Metabolic specialization of denitrifiers in permeable sediments controls N₂O emissions

Abstract

Coastal oceans receive large amounts of anthropogenic fixed nitrogen (N), most of which is denitrified in the sediment before reaching the open ocean. Sandy sediments, which are common in coastal regions, seem to play an important role in catalysing this N-loss. Permeable sediments are characterized by advective porewater transport, which supplies high fluxes of organic matter into the sediment, but also leads to fluctuations in oxygen and nitrate concentrations. Little is known about how the denitrifying communities in these sediments are adapted to such fluctuations. Our combined results indicate that denitrification in eutrophied sandy sediments from the world's largest tidal flat system, the Wadden Sea, is carried out by different groups of microorganisms. This segregation leads to the formation of N O which is advectively transported to the overlying waters and thereby emitted to the atmosphere. At the same time, the production of N O within the sediment supports a subset of Flavobacteriia which appear to be specialized on N O reduction. If the mechanisms shown here are active in other coastal zones, then denitrification in eutrophied sandy sediments may substantially contribute to current marine N O emissions.

Seasonality of Organic Matter Degradation Regulates Nutrient and Metal Net Fluxes in a High Energy Sandy Beach

“…Nitrate reduction in subterranean estuaries can be driven by inputs of NO 3 − from fresh groundwater and inputs of marine organic matter (Couturier et al, 2017;Kim et al, 2017) as well as by seawater supplied NO 3 − . In combination with coupled nitrification-denitrification, the reduction of NO 3 − to nitrogen gas through denitrification can lead to substantial N-loss as N 2 and N 2 O, which has been observed for permeable intertidal and subtidal sediments (Marchant et al, 2016;Marchant et al, 2018). The net removal of dissolved inorganic nitrogen (DIN) in beaches may therefore affect nutrient budgets in coastal regions where inputs of NO 3 − are high due to anthropogenic activities (Johannsen et al, 2008).…”

Habitat diversity and type govern potential nitrogen loss by denitrification in coastal sediments and differences in ecosystem-level diversities of disparate N2O reducing communities

“… 2010 ; Jones and Hallin 2010 ; Mosier and Francis 2010 ; Marchant et al . 2018 ). Regarding the potential for N 2 O reduction, clade II nosZ genes were more abundant than those of clade I, with a nosZ clade I to clade II ratio of 0.77 (SD ± 0.41; Fig.…”

“… 2016 ; Marchant et al . 2018 ). However, differences among sediment types and how these microbial communities may be affected by losses in habitat diversity is not known, despite the importance of these shallow-water coastal environments as nutrient filters.…”

Application of the isotope pairing technique in sediments: Use, challenges, and new directions

“…Studies investigating N cycling in intertidal sandy sediments have used flow‐through sediment columns (Rao et al ; Evrard et al ), percolation techniques (Gao et al ; Marchant et al , ), experimental chamber simulations (Cook et al ), stirred reactors (Cook et al ), push‐pull methods (Erler et al ), flume experiments (Kessler et al ), in situ advective chambers (Eyre et al ), and various modeling techniques (Cook et al ; Kessler et al , ; Neumann et al ) to account for advective solute exchange. These studies have demonstrated the great importance of this sediment type for benthic N turnover and loss through N 2 (Eyre et al , ; Gao et al ; Marchant et al ) and/or N 2 O production (Marchant et al ). In advection‐dominated environments, direct comparisons of diffusive and advective techniques demonstrated that advective flow regimes resulted in N 2 production 1–2 orders of magnitude greater than under diffusive conditions (e.g., Gihring et al ; Gao et al ).…”