Under anaerobic conditions, it is widely assumed that nitrate (NO3-) and nitrite (NO2-) reduction is primarily the result of microbial respiration (Burgin and Hamilton, 2007; Granger et al., 2008). However, it is also proven that the abiotic reduction of nitrate and nitrite by reduced iron(II) (Fe(II)), whether mineral-bound or surface-associated, may also occur under certain environmentally relevant conditions (Chao and Kroontje, 1966; Straub et al., 1996; Picardal, 2012,). With a range of experimental conditions, nitrogen and oxygen stable isotope systematics of abiotic nitrite reduction by Fe(II) were investigated in an effort to characterize the biotic and abiotic processes in the environment. While homogenous reactions between NO2- and Fe(II) in artificial seawater (ASW) showed little reduction, heterogeneous reactions involving Fe-containing minerals showed considerable nitrite loss. Specifically, rapid nitrite reduction was observed in experiments that included reduced nontronite clay and an Fe(II)-Fe(III) hydroxide mineral, termed green rust. These iron oxides and clay minerals offer both a source of reduced iron in the mineral matrix as well as a surface for Fe(II) activation. Additional control experiments with corundum as a non-Fe containing mineral surface showed little NO2- loss, implicating a more dominant role of structural iron in the clays during nitrite reduction. In experiments with nontronite and green rust the isotope effects (15ε and 18ε) ranged from 3 to 16‰ for 15ε and 2 to 6‰ for 18ε. Nitrite reduction rates and 15ε values within an experimental condition were directly correlated with slower reactions having higher isotopic fractionation. The apparent 18ε was affected by oxygen atom exchange with water, which lowered the isotope effect. Although little data exist for comparison with the dual isotopes of microbial NO2- reduction, these data serve as a benchmark for evaluating the role of abiotic processes in nitrogen (N) reduction, particularly in sediment systems low in organic carbon and high in reduced iron. / Engineering Sciences
| Identifer | oai:union.ndltd.org:harvard.edu/oai:dash.harvard.edu:1/17417576 |
| Date | 16 July 2015 |
| Creators | Grabb, Kalina C. |
| Publisher | Harvard University |
| Source Sets | Harvard University |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation, text |
| Format | application/pdf |
| Rights | open |
Page generated in 0.0018 seconds