N₂ production through denitrification and anammox across the continental margin (shelf–slope–rise) of the Ulleung Basin, East Sea

Abstract

Experimental determinations of nitrogen cycling in deep-sea sediments are strongly underrepresented in the databases. To investigate the total N 2 production rates and relative contribution of denitrification and anaerobic ammonium oxidation (anammox) to benthic fixed-N removal processes, we conducted ). The contribution of anammox to the total N 2 production (ra) increased with increasing water depth from the shelf (ca. 17%) to the basin (ca. 56%). The enhanced ra in the center of the UB was associated with an increased availability of nitrite for anammox, which was likely a result of the competitive suppression of denitrification by manganese reduction under MnO 2 -rich conditions. Our results emphasize the importance of anammox as a sink for reactive nitrogen in deep-sea sediments and contribute toward a mechanistic understanding of the factors controlling benthic reactive nitrogen loss in the ocean.

Benthic nitrogen cycling in the North Sea

“…The rates measured, and dominance of canonical denitrification, are very consistent with other data from coastal seas, while much higher rates have been measured in estuarine systems and lower rates beyond the continental shelf (Trimmer and Engström, 2011and references therein, Neubacher et al, 2011, Devol, 2015, Na et al, 2017, Deek et al, 2013. Indeed, these published studies demonstrate that there is quite a strong inverse global relationship between denitrification rates and depth and also that the proportion of anammox to denitrification increases with depth, over depth ranges from 0-5000 m. A number of potential controlling variables for denitrification vary systematically with water depth.…”

“…Measurements on the Irish Sea shelf (4.8 µmol m -2 h -1 ) were also similar (Trimmer and Nicholls, 2009) as were the results of Kitidis et al (2017), although as noted earlier the latter authors found anammox to be dominant. These rates on the N W European shelf are similar to those reported for the Baltic (Deutsch et al, 2010, Asmala et al, 2017 and other shelf seas in the compilation by Trimmer and Engström (2011) and in more recent studies with Na et al (2017) who report values of 9.2 µmol m -2 h -1 in the east China Sea. Thus there is a general consensus for denitrification rates measured using the isotope pairing approach on temperate shelf seas fall in the range of 5-10 µmol m -2 h -1 .…”

Processes and Microorganisms Involved in the Marine Nitrogen Cycle: Knowledge and Gaps

“…The N release from the ocean is mainly caused by denitrification and anammox in a theoretical 71:29 ratio, assuming that anammox consumes all NH 4 + produced from mineralization of C and N in a 106:16 ratio coupled to denitrification (Dalsgaard et al, 2012). The most important factor over marine N loss is O 2 given that denitrification and anammox occur in environments where O 2 is nearly or fully depleted, such as OMZs and sediments, which are responsible for 30-50% and 50-70% of N loss, respectively (Codispoti et al, 2001;Devol, 2015;Na et al, 2018). The interaction of denitrification and anammox with other N processes also affects marine N loss.…”

Denitrification dominates dissimilatory nitrate reduction across global natural ecosystems

“…Second, different soil/sediment incubation methods in experiments may cause some uncertainty in the results. For example, slurry incubation may overestimate the contribution of denitrification to NO 3 − reduction, and intact core incubation may overestimate the contribution of anammox (Na et al., 2018). Third, the majority of experimental sites are distributed in East Asia, Western Europe, and North America.…”