The kinetics of nitrogen utilization in the oceanic mixed layer: nitrate and ammonium interactions at nanomolar concentrations. Limnology and Oceanography

• Main Authors: W. G. Harrison, L. R. Harris, B. D. Irwin
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1996
• Subjects: North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.584.928; http://www.aslo.org/lo/toc/vol_41/issue_1/0016.pdf

The concentration-dependent uptake of nitrate (NO,) and its inhibit ion by ammonium (NH,) were surveyed in surface waters of the North Atlantic Ocean. Low-level NO, determinations combined with conventional tracer methods provided the first comprehensive data set on NO, utlization kinetics at nanomolar concen-trations. Uptake followed saturation kinetics described by the Michaeli s-Menten equation. The half-saturation parameter for uptake (KN) ranged 2-3 orders of magnitude, covarying with ambient NO, concentrations. KN concentrations in oceanic waters averaged-20-30 nM. NH, half-saturation parameters could only be ap-proximated (i.e. KA + A), but observations suggested that KA and K,, were of similar magnitude in oceanic waters. Maximum uptake rates of nitrate, prntN), and ammonium, prncA), covaried, but prncA) almost always exceeded prncN); in oceanic waters, the disparity was an order of magnitude or greater. Most of the variability in A,,( ~ and prncA) could be explained by variations in phytoplankton biomass and temperature. The slope of the uptake vs. concentration relationship, CX, was also investigated but was highly variable and could not be related to any of the oceanographic properties observed; cr, was generally greater than ayN. Kinetics analysis showed that NH4 is preferentially utilized over NO3 over the full spectrum of nitrogen concentrations, nanomolar to micromolar.