MEPS 240:1-9 (2002)  -  doi:10.3354/meps240001

ABSTRACT: This paper examines the effect of oxygen on nitrous oxide (N₂O) concentrations in estuarine waters. N₂O has been measured year-round in the Schelde estuary, a high-nitrogen, low-oxygen macrotidal system. N₂O concentrations were above atmospheric equilibrium levels indicating that this estuary represents a source to the atmosphere. The distribution of N₂O showed consistent and systematic relationships with distribution patterns of ammonium, oxygen, nitrite and nitrification activities. A controlled laboratory experiment with a natural bacterial community from the Schelde estuary revealed maximum N₂O production to occur at oxygen concentrations of about 5 µM. This production was inhibited by acetylene, a nitrification inhibitor. Maximum N₂O concentration in the field occurred at oxygen concentrations below 35 µM. The difference in the oxygen concentration that results in maximum N₂O may have arisen because low-oxygen environments present in the estuary were destroyed by stirring in our laboratory experiment. It appears that low oxygen concentrations in estuarine water trigger enhanced N₂O production if ammonium is present in sufficient amounts. This conclusion is further illustrated by data from the Thames, Loire and Gironde estuaries.

KEY WORDS: Nitrous oxide · Nitrification · Oxygen · Ammonium · Estuary · Scheldt · Thames · Loire · Gironde