Nathaniel E. Ostrom

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There is much interest in biogeochemical processes that occur at the interface between soils and streams since, at the scale of landscapes, these habitats may function as control points for fluxes of nitrogen (N) and other nutrients from terrestrial to aquatic ecosystems. Here we examine whether a thermodynamic perspective can enhance our mechanistic and(More)
Spirochetes from termite hindguts and freshwater sediments possessed homologs of a nitrogenase gene (nifH) and exhibited nitrogenase activity, a previously unrecognized metabolic capability in spirochetes. Fixation of 15-dinitrogen was demonstrated with termite gut Treponema ZAS-9 and free-living Spirochaeta aurantia. Homologs of nifH were also present in(More)
The intramolecular distribution of nitrogen isotopes in N2O is an emerging tool for defining the relative importance of microbial sources of this greenhouse gas. The application of intramolecular isotopic distributions to evaluate the origins of N2O, however, requires a foundation in laboratory experiments in which individual production pathways can be(More)
The relative importance of individual microbial pathways in nitrous oxide (N(2)O) production is not well known. The intramolecular distribution of (15)N in N(2)O provides a basis for distinguishing biological pathways. Concentrated cell suspensions of Methylococcus capsulatus Bath and Nitrosomonas europaea were used to investigate the site preference of(More)
Bacteria and functional genes associated with biphenyl (BP) degradation in the root zone of an Austrian pine (Pinus nigra L.) growing naturally in polychlorinated-BP (PCB)-contaminated soil were identified using stable isotope probing (SIP) integrated with comprehensive functional gene analyses. SIP revealed 75 different genera that derived carbon from(More)
The stable nitrogen isotopic composition of nitrate, concentrations of inorganic nitrogen and phosphorus, dissolved oxygen and nitrification rates were determined at six stations ranging from the oligotrophic North Pacific Subtropical Gyre (NPSG) to the more productive Eastern Tropical North Pacific (ETNP). Nitrification rates increased along the transect(More)
[1] Although the oceans are a significant source of the greenhouse gas nitrous oxide (N2O) to the atmosphere, the magnitude and characteristics of this source are poorly constrained. We present here stable isotope and isotopomer (intramolecular distribution of N within the linear NNO molecule) results for N2O and oxygen stable isotopic data for dissolved O2(More)
In this study, we compare stable isotopic compositions of di-oxygen (O2) and nitrous oxide (N2O) in two depth pro®les at the well-characterized deep water station ALOHA (A Long-term Oligotrophic Habitat Assessment) in the subtropical North Paci®c gyre to attain an understanding of the mechanisms of N2O production. The dO of O2 varied from values indicative(More)
[1] Site preference (SP), the difference in dN between the central and outer nitrogen atoms in N2O, is a powerful approach for apportioning fluxes of N2O from soils to nitrification and denitrification (Sutka et al., 2006). A critical aspect of the use of SP data to apportion sources of N2O to nitrification and denitrification is the need to evaluate data(More)
The natural removal of NO3 by denitrification within riparian zones of streams and rivers is an area of considerable interest owing to its potential to minimize the impacts of excess anthropogenic loadings. In this study we utilize natural variations in stable N isotopic compositions of NO3 and NH4 within a transect of shallow wells extending 4 m inland(More)