Factors controlling nitrous oxide at the microbial community and estuarine scale

Abstract

This paper examines the effect of oxygen on nitrous oxide (N 2 O) concentrations in estuarine waters. N 2 O has been measured year-round in the Schelde estuary, a high-nitrogen, lowoxygen macrotidal system. N 2 O concentrations were above atmospheric equilibrium levels indicating that this estuary represents a source to the atmosphere. The distribution of N 2 O 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 N 2 O production to occur at oxygen concentrations of about 5 µM. This production was inhibited by acetylene, a nitrification inhibitor. Maximum N 2 O concentration in the field occurred at oxygen concentrations below 35 µM. The difference in the oxygen concentration that results in maximum N 2 O 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 N 2 O production if ammonium is present in sufficient amounts. This conclusion is further illustrated by data from the Thames, Loire and Gironde estuaries.

N2O cycling at the core of the oxygen minimum zone off northern Chile

“…Our results show that below suboxic conditions, this process takes place -as deduced from global models (Nevison et al 2003) or through direct measurements on waters of the Indian Shelf (Naqvi et al 2000), the Baltic Sea (Brettar & Rheinheimer 1992), suboxic estuaries (De Bie et al 2002), and marine bacteria cultures (Goreau et al 1980, Bonin et al 1989, De Bie et al 2002where the N 2 O produced from NH 4 + oxidation increased within microenvironments having low O 2 and NH 4 + availability (Avrahami et al 2002). In addition to this, potential nitrification rates (0.091 to 0.62 µM d -1 ) have been measurable in the OMZ core off Iquique (V. Molina et al unpubl.…”

Natural and human-induced hypoxia and consequences for coastal areas: synthesis and future development

“…CO 2 , CH 4 , and N 2 O) accumulated in hypoxic waters beneath the stratified surface layer can be released into the atmosphere, potentially having a considerable feedback to climate change. It has been suggested that coastal hypoxic areas are important contributors to the atmospheric inventory of long-lived greenhouse gases (Naqvi et al, 2000De Bie et al, 2002;Zhang et al, 2008). Coastal hypoxia can also influence the oceanic inventory of dissolved oxygen, nutrients and other greenhouse gases through exchange with open ocean waters and down-welling.…”

“…In the few coastal hypoxic systems that are mostly anthropogenically formed and have been sampled for N 2 O, substantial enhancement of N 2 O concentration has been reported. Coastal hypoxia due to eutrophication are hot spots for N 2 O release not only because of low oxygen conditions, but also because of high nitrogen loadings and fluxes (De Bie et al, 2002). For instance, off the mouth of Changjiang in the East China Sea, concentrations of N 2 O in the hypoxic layer (i.e.…”

Distributions and sea-to-air fluxes of nitrous oxide in the South China Sea and the West Philippines Sea

“…In the water column with low oxygen concentrations and in sediments or inside suspended particles, nitrification and denitrification can occur simultaneously and are often closely coupled (Seitzinger, 1988;Ward et al, 1989;Capone, 1991;Middelburg et al, 1996;Barnes and Owens, 1998;Naqvi et al, 1998;Robinson et al, 1998;Usui et al, 2001;Nevison et al, 2003;Codispoti et al, 2005;Bange, 2008). The yield of N 2 O from both processes is highly dependent on the concentration of dissolved oxygen (Goreau et al, 1980;de Bie et al, 2002;Naqvi et al, 2010).…”