106 research outputs found
Biogeochemical controls and isotopic signatures of nitrous oxide production by a marine ammonia-oxidizing bacterium
No full textNitrous 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
The biogeochemistry of marine nitrous oxide
No full textSubmitted 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
N2O production in the eastern South Atlantic: analysis of N2O stable isotopic and concentration data
No full textThe stable isotopic composition of dissolved nitrous oxide (N2O) is a tracer for the production, transport, and consumption of this greenhouse gas in the ocean. Here we present dissolved N2O concentration and isotope data from the South Atlantic Ocean, spanning from the western side of the mid-Atlantic Ridge to the upwelling zone off the southern African coast. In the eastern South Atlantic, shallow N2O production by nitrifier denitrification contributed a flux of isotopically depleted N2O to the atmosphere. Along the African coast, N2O fluxes to the atmosphere of up to 46 µmol/m2/d were calculated using satellite-derived QuikSCAT wind speed data, while fluxes at the offshore stations averaged 0.04 µmol/m2/d. Comparison of the isotopic composition of the deeper N2O in the South Atlantic (800 m to 1000 m) to measurements made in other regions suggests that water advected from one or more of the major oxygen deficient zones contributed N2O to the mesopelagic South Atlantic via the Southern Ocean. This deeper N2O was isotopically and isotopomerically enriched (δ15Nbulk − N2O = 8.7 ± 0.1‰, δ18O − N2O = 46.5 ± 0.2‰, and Site Preference = 18.7 ± 0.6‰) relative to the shallow N2O source, indicating that N2O consumption by denitrification influenced its isotopic composition. The N2O concentration maximum was observed between 200 m and 400 m and reached 49 nM near the Angolan coast. The depths of the N2O concentration maximum coincided with those of sedimentary particle resuspension along the coast. The isotopic composition of this N2O (δ15Nbulk − N2O = 5.8 ± 0.1‰, δ18O − N2O = 39.7 ± 0.1‰, and Site Preference = 9.8 ± 1.0‰) was consistent with production by diffusion-limited nitrate (NO3−) reduction to nitrite (NO2−), followed by NO2− reduction to N2O by denitrification and/or nitrifier denitrification, with additional N2O production by NH2OH decomposition during NH3 oxidation. The sediment surface, benthic boundary layer, or particles resuspended from the sediments are likely to have provided the physical and chemical conditions necessary to produce this N2O
Microbial and abiotic nitrous oxide cycling in the water column of meromictic, iron-rich Lake La Cruz, Spain, 2015-2017
No full textWe investigated the microbial and abiotic N2O cycle in the water column of iron-rich, meromictic Lake La Cruz, Spain, during two sampling campaigns in March 2015 and March 2017. At the deepest point of the lake, we used a profiling in situ analyzer equipped with several probes and optodes to detect physicochemical parameters. In addition, we collected water column samples via an in situ pump in order to analyze concentrations of N, S, and Fe species as well as isotope characteristics of several N species. In 2017, we used a Niskin bottle to take water samples from 8.0 and 14.5 m depth for two types of incubation experiments. In the first set of experiments, we added 15N-labeled substrates, and in some incubations Fe2+, to filtered and unfiltered lake water, and analyzed the produced N2O, N2, and NH4+. In the other experiment, we determined the N and O isotope effects of NO2- and N2O during chemodenitrification (reaction of NO2- and Fe2+) in anoxic and sterile lake water from 14.5 m depth
Incubation experiment characterizing chemodenitrification in the water column of Lake La Cruz, Spain
No full textProfiles of N, Fe, and S compounds - concentration and isotopes in the water column of Lake La Cruz, Spain
No full text
Demonstration of the equivalence of rotations applied to transform the 3D LDV (extrinsic) reference frame to the stapes (intrinsic) reference frame.
No full textAll panels show the extrinsic (x-y-z) reference frame in black, superposed over a photograph of the stapes and surroundings taken by the camera through the dichroic mirror on the 3D LDV and rotated slightly to show the z axis more clearly. The origin is at the center of the stapes footplate. (A-D) Rotations in TB20 in the order they were measured; (E-H) Rotations in the order used by the Spatial Math Toolbox. (A) Extrinsic reference frame; (B) rotation of +20° about the z axis (blue arrow) to align the y axis (green) to the projection of the stapes piston direction in the x-y plane–the rotated x and y axes are shown in red and green respectively; (C) additional rotation of +40° about the (new) x axis (red arrow) = elevation from the x-y plane–the rotated z axis is shown in blue; (D) additional rotation of –150° about the (new) y axis (green arrow) to arrive at the Maj-pist-min intrinsic reference frame (red-green-blue). (E) The extrinsic coordinate system as in (A); (F) rotation of –139° about the z axis (blue arrow); (G) additional rotation of –22° about the (new) y axis (green arrow); (H) additional rotation of +135° about the (new) x axis (red arrow). Panels (D) and (H) are identical, which shows that the two rotation sequences are equivalent. (TIF)</p
Carta sobre el progreso de la conversión indígena en la Misión del Santísimo Rosario de Viñadaco, 1775 septiembre 10
No full textCarta de Fray Manuel Pérez y Fray Francisco Galisteo a Fray Vicente Mora reportando sobre el progreso de la conversión en la Misión del Santísimo Rosario de Viñadaco. En el informe, los dominicos brindan un breve desglose del número de personas que han "convertido". Luego dan un relato detallado de una confrontación que tuvo el capitán español que los acompaña con hombres indígenas hostiles, uno de ellos llamado Macapa. Los frailes indican que la enfermedad aquejaba a la comunidad indígena, proporcionando algunas cifras de la población enferma. El relato también describe otras excursiones que realizaron los frailes a comunidades cercanas, expresando la necesidad de más soldados dada la hostilidad que experimentaban. —— Letter from Fray Manuel Pérez and Fray Francisco Galisteo to Fray Vicente Mora reporting on their progress indoctrinating Indigenous people at Mission of Santísimo Rosario de Viñadaco. In the report, the Dominicans provide a brief breakdown of the number of people they have "converted". They then provide a detailed account of a confrontation the accompanying Spanish captain had with hostile Indigenous men, one of them named Macapa. The friars indicate that illness was afflicting the unfriendly Indigenous community, providing some population numbers on the ill. The account also describes other excursions the friars made to nearby communities, expressing the need for more soldiers to accompany them given the hostility they encounter. 2 f. (4 p.
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