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Stable nitrogen isotopes as a tool f...

Sutka, Robin Leslie.

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Stable nitrogen isotopes as a tool for understanding nitrogen cycling processes and mechanisms responsible for nitrous oxide production.

紀錄類型:	書目-語言資料,印刷品 : Monograph/item
正題名/作者:	Stable nitrogen isotopes as a tool for understanding nitrogen cycling processes and mechanisms responsible for nitrous oxide production./
作者:	Sutka, Robin Leslie.
面頁冊數:	68 p.
附註:	Adviser: Peggy Ostrom.
Contained By:	Dissertation Abstracts International63-09B.
標題:	Biogeochemistry. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3064317
ISBN:	0493832831

Stable nitrogen isotopes as a tool for understanding nitrogen cycling processes and mechanisms responsible for nitrous oxide production.
Sutka, Robin Leslie.

Stable nitrogen isotopes as a tool for understanding nitrogen cycling processes and mechanisms responsible for nitrous oxide production. - 68 p.

Adviser: Peggy Ostrom.

Thesis (Ph.D.)--Michigan State University, 2002.

The stable nitrogen isotopic composition of dissolved nitrate was determined at six stations ranging from the oligotrophic North Pacific Subtropical Gyre (NPSG) to the eutrophic Eastern Tropical North Pacific (ETNP). Dissolved inorganic nitrogen, oxygen and phosphate concentrations were determined in water column samples at all six stations. In productive, oxic waters nitrate isotopically enriched in <super>15</super>N (maximum δ<super>15</super>N-NO 3<super>−</super> value of 12.5&permil;) was most likely the result of assimilatory nitrate reduction. In contrast, high δ<super>15</super>N-NO 3<super>−</super> values (maximum of 12.3&permil;) associated with high nitrate deficits and anoxic conditions, supported the interpretation of isotopic fractionation due to denitrification. A one-dimensional vertical advection and diffusion model was used to estimate the fractionation factor for denitrification at two stations in the ETNP. A comparison of modeled to observed δ<super>15</super>N-NO3<super>−</super> provided estimates of the isotopic enrichment factor (ϵ) of 30 at station 4 and 30 to 35 at station 5. Isotopically light nitrate (1.1 and 3.2&permil;) was observed in the upper 200 m of the water column at stations in the ETNP. Tracer studies of <super>15</super>NH4 and biogeochemical indicators of nitrogen fixation, such as N/P ratios, δ<super>15</super>N-POM and <italic> Trichodesmium</italic> abundance, supported the interpretation of nitrification as the most plausible explanation for low δ<super>15</super>N-NO 3<super>−</super> values observed in upper water column samples. Nitrification rates increased across the transect from a maximum rate of 1 nmol 1<super>−1</super> d<super>−1</super> at station 1 and 23.7 nmol 1<super>−1</super> d<super>−1</super> at station 6.

ISBN: 0493832831Subjects--Topical Terms:

545717
Biogeochemistry.

Stable nitrogen isotopes as a tool for understanding nitrogen cycling processes and mechanisms responsible for nitrous oxide production.
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100 1 $a Sutka, Robin Leslie. $3 1252885
245 1 0 $a Stable nitrogen isotopes as a tool for understanding nitrogen cycling processes and mechanisms responsible for nitrous oxide production.
300 $a 68 p.
500 $a Adviser: Peggy Ostrom.
500 $a Source: Dissertation Abstracts International, Volume: 63-09, Section: B, page: 4087.
502 $a Thesis (Ph.D.)--Michigan State University, 2002.
520 $a The stable nitrogen isotopic composition of dissolved nitrate was determined at six stations ranging from the oligotrophic North Pacific Subtropical Gyre (NPSG) to the eutrophic Eastern Tropical North Pacific (ETNP). Dissolved inorganic nitrogen, oxygen and phosphate concentrations were determined in water column samples at all six stations. In productive, oxic waters nitrate isotopically enriched in <super>15</super>N (maximum δ<super>15</super>N-NO 3<super>−</super> value of 12.5&permil;) was most likely the result of assimilatory nitrate reduction. In contrast, high δ<super>15</super>N-NO 3<super>−</super> values (maximum of 12.3&permil;) associated with high nitrate deficits and anoxic conditions, supported the interpretation of isotopic fractionation due to denitrification. A one-dimensional vertical advection and diffusion model was used to estimate the fractionation factor for denitrification at two stations in the ETNP. A comparison of modeled to observed δ<super>15</super>N-NO3<super>−</super> provided estimates of the isotopic enrichment factor (ϵ) of 30 at station 4 and 30 to 35 at station 5. Isotopically light nitrate (1.1 and 3.2&permil;) was observed in the upper 200 m of the water column at stations in the ETNP. Tracer studies of <super>15</super>NH4 and biogeochemical indicators of nitrogen fixation, such as N/P ratios, δ<super>15</super>N-POM and <italic> Trichodesmium</italic> abundance, supported the interpretation of nitrification as the most plausible explanation for low δ<super>15</super>N-NO 3<super>−</super> values observed in upper water column samples. Nitrification rates increased across the transect from a maximum rate of 1 nmol 1<super>−1</super> d<super>−1</super> at station 1 and 23.7 nmol 1<super>−1</super> d<super>−1</super> at station 6.
520 $a The relative importance of individual microbial pathways to nitrous oxide production is not well known. The intramolecular distribution of <super>15 </super>N in nitrous oxide provides a basis for distinguishing biological pathways. Concentrated cell suspensions of <italic>M. capsulatus</italic> Bath and <italic>N. europaea</italic> were used to investigate the site preference of nitrous oxide by microbial processes during nitrification. The average site preference of nitrous oxide formed by hydroxylamine oxidation by <italic> M. capsulatus</italic> Bath (5.5 +/− 3.1&permil;) and <italic>N. europaea </italic> (−1.4 +/− 1.7&permil;) and nitrite reduction by <italic> N. europaea</italic> (−7.7 +/− 3.1&permil;) differed significantly (ANOVA, f(2,35) = 247.9, p = 0). These results demonstrate that the mechanisms for hydroxylamine oxidation are distinct in <italic>M. capsulatus </italic> Bath and <italic>N. europaea</italic>. The average δ<super> 18</super>O-N2O values of nitrous oxide formed during hydroxylamine oxidation by <italic>M. capsulatus</italic> Bath (53.1 +/− 2.9&permil;) and <italic>N. europaea</italic> (−23.4 +/− 7.2) and nitrite reduction by <italic>N. europaea</italic> (4.6 +/− 1.4) were also significantly different (ANOVA, f(2,35) = 279.98, p = 0) and suggests although the nitrogen isotope value of the hydroxylamine was similar, the Δ<super> 15</super>N associated with hydroxylamine oxidation by <italic>M. capsulatus </italic> Bath and <italic>N. europaea</italic> (−2.3 and 26.0&permil; for <italic>M. capsulatus</italic> Bath and <italic>N. europaea </italic> respectively) provided evidence that differences in isotopic fractionation were associated with two mechanisms. The site preferences in this study are the first measured values for isolated microbial processes. The differences in site preference are significant and indicate that isotopomers provide a basis for apportioning biological processes of nitrous oxide.
590 $a School code: 0128.
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710 2 0 $a Michigan State University. $3 676168
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791 $a Ph.D.
792 $a 2002
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