Nitrous oxide production and consumption in a eutrophic coastal embayment

Abstract

Nitrous oxide (N 2O) production and consumption rates, dissolved oxygen, ammonium, and nitrate were measured in the water column of the Bedford Basin, Nova Scotia, Canada, from June 2001 to December 2002. Ammonium oxidation rates were determined during the latter half of the study period. Nitrification was the predominant source of N 2O with production rates ranging from undetectable to 1.7 nmol N 2O l −1 day −1. N 2O production from denitrification was detected on two occasions coinciding with oxygen minima and was in the range 20−40 pmol N 2O l −1 day −1. N 2O consumption (−74 pmol N 2O l −1 day −1) was seen only at the lowest recorded oxygen level of ∼2.5 μmol l −1. The yield of N 2O from ammonium oxidation (100 mol N 2O/mol NH 4 +) varied from 0.01% to 0.11% and showed a negative nonlinear relationship with dissolved oxygen in the range 27−290 μmol O 2 l -1. Nitrification and N 2O production rates did not appear to be related to temperature or ammonium concentration but were suppressed during periods of mixing.