Community N and O isotope fractionation by sulfide-dependent denitrification and anammox in a stratified lacustrine water column

Wenk, Christine B.; Zopfi, Jakob; Blees, Jan; Veronesi, Mauro; Niemann, Helge; Lehmann, Moritz F.

doi:10.1016/j.gca.2013.10.034

Cited by 63 publications

(57 citation statements)

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“…While rates of nitrification were less sensitive (somewhat higher in the upper layers of 4A), this very low prescribed value of 15 ε DNF often lead to dramatically increased estimates of denitrification rates -in particular in the upper transitional layers of profiles at 2B and 3D where ∼ 10-20-fold higher maximum denitrification rates are required to reconcile nitrate concentration and isotope data ( In the anoxic intervals, estimated values of 18 ε : 15 ε DNF ranged from 0.83 to 1.11 with an average value of 0.99 ± 0.1 (Table 2), consistent with a prominent role of respiratory nitrate reductase (Nar), which imparts a 18 ε : 15 ε DNF of ∼ 0.96 ± 0.01 (Granger et al, 2008). Notably, however, the lower values of 0.86 and 0.83 observed near the top and the core of the anoxic zone in site 2B could suggest influence of nitrate reduction by periplasmic nitrate reductase (Nap) (Granger et al, 2008) and chemolithotrophic NO − 3 reduction (Frey et al, 2014;Wenk et al, 2014), which has been shown to impart a lower 18 ε : 15 ε DNF closer to 0.6. In this particular interval, this could suggest that as much as 43 % of nitrate reduction is chemolithotrophic and perhaps metabolically linked to the oxidation of inorganic substrates such as reduced iron or sulfur species.…”

Section: Model Sensitivity To Prescribed 15 ε Dnf In Transitional Intsupporting

confidence: 52%

“…Moreover, although the relationship between the kinetic isotope effects for 18 O and 15 N during respiratory consumption of NO − 3 by denitrification (e.g., 18 ε : 15 ε DNF ) has been shown to remain consistent at 1:1, the potential influence of nitrate reduction by periplasmic nitrate reductase (Nap, periplasmic nitrate reductase. ), which imparts a lower 18 ε : 15 ε DNF value of 0.6 (Granger et al, 2008;Frey et al, 2014), could play a role in the dual isotope trajectory of NO − 3 consumption (Wenk et al, 2014). Further, in the absence of NH + 4 accumulation in these sediments, the δ 15 N NTR is equal to the source of NH + 4 being oxidized to NO − 3 , which is related to the δ 15 N of the organic matter being remineralized.…”

Section: Diffusion-reaction Modelmentioning

confidence: 96%

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Nitrogen cycling in the deep sedimentary biosphere: nitrate isotopes in porewaters underlying the oligotrophic North Atlantic

et al. 2015

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Abstract. Nitrogen (N) is a key component of fundamental biomolecules. Hence, its cycling and availability are central factors governing the extent of ecosystems across the Earth. In the organic-lean sediment porewaters underlying the oligotrophic ocean, where low levels of microbial activity persist despite limited organic matter delivery from overlying water, the extent and modes of nitrogen transformations have not been widely investigated. Here we use the N and oxygen (O) isotopic composition of porewater nitrate (NO − 3 ) from a site in the oligotrophic North Atlantic (Integrated Ocean Drilling Program -IODP) to determine the extent and magnitude of microbial nitrate production (via nitrification) and consumption (via denitrification). We find that NO − 3 accumulates far above bottom seawater concentrations (∼ 21 µM) throughout the sediment column (up to ∼ 50 µM) down to the oceanic basement as deep as 90 m b.s.f. (below sea floor), reflecting the predominance of aerobic nitrification/remineralization within the deep marine sediments. Large changes in the δ 15 N and δ 18 O of nitrate, however, reveal variable influence of nitrate respiration across the three sites. We use an inverse porewater diffusion-reaction model, constrained by the N and O isotope systematics of nitrification and denitrification and the porewater NO − 3 isotopic composition, to estimate rates of nitrification and denitrification throughout the sediment column. Results indicate variability of reaction rates across and within the three boreholes that are generally consistent with the differential distribution of dissolved oxygen at this site, though not necessarily with the canonical view of how redox thresholds separate nitrate regeneration from dissimilative consumption spatially. That is, we provide stable isotopic evidence for expanded zones of co-occurring nitrification and denitrification. The isotope biogeochemical modeling also yielded estimates for the δ 15 N and δ 18 O of newly produced nitrate (δ 15 N NTR (NTR, referring to nitrification) and δ 18 O NTR ), as well as the isotope effect for denitrification ( 15 ε DNF ) (DNF, referring to denitrification), parameters with high relevance to global ocean models of N cycling. Estimated values of δ 15 N NTR were generally lower than previously reported δ 15 N values for sinking particulate organic nitrogen in this region. We suggest that these values may be, in part, related to sedimentary N 2 fixation and remineralization of the newly fixed organic N. Values of δ 18 O NTR generally ranged between −2.8 and 0.0 ‰, consistent with recent estimates based on lab cultures of nitrifying bacteria. Notably, some δ 18 O NTR values were elevated, suggesting incorporation of 18 O-enriched dissolved oxygen during nitrification, and possibly indicating a tight coupling of NH + 4 and NO − 2 oxidation in this metabolically sluggish environment. Our findings indicate that the production of organic matter by in situ autotrophy (e.g., nitrification, nitrogen fixation) supplies a large fraction of the...

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Section: Model Sensitivity To Prescribed 15 ε Dnf In Transitional Intsupporting

confidence: 52%

Section: Diffusion-reaction Modelmentioning

confidence: 96%

Nitrogen cycling in the deep sedimentary biosphere: nitrate isotopes in porewaters underlying the oligotrophic North Atlantic

et al. 2015

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“…The nitrogen biogeochemistry of the recent years (2009–2011) in this lake basin has been investigated in detail (Wenk et al ), and sulfur‐driven denitrification was identified as the dominant fixed N removal process in the RTZ at mid water depth, whereas organotrophic denitrification seemed to be negligible. Denitrification in the RTZ, here defined as the zone between O 2 disappearance and H 2 S accumulation, led to a decrease in

{NO}_{3}^{-}

concentration from ∼30 μ mol L −1 at 20 m depth to zero levels within the RTZ (Fig.…”

Section: Resultsmentioning

confidence: 99%

Differential N₂ O dynamics in two oxygen-deficient lake basins revealed by stable isotope and isotopomer distributions

et al. 2016

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Lakes are a nitrous oxide (N2O) source to the atmosphere, but the biogeochemical controls and microbial pathways of N2O production are not well understood. To trace microbial N2O production (denitrification, nitrifier denitrification, and nitrification) and consumption (denitrification) in two basins of Lake Lugano, we measured the concentrations and N and O isotope compositions of N2O, as well as the intramolecular 15N distribution, i.e., site preference (SP). Our results revealed differential N2O dynamics in the two lake basins, with N2O concentrations between 12 nmol L−1 and > 900 nmol L−1 in the holomictic South Basin, and significantly lower concentrations in the meromictic North Basin (<13 nmol L−1). In the South Basin, the isotope signatures reflected a complex combination of N2O production by nitrifying bacteria through hydroxylamine (NH2OH) oxidation, N2O production through incomplete denitrification, and N2O reduction to N2, all occurring in close vicinity within the redox transition zone (RTZ). In the North Basin, in contrast, the N2O isotopomer signatures suggested that nitrifier denitrification was the main N2O source. The pronounced decrease in N2O concentrations to undetectable levels within the RTZ, in tandem with an increase in δ15N‐N2O, δ18O‐N2O, and SP indicated quantitative N2O consumption by microbial denitrification. In the northern basin this was primarily sulfide‐dependent. The apparent N and O isotope enrichment factors associated with net N2O consumption were 15ε ≈ 3.2‰ and 18ε ≈ 8.6‰, respectively. The according 18O to 15N enrichment ratio (18ε: 15ε ≈ 2.5) is consistent with previous reports for microbial N2O reduction, underscoring its robust nature across environments.

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“…Again, there is a lack of data on the isotopic expressions of these enzymes at the ecosystem level. Wenk et al (2014) attributed the low O : N isotopic effect of ∼ 0.89 to chemolithoautotrophic denitrification, rather than heterotrophic denitrification, in the northern basin of Lake Lugano.…”

Section: Denitrificationmentioning

confidence: 99%

Isotopic composition of nitrate and particulate organic matter in a pristine dam reservoir of western India: implications for biogeochemical processes

et al. 2017

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Abstract. Isotopic composition of nitrate (δ 15 N and δ 18 O) and particulate organic matter (POM; δ 15 N and δ 13 C) were measured in the Tillari Reservoir, located at the foothills of the Western Ghats, Maharashtra, western India. The reservoir, which is stratified during spring-summer and autumn seasons but gets vertically mixed during the southwest monsoon (SWM) and winter, is characterized by diverse redox nitrogen transformations in space and time. The δ 15 N and δ 18 O values of nitrate were low (δ 15 N = 2-10 ‰, δ 18 O = 5-8 ‰) during normoxic conditions but increased gradually (the highest at δ 15 N = 27 ‰, δ 18 O = 29 ‰) when anoxic conditions facilitated denitrification in the hypolimnion during spring-early summer. Once nitrate was fully utilized and sulfidic conditions set in, NH + 4 became the dominant inorganic N species, with δ 15 N ranging from 1.3 to 2.6 ‰. Low δ 15 N (∼ −5 ‰) and δ 13 C (−37 to −32 ‰) of POM cooccurring with high NH + 4 and CH 4 in sulfidic bottom waters were probably the consequence of microbial chemosynthesis. Assimilation of nitrate in the epilimnion was the major controlling process on the N isotopic composition of POM (δ 15 N = 2-6 ‰). Episodic low δ 15 N values of POM (−2 to 0 ‰) during early summer, coinciding with the absence of nitrate, might arise from N fixation, although further work is required to confirm the hypothesis. δ 13 C POM in the photic zone ranged between −29 and −27 ‰ for most parts of the year. The periods of mixing were characterized by uniform δ 15 N-NO

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Community N and O isotope fractionation by sulfide-dependent denitrification and anammox in a stratified lacustrine water column

Cited by 63 publications

References 58 publications

Nitrogen cycling in the deep sedimentary biosphere: nitrate isotopes in porewaters underlying the oligotrophic North Atlantic

Nitrogen cycling in the deep sedimentary biosphere: nitrate isotopes in porewaters underlying the oligotrophic North Atlantic

Differential N₂ O dynamics in two oxygen-deficient lake basins revealed by stable isotope and isotopomer distributions

Isotopic composition of nitrate and particulate organic matter in a pristine dam reservoir of western India: implications for biogeochemical processes

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Community N and O isotope fractionation by sulfide-dependent denitrification and anammox in a stratified lacustrine water column

Cited by 63 publications

References 58 publications

Nitrogen cycling in the deep sedimentary biosphere: nitrate isotopes in porewaters underlying the oligotrophic North Atlantic

Nitrogen cycling in the deep sedimentary biosphere: nitrate isotopes in porewaters underlying the oligotrophic North Atlantic

Differential N2 O dynamics in two oxygen-deficient lake basins revealed by stable isotope and isotopomer distributions

Isotopic composition of nitrate and particulate organic matter in a pristine dam reservoir of western India: implications for biogeochemical processes

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Differential N₂ O dynamics in two oxygen-deficient lake basins revealed by stable isotope and isotopomer distributions