Aquatic Sciences Meeting, Albuquerque 2001

SS08 Processes at the Benthic Interface (Environmental Connections)

Date: Monday, February 12, 2001, Time: 2:30:00 PM

Location: Ruidoso/Pecos

An, S, , Unversity of Texas Marine Science Institute, Port Aransas, USA, soonmo@utmsi.utexas.edu

Gardner, W, S, Unversity of Texas Marine Science Institute, Port Aransas, USA, gardner@utmsi.utexas.edu

Kana, T, , The University of Maryland, Horn Point Laboratory, Cambridge, USA, kana@hpl.umces.edu

DENITRIFICATION AND NITROGEN FIXATION MEASUREMENT USING ISOTOPE PAIRING WITH MEMBRANE INLET MASS SPECTROMETER (MIMS) ANALYSIS.

A method was developed to estimate denitrification and nitrogen fixation simultaneously in coastal sediments. An isotope pairing technique was applied to dissolved gas measurements with a membrane inlet mass spectrometer (MIMS). The relative fluxes of three N2 gas species (28N2, 29N2 and 30N2) were monitored during incubation experiments after addition of 15NO3-. Formulas were developed to estimate the production (denitrification) and consumption (N2 fixation) of N2 gas from the fluxes of the different isotopic forms of N2. Proportions of the three isotopic forms produced from 15NO3- and 14NO3- agreed with expectations in a sediment slurry incubation experiment designed to optimize conditions for denitrification. Denitrification and nitrogen fixation rates were estimated in April 2000 on sediments from a Texas seagrass bed (Laguna Madre). Denitrification rates (AVG=20 micro-g atom N m-2h-1) were lower than nitrogen fixation rates (AVG=60 micro-g atom N m-2h-1). The developed method benefits from simple and accurate dissolved gas measurement by the MIMS system. By adding the N2 isotope capability, it was possible to do isotope pairing experiments with the MIMS system.

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Aquatic Sciences Meeting, Albuquerque 2001

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