Constraining the role of iron in environmental nitrogen transformations. Dual stable isotope systematics of abiotic NO₂- reduction by Fe(II) and its production of N₂O

Technical Report · Wed Sep 16 00:00:00 EDT 2015

DOI:https://doi.org/10.2172/1214871· OSTI ID:1214871

Johnston, David ^[1]; Wankel, Scott David ^[2]; Buchwald, Carolyn ^[2]; Hansel, Colleen ^[2]

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1. Harvard Univ., Cambridge, MA (United States)
2. Woods Hole Oceanographic Inst., MA (United States)

Redox reactions involving nitrogen and iron have been shown to have important implications for mobilization of priority contaminants. Thus, an understanding of the linkages between their biogeochemical cycling is critical for predicting subsurface mobilization of radionuclides such as uranium. Despite mounting evidence for biogeochemical interactions between iron and nitrogen, our understanding of their environmental importance remains limited. Here we present an investigation of abiotic nitrite (NO₂^-) reduction by Fe(II) or ‘chemodenitrification,’ and its relevance to the production of nitrous oxide (N₂O), specifically focusing on dual (N and O) isotope systematics under a variety of environmentally relevant conditions. We observe a range of kinetic isotope effects that are regulated by reaction rates, with faster rates at higher pH (~8), higher concentrations of Fe(II) and in the presence of mineral surfaces. A clear non-linear relationship between rate constant and kinetic isotope effects of NO₂^- reduction was evident (with larger isotope effects at slower rates) and is interpreted as reflecting the dynamics of Fe(II)-N reaction intermediates. N and O isotopic composition of product N₂O also suggests a complex network of parallel and/or competing pathways. Our findings suggest that NO₂^- reduction by Fe(II) may represent an important abiotic source of environmental N₂O, especially in iron-rich environments experiencing dynamic redox variations. This study provides a multi-compound, multi-isotope framework for evaluating the environmental occurrence of abiotic NO₂^- reduction and N₂O formation, helping future studies constrain the relative roles of abiotic and biological N₂O production pathways.

• Research Organization: Harvard Univ., Cambridge, MA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• DOE Contract Number: SC0006681
• OSTI ID: 1214871
• Report Number(s): SC0006681
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
nitrogen
iron
redox
stable isotope
nitrous oxide
nitrite