A method for the determination of nitrification rates in oligotrophic marine seawater by gas chromatography/mass spectrometry |
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| Institution: | 1. School of Biological Sciences, University of Hong Kong, Pok Fu Lam, Hong Kong, PR China;2. Swire Institute of Marine Science, University of Hong Kong, Cape D''Aguilar, Hong Kong, PR China;3. Department of Earth Sciences, University of Hong Kong, Pok Fu Lam, Hong Kong, PR China;4. State Key Laboratory of Marine Environmental Science, Xiamen University, PR China;1. GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1–3, 24148 Kiel, Germany;2. NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, Texel, The Netherlands;1. University of Helsinki, Department of Environmental Sciences, Division of Aquatic Sciences, P.O. Box 65, 00014 University of Helsinki, Finland;2. Princeton University, Department of Geosciences, 217 Guyot Hall, Princeton, NJ 08544, United States;3. Leibniz Institute for Baltic Sea Research Warnemünde, Department of Biological Oceanography, Seestrasse 15, D-18119 Rostock, Federal Republic of Germany;1. Key Laboratory of Marine Ecosystem and Biogeochemistry, Second Institute of Oceanography, State Oceanic Administration, NO.36 Baochu Bei Road, Hangzhou 310012, China;2. State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration, NO.36 Baochu Bei Road, Hangzhou 310012, China |
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| Abstract: | An isotope dilution method has been developed to determine by gas chromatography/mass spectrometry (GC/MS) the rates of ammonium and nitrite oxidation in severely oligotrophic marine waters. The method is based on the formation of sudan-1 from nitrite, or from nitrate following reduction to nitrite. Samples were collected by solid phase extraction and purified by high performance liquid chromatography (HPLC). A deuterated sudan-1 internal standard was synthesized, purified by HPLC and used for quantitative analysis. Concentrations of NO2? and NO3? were generally < 2 nmol/kg and < 5 nmol/kg respectively, typical of oligotrophic surface waters, and turnover times for the inorganic N pools ranged from < 1 day to > 10 days. Significant rates of nitrification were measured in the surface oligotrophic ocean, with rates of ammonium and nitrite oxidation generally within the range of 10–500 pmol/kg/h. Consequently, a significant proportion of daily NO3? assimilation by marine phytoplankton is regenerated, and not new. In a case study of the oligotrophic gyre of the North Atlantic, the influence of NH4+ regeneration and nitrification on f-ratio values suggests that in the oligotrophic ocean, f-ratio values may be significantly, and sometimes grossly, overestimated. |
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