Labile organic matter favors a low N2O yield during nitrogen removal in estuarine sediments

Abstract

Estuary harbors the active sediment denitrification and nitrous oxide (N₂O) emission, while the knowledge of environmental controls on the denitrification-derived N₂O yield remains underexplored. Here, we quantitatively assess the potential and in situ rates of N₂O production during sediment denitrification in the Pearl River Estuary (PRE), China. Organic matter determines the product stoichiometry and capacity of nitrogen removal. In particular, labile organic matter (LOM) reduces N₂O yield via enhancing the complete coupled nitrification-denitrification. Our results reveal that the chain processes, primary production-LOM settling-sedimentary respiration-coupled nitrification-denitrification, control the sediment denitrification and N₂O production, linking the carbon and nitrogen biogeochemical cycles in the atmosphere-water column-sediment continuum. The PRE sediments serve as nitrogen removal hotspots but with low efficiency (~25 % of riverine input) and strong N₂O release (~66 % of daily sea-air N₂O efflux). These findings contribute to policy makers to develop knowledge-based management actions for achieving sustainable coastal environments and mitigating N₂O emission.

Keywords: Climatic feedback; Denitrification; Labile organic matter; N(2)O production; Sediment.