Thesis (M.S.)--University of Michigan, 1973.

Thesis (M.D.)--University of Pennsylvania, 1808. Includes bibliographical references. / With a half-title. "An inaugural dissertation for the degree of doctor of medicine; submitted to the examination of John M'Dowell, L.L.D. provost, the trustees and medical professors of the University of Pennsylvania, on the twenty-seventh day of April, 1808."--p. [v]. Film 633 reel 6 is part of Research Publications Early American Medical Imprints collection (RP reel 6, no. 144). DNLM Includes bibliographical references.

Graduation date: 1978

Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 53-54).

"An inaugural dissertation for the degree of doctor of medicine; submitted to the examination of John M'Dowell, L.L.D. provost, the trustees and medical professors of the University of Pennsylvania, on the twenty-seventh day of April, 1808"--P. (v). / Dedicated to Benjamin Smith Barton, M.D., William Barton, and Rev. Samuel Stanhope Smith. With a half-title. Last page blank. Includes bibliographical references. Microform version available in the Readex Early American Imprints series.

Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 124-132).

No description available.

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The greenhouse gas nitrous oxide (N2O) is produced mainly by the microbial processes of nitrification and denitrification. I hypothesized that microbial community structure (composition and abundance) is linked to differences in soil N2O emissions from these two processes. Microbial community composition (type and number of nitrifier and denitrifier genotypes), abundance and N2O emission activity were determined and compared for soils from two landscapes characteristic of the North American prairie pothole region (cultivated vs. uncultivated wetlands). The landscape difference in composition of individual microbial communities was not predictive of soil N2O emissions, indicating that there is redundancy in each microbial community in relation to N2O emission activities. However, community factors influenced the pattern and distribution of N2O emission from the soils of the study site. For example, nitrification was the dominant N2O emitting process for soils of all landforms. However, neither nitrifier amoA abundance nor community composition had predictive relationships with nitrification associated N2O emissions. This lack of relationship may be a consequence of using amoA as the gene target to characterize nitrifiers. For denitrifying bacteria, there was a temporal relationship between community composition and N2O emissions. However, this may be related to the change in water-filled pore space over time. Alternatively, the presence of fungi can be linked directly to N2O emissions from water accumulating landform elements. Under hypoxic conditions, there may be two fungal pathways contributing to N2O release: fungal denitrification via P450nor and fungal heterotrophic nitrification. Results suggest that the relative importance of these two processes is linked to root exudates such as formate. It is the interaction between the seasonal fluctuations of the microbial and environmental factors that determine the level of N2O emissions from soils.

Riparian soils are thought to be potential hotspots for nitrous oxide (N2O) fluxes from incomplete denitrification, with soil moisture cited as a primary controller, however, because there are multiple potential pathways for N2O production in soils, each with their own environmental regulators, the timing and magnitude of N2O fluxes in difficult to predict. Often empirical observations have failed to yield consistent relationships between environmental factors in lab and field scenarios. This thesis characterizes the hydrological controls (soil moisture, water table depth, and precipitation) on N2O fluxes from different positions on the riparian landscape (dry, loamy upland, and wet, organic lowland) in the field during the growing season. Nitrous oxide and carbon dioxide (CO2) fluxes in the field, as well as environmental and climatic variables, were measured in the field. Over the three year study period N2O fluxes were consistently correlated with soil temperature during the growing season, but not with any hydrological factors. However, direct relationship between soil hydrology and N2O fluxes was more evident on an “episodic” time scales. Lab experiments were used to assess the influence of AHC on N2O production under controlled conditions. Experiment 1 employed intact soil cores collected from the upland and lowland positions of the riparian landscape and the cores were subjected to one of two contrasting moisture regimes (wet-dry-wet or dry-wet-dry). Experiment 2 used homogenized soils from the upland and lowland positions on the landscape to create a multi-factorial experiment that simultaneously altered soil moisture and soil substrate concentrations (nitrate, ammonium, organic carbon). The lab results showed that different AHC resulted in differences to the timing and magnitude of N2O fluxes, and that these patterns differed with soil type. Nitrous oxide production was often correlated with soil moisture in the lowland soils regardless of AHC. The results from Experiment 2 suggested that the upland soils were C limited, which resulted in an unpredictable relationship between soil moisture and N2O production during different AHC. The lowland soils were less affected by AHC as they were not N or C limited like the upland soils. It can be concluded from this research that the relationship between soil moisture and N2O fluxes is influenced by AHC through the influence of AHC on soil N and C dynamics. Given the differences in C and N dynamics between soils types, and the influence of AHC on soil C and N, it can be concluded that a derived relationship between soil moisture and N2O fluxes may not be directly transferable between soil types unless C and N are considered.