The biogeochemistry of marine nitrous oxide

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2011Atmospheric nitrous oxide N2O concentrations have been rising steadily for the past century as a result of human activities. In particular, human perturbation of the nitrogen cycle has increased the N2O production rates of the two major sources of this greenhouse gas, soil and the ocean. Nitrification, and particularly ammonia oxidation, is one of the major processes that produces N2O in the ocean. In this thesis, a series of stable isotopic methods have been used to characterize the biogeochemical controls on N2O production by marine nitrification as well as the natural abundance stable isotopic signatures of N2O produced by marine nitrifiers. This thesis shows that in addition to chemical controls on N2O production rates such as oxygen (O2) and nitrite (NO-2) concentrations, there are also biological controls such as nitrifier cell abundances and coastal phytoplankton blooms that may influence N2O production by ammonia oxidizers as well. Ammonia oxidizers can produce N2O through two separate biochemical mechanisms that have unique isotopic signatures. Using culture- based measurements of these signatures, we conclude that one of these pathways, nitrifier- denitrification, may be a significant source of N2O produced in the South Atlantic Ocean and possibly the global ocean.Funding for this work was provided by NSF/OCE 05-26277, the Andrew W. Mellon Founda- tion Awards for Innovative Research, the Cecil H. and Ida M. Green Technology Innovation Awards, and the W. M. Keck Foundation

An examination of the teaching of motor vehicle technology in colleges in the north east of England

The main purpose behind this work was to try and establish why so many motor vehicle students in the North East of England, having embarked on a course of study, fail to successfully complete it. Briefly, the correlated information indicates:-(a) Students who found their way into the motor industry as apprentices had not, in general, been given sufficient careers advice, either at home or from outside agencies.(b) It was also apparent that many of the students taking part in this work had obtained their apprenticeships by what can only be described as 'chance factors'. There is little evidence to support the view that 'constructive selection' is practised in the motor industry.(c) It was discovered that those students who had been selected for technician courses, primarily because of their superior mathematical ability over their craft counterparts, were far less likely to have had previous employment, and were less likely to leave their college course prematurely.(d) The majority of students taking part showed a willingness to participate in college administration, had very definite opinions on their lecturers and on the way courses should be organised and presented to them, and were far more constructive about these matters than lecturers anticipated,(e) Lecturers, even when given clear definitions of intellectual levels, found it difficult to place specific objectives within these levels, particularly at the higher grades. Nevertheless even accepting a certain amount of confusion concerning the correct intellectual levels of objectives, the results obtained from student evaluation tests were encouraging. The indicants were that specific objectives when used for lesson presentation and/or revision purposes enabled the students to score significantly higher than those students who had been taught and had revised in the traditional way

The operators' cost of producing some field crops in central Missouri

Publication authorized March 20, 1946.Digitized 2007 AES

Cost of producing cotton in southeast Missouri, 1941

Cover title.Includes bibliographical references

The horse and mule outlook

Caption title.Digitized 2006 AES MoU.Includes bibliographical references

Influence of yield on costs and income in agricultural production

Cover title

Reducing the cost of producing dairy and poultry products in Missouri

Caption title.At head of title: A wartime publication.Digitized 2006 AES MoU

The labor required and its distribution in Missouri farm crop production

Publication authorized October 14, 1944.Digitized 2007 AES

The costs of crop production in Missouri, 1921

Cover title.Includes bibliographical references

Biogeochemical controls and isotopic signatures of nitrous oxide production by a marine ammonia-oxidizing bacterium

Nitrous oxide (N2O)[N subscript 2 O] is a trace gas that contributes to the greenhouse effect and stratospheric ozone depletion. The N2O [N subscript 2 O] yield from nitrification (moles N2O-N [N subscript 2 O - N] produced per mole ammonium-N consumed) has been used to estimate marine N2O [N subscript 2 O] production rates from measured nitrification rates and global estimates of oceanic export production. However, the N2O [N subscript 2 O] yield from nitrification is not constant. Previous culture-based measurements indicate that N2O [N subscript 2 O] yield increases as oxygen (O2) [O subscript 2] concentration decreases and as nitrite (NO2−) [NO subscript 2 overscore] concentration increases. Here, we have measured yields of N2O [N subscript 2 O] from cultures of the marine β-proteobacterium [beta-proteobacterium] Nitrosomonas marina C-113a as they grew on low-ammonium (50 μM)[50 mu M] media. These yields, which were typically between 4 × 10−4 [10 superscript -4] and 7 × 10−4 [10 superscript -4] for cultures with cell densities between 2 × 102 [10 super script 2] and 2.1 × 104 [10 superscript 4] cells ml−1 [ml superscript -1], were lower than previous reports for ammonia-oxidizing bacteria. The observed impact of O2 [O subscript 2] concentration on yield was also smaller than previously reported under all conditions except at high starting cell densities (1.5 × 106 cells ml−1) [1.5 x 10 superscript 6 cells ml superscript -1], where 160-fold higher yields were observed at 0.5% O2 [O subscript 2](5.1 μM [mu M] dissolved O2 [O subscript 2]) compared with 20% O2 [O subscript 2] (203 μM [mu M] dissolved O2 O subscript 2]). At lower cell densities (2 × 102 [10 superscript 2] and 2.1 × 104 [10 superscript 4] cells ml−1 [ml superscript -1]), cultures grown under 0.5% O2 [O subscript 2] had yields that were only 1.25- to 1.73-fold higher than cultures grown under 20% O2 [O subscript 2]. Thus, previously reported many-fold increases in N2O [N subscript 2 O] yield with dropping O2 [O subscript 2] could be reproduced only at cell densities that far exceeded those of ammonia oxidizers in the ocean. The presence of excess NO2− [NO subscript 2 overscore] (up to 1 mM) in the growth medium also increased N2O [N subscript 2 O] yields by an average of 70% to 87% depending on O2 [O subscript 2] concentration. We made stable isotopic measurements on N2O [N subscript 2 O] from these cultures to identify the biochemical mechanisms behind variations in N2O [N subscript 2 O] yield. Based on measurements of δ15Nbulk [delta superscript 15 N superscript bulk], site preference (SP = δ15Nα−δ15Nβ [delta superscript 15 N superscript alpha - delta superscript 15 N superscript beta]), and δ18O [delta superscript 18 O] of N2O [N subscript 2 O] (δ18O-N2O [delta superscript 18 O - N subscript 2 O]), we estimate that nitrifier-denitrification produced between 11% and 26% of N2O [N subscript 2 O] from cultures grown under 20% O2 [O subscript 2] and 43% to 87% under 0.5% O2 [O subscript 2]. We also demonstrate that a positive correlation between SP and δ18O-N2O [delta superscript 18 O - N subscript 2 O] is expected when nitrifying bacteria produce N2O [N subscript 2 O]. A positive relationship between SP and δ18O-N2O [delta superscript 18 O - N subscript 2 O] has been observed in environmental N2O [N subscript 2 O] datasets, but until now, explanations for the observation invoked only denitrification. Such interpretations may overestimate the role of heterotrophic denitrification and underestimate the role of ammonia oxidation in environmental N2O [N subscript 2 O] production