期刊
ENVIRONMENTAL SCIENCE & TECHNOLOGY
卷 48, 期 16, 页码 9555-9562出版社
AMER CHEMICAL SOC
DOI: 10.1021/es501261s
关键词
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资金
- National Natural Science Foundations [41130525, 41322002, 41271114, 41071135]
- State Key Laboratory of Estuarine and Coastal Research [2010RCDW07]
- NSF [1240798]
- Program for New Century Excellent Talents in University (NCET)
- Marine Scientific Research Project for Public Interest [200905007]
- Direct For Biological Sciences
- Division Of Environmental Biology [1240798] Funding Source: National Science Foundation
Nitrogen (N) pollution in aquatic ecosystems has attracted much attention over the past decades, but the dynamics of this bioreactive element are difficult to measure in aquatic oxygen-transition environments. Nitrogen-transformation experiments often require measurement of N-15-ammonium ((NH4+)-N-15) ratios in small-volume N-15-enriched samples. Published methods to determine N isotope ratios of dissolved ammonium require large samples and/or costly equipment and effort. We present a novel (OX/MIMS) method to determine N isotope ratios for (NH4+)-N-15 in experimental waters previously enriched with N-15 compounds. Dissolved reduced N-15 (dominated by (NH4+)-N-15) is oxidized with hypobromite iodine to nitrogen gas (N-29(2) and/or N-30(2)) and analyzed by membrane inlet mass spectrometry (MIMS) to quantify (NH4+)-N-15 concentrations. The N isotope ratios, obtained by comparing the (NH4+)-N-15 to total ammonium (via autoanalyzer) concentrations, are compared to the ratios of prepared standards. The OX/MIMS method requires only small sample volumes of water (ca. 12 mL) or sediment slurries and is rapid, convenient, accurate, and precise (R-2 = 0.9994, p < 0.0001) over a range of salinities and is N-15/N-14 ratios. It can provide data needed to quantify rates of ammonium regeneration, potential ammonium uptake, and dissimilatory nitrate reduction to ammonium (DNRA). Isotope ratio results agreed closely (R = 0.998, P = 0.001) with those determined independently by isotope ratio mass spectrometry for DNRA measurements or by ammonium isotope retention time shift liquid chromatography for water-column N-cycling experiments. Application of OX/MIMS should simplify experimental approaches and improve understanding of N-cycling rates and fate in a variety of freshwater and marine environments.
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