Evidence of Nitrogen Loss from Anaerobic Ammonium Oxidation Coupled with Ferric Iron Reduction in an Intertidal Wetland

Abstract

Anaerobic ammonium oxidation coupled with nitrite reduction is an important microbial pathway of nitrogen removal in intertidal wetlands. However, little is known about the role of anaerobic ammonium oxidation coupled with ferric iron reduction (termed Feammox) in intertidal nitrogen cycling. In this study, sediment slurry incubation experiments were combined with an isotope-tracing technique to examine the dynamics of Feammox and its association with tidal fluctuations in the intertidal wetland of the Yangtze Estuary. Feammox was detected in the intertidal wetland sediments, with potential rates of 0.24-0.36 mg N kg(-1) d(-1). The Feammox rates in the sediments were generally higher during spring tides than during neap tides. The tidal fluctuations affected the growth of iron-reducing bacteria and reduction of ferric iron, which mediated Feammox activity and the associated nitrogen loss from intertidal wetlands to the atmosphere. An estimated loss of 11.5-18 t N km(-2) year(-1) was linked to Feammox, accounting for approximately 3.1-4.9% of the total external inorganic nitrogen transported into the Yangtze Estuary wetland each year. Overall, the co-occurrence of ferric iron reduction and ammonium oxidation suggests that Feammox can act as an ammonium removal mechanism in intertidal wetlands.

Electron Shuttles Enhance Anaerobic Ammonium Oxidation Coupled to Iron(III) Reduction

“…Iron(III)-reducing bacteria are reported to affect Feammox by controlling Fe(III) reduction in anaerobic environments. 6 The addition of AQDS and biochar significantly stimulated the growth of bacteria and archaea, especially the iron-reducing bacteria (Figure 4 and Tables S8 and S11). It is well-documented that addition of extracellular quinone is a strategy for stimulating Fe(III) reduction in many environments.…”

DNRA in intertidal sediments of the Yangtze Estuary

“…Thus, the importance of DNRA may still be improved by salinity in the study area [ Seo et al ., ; Hou et al ., ; Deng et al ., ]. Fe oxides are intimately related to nitrate reduction processes, as Fe 2+ oxidation may be coupled with denitrification and DNRA [ Yin et al ., ; Deng et al ., ], and Fe 3+ reduction can be coupled to anammox [ Li et al ., ]. Fe 2+ can be used by chemolithoautotrophic microbes to conduct DNRA via being oxidized by nitrite (equation ).…”

Piecewise Structural Equation Model (SEM) Disentangles the Environmental Conditions Favoring Diatom Diazotroph Associations (DDAs) in the Western Tropical North Atlantic (WTNA)

“…Earlier studies in the WTNA have reported the influence of the AR and aeolian dust deposition on a variety of parameters related to the N cycle, e.g., DIN (Ryther et al, 1967; DeMaster and Pope, 1996; DeMaster and Aller, 2001), trace metal concentrations (Boyle et al, 1977; Chen and Siefert, 2004; Kaufman et al, 2005; Bergquist and Boyle, 2006), the presence and distribution of N 2 fixing populations, including symbiotic diatoms (Villareal, 1994; Carpenter et al, 1999; Foster et al, 2007; Subramaniam et al, 2008; Goebel et al, 2010; Turk-Kubo et al, 2012; Goes et al, 2014; Hilton et al, 2015; Zelinski et al, 2016), carbon export (Cooley et al, 2007; Subramaniam et al, 2008; Yeung et al, 2012), and N 2 and C fixation (Carpenter et al, 1999; Montoya et al, 2002; Sohm et al, 2011; Fernández-Castro et al, 2015). Given the new N supplied by symbiotic diazotrophy in the WTNA and in other regions of the World’s Ocean (e.g., N. Pacific; Venrick, 1974; Karl et al, 2012) fuels the surrounding community (biological pump) and is thought to support an efficient C export to the deep (Cooley and Yager, 2006; Cooley et al, 2007; Subramaniam et al, 2008; Yeung et al, 2012), determining the causal relationships between abundance and measured variables is of primary interest.…”