Hydrodynamics Control Nitrous Oxide Production in Eutrophic Coastal Permeable Sediments

Abstract

Permeable sediments, which make up almost half of the continental shelf worldwide, are potential sources of the important greenhouse gas N₂O from coastal regions. Yet, the extent to which interactions between these sediments and anthropogenic pollution produce N₂O is still unknown. Here we use laboratory experiments and modeling to explore the factors controlling N₂O production at a eutrophic site in a temperate shallow marine embayment (Port Phillip Bay, Australia). Our results show that denitrification is the main source of N₂O production within permeable sediments, but the extent to which N₂O is actually released is determined by the rate of seawater exchange with the sediment bed (which governs solute residence time within the bed). In wave-dominated coastal areas, shallower water with more intense waves (wave height > 1 m) release the most N₂O, with up to 0.5% of dissolved inorganic nitrogen pumped into biologically active eutrophic sediment being released as N₂O. Our results suggest rates of N₂O production in coastal permeable sediments are generally low compared to other environments.