Sites of Marine Denitrification

Various methods have been used to estimate water-column denitrification rates including stoichiometric relationships, measurements of the enzymatic activity of the electron transport system (ETS), and N03 incubation experiments. In combination with residence times or mass transport calculations these measurements yield areal denitrification rates. 

Three primary methods have been used to calculate expected NOj and aU are based on Redfieldian stoichiometry. 

The first quantitative estimates of denitrification in the eastern tropical North Pacific were made by Codispoti and Richards (1976). Codispoti and Richards used apparent oxygen utilization, AOU, and phosphate data to stoichiometricaUy extrapolate back to the nitrate concentration present when a given water mass was previously at the surface. In this way they were able to develop a relationship between pNOj and sigma-f for waters of the ETNP-ODZ, from which they calculated nitrate deficit as outlined in Eq. (6.4). 

A second method used to calculate nitrate deficit takes advantage of the semiconservative water-mass tracer NO (Broecker, 1974). StoichiometricaUy, every mole of O2 respired wiU remineralize approximately 1/9 of a mole of NOJ so that NO, defined as 

one can then calculate the nitrate deficit from Eq. (6.4). This method has been used primarily to estimate denitrification rates in the Arabian Sea (HoweU et ah, 1997 Mantoura et ah, 1993 Naqvi, 1987). 

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