chamber techniques in the field. High rates (>10 times ambient deposition) of simulated N deposition decreased CH4 production, and enhanced CH4 oxidation in vitro. However, in situ CH4¬ emissions were greater in the high N plots. I hypothesize that CH4 production is therefore driven by short-lived root exudates in the field, consistent with increased shrub biomass that occurs concomitantly with high N deposition.

Northern peatlands play a significant role in the global carbon (C) cycle by functioning as sources of atmospheric methane (CH4). Peatlands are becoming polluted as a result of nitrogen (N) deposition, which is likely to impact CH4 dynamics. This thesis presents research at the Mer Bleue bog (Ottawa, Canada) in the longest known simulated atmospheric nutrient deposition experiment. After 8 years of simulated N (and other nutrient) deposition, activities of microbial communities involved in CH4 cycling have been analyzed in the laboratory and CH4 fluxes measured using chamber techniques in the field. High rates (>10 times ambient deposition) of simulated N deposition decreased CH4 production, and enhanced CH4 oxidation in vitro. However, in situ CH4¬ emissions were greater in the high N plots. I hypothesize that CH4 production is therefore driven by short-lived root exudates in the field, consistent with increased shrub biomass that occurs concomitantly with high N deposition.

One of the environmental problems today in seas, lakes and streams is eutrophication. This is often caused by nutrients such as phosphorus (P) and nitrogen (N) that leak from agricultural areas. A measure to partly prevent the nutrient discharge is to construct or restore wetlands. In order to control the efficiency of nutrient reduction of existing wetlands in the county, the administrative board in Västra Götaland wants to find different criterias for reference wetlands. These reference wetlands should represent other wetlands and be used in future evaluations of reduction of nutrients and design of constructed wetlands. According to the administrative board in Västra Götaland the reference wetlands should have a catchment area of about 50 hectare consisting of at least 70 % arable land, to represent wetlands created to remove nutrients. The surface area should exceed 0,5 hectare and the inlet-nitrogen concentration should be around 5 mg N-1. This report investigates nitrogen and phosphorus retention in two wetlands, Härstad and Åmot in the county of Västra Götaland, and if they fulfill the criteria of being a reference wetlands. In addition to this, a tracer study was performed in one of these wetlands with the purpose to study the hydraulic efficency. Neither the wetland in Åmot or Härstad achieves the guidelines of about 5 mg N l-1 in the incoming water. Therefore, they can be seen as inappropriate as reference wetlands according to their nitrogen retention. The wetland of Härstad, however, has significantly better N retention than the wetland of Åmot. Results from the report shows that N retention in the wetland of Härstad was relatively high not only due a higher N load, but also due to that N was largely in the form of NO3- facilitating efficient transformation of NO3- to N2 by denitrification bacteria. Nitrogen removal was much lower in the wetland in Åmot due to that N in incoming water was not in the form of NO3- and could therefore not be efficiently transformed to N2 by denitrification. Incoming total phosphorus to the Härstad and Åmot wetlands exceeded 100 µg P l-1, which means "extremely high" tot-P concentrations according to environmental quality criteria from the Swedish Environment Protection Agency. Phosphorus load per wetland area was slightly higher in the wetland in Åmot than in the Härstad wetland. In spite of this, P retention per wetland area as well as relative P retention was clearly higher in the Härstad wetland. This can be explained by that P in incoming water to the Härstad wetland was to a larger degree than in the Åmot wetland bound to particles, facilitating P retention through sedimentation. According to the tracer study, the Härstad wetland has a hydraulic efficency (λ) of about 0,13 which means it has a low hydraulic efficiency. The effective volume ratio (e) in Härstad was calculated to 18 % which means that the water has an inadequate spreading in the wetland, which is not good for the nutrient elimination in this wetland. This study illustrates the difficulties in finding representative reference wetlands due to potential differences between wetlands in nutrient concentrations in incoming water, the degree that incoming P is bound to particles, the degree that incoming N is in the form of NO3-, and hydraulic efficiency.