Burrowing deeper into benthic nitrogen cycling: the impact of bioturbation on nitrogen fixation coupled to sulfate reduction

Bertics, Victoria J.; Sohm, Jill A.; Treude, Tina; Chow, Cheryl-Emiliane T.; Capone, Douglas C.; Fuhrman, Jed A.; Ziebis, Wiebke

doi:10.3354/meps08639

Cited by 155 publications

(115 citation statements)

References 92 publications

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“…Many physical and biological factors influence the level of nutrient enrichment, as well as the type and severity of consequences to an ecosystem's functioning. Nutrient cycling and efflux from the sediments are influenced by the sedimentary environment (Blackburn and Henriksen, 1983;Glud, 2008;Santos et al, 2012), benthic macrofauna (Bertics et al, 2010;Laverock et al, 2011), and macrophyte communities (Kenworthy et al, 1982). Our results show that primary consideration should be given to benthic macrofauna and sediment properties when estimating potential enrichment levels of experiments.…”

Section: Discussionmentioning

confidence: 83%

In situ soft sediment nutrient enrichment: A unified approach to eutrophication field experiments

Douglas

Pilditch

Hines

et al. 2016

Marine Pollution Bulletin

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Adding fertiliser to sediments is an established way of studying the effects of eutrophication but a lack of consistent methodology, reporting on enrichment levels, or guidance on application rates precludes rigorous synthesis and meta-analysis. We developed a simple enrichment technique then applied it to 28 sites across an intertidal sandflat. Fertiliser application rates of 150 and 600 g N m −2 resulted in pore water ammonium concentrations respectively 1-110 and 4-580 × ambient, with greater elevations observed in deeper (5-7 cm) than surface (0-2 cm) sediments. These enrichment levels were similar to eutrophic estuaries and were maintained for at least seven weeks. The high between-site variability could be partially explained by the sedimentary environment and macrofaunal community (42%), but only at the high application rate. We suggest future enrichment studies should be conducted in situ across large environmental gradients to incorporate real world complexity and increase generality of conclusions.

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Section: Discussionmentioning

confidence: 83%

In situ soft sediment nutrient enrichment: A unified approach to eutrophication field experiments

Douglas

Pilditch

Hines

et al. 2016

Marine Pollution Bulletin

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“…The distribution of N 2 fixation rates were generally similar to nitrification -with much lower rates (8-45 nmol cm −3 yr −1 ) at site 4A -again consistent with overall lower cell abundance (Zhao and Jørgensen, 2015). These rates are 2-3 orders of magnitude lower than rates measured in coastal and estuarine sediments (e.g., Bertics et al, 2010;Rao and Charette, 2012;Joye and Paerl, 1993), although still much higher than rates measured in studies of N 2 fixation in oligotrophic water column (e.g., Montoya et al, 2004;Capone et al, 2005). Overall, North Pond sediments appear to harbor a spectrum of microbially mediated N transformations, with rates lower than those found in most sedimentary systems, yet still generally higher than those observed in overlying oligotrophic waters.…”

Section: Model-predicted Values Of δ 15 N Ntr : Implications For N Somentioning

confidence: 83%

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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“…Based on our findings, a naïve hypothesis would be that the frequency of physical disturbance (here, bottom fishing) is less important for biogeochemical cycling in cohesive sediments than it is in noncohesive sediments, but in the absence of a comparable fully functional ecosystem such a conclusion is premature (Thrush and Dayton 2002). Indeed, even a low frequency of disturbance can cause significant changes to the biotic and abiotic components of the system and it is possible that intensive fishing disturbance can cause a reduction of [NO 3 -N] that relates to over-mobilisation of sediment, increased microbial activity, and net loss of N from the sediments (Bertics et al 2010, Laverock et al 2011). Whilst it is clear that non-cohesive sediment communities are vulnerable to changes in the frequency of fishing, even though the fishing pressure is relatively low, near-bed current flows and the permeability of the sediment profile mean that organic carbon cycling is already rapid (Rocha 2008), making it difficult to assess how nutrient sediment-water exchange is affected as communities are modified.…”

Section: Discussionmentioning

confidence: 98%

Mediation of macronutrients and carbon by post-disturbance shelf sea sediment communities

et al. 2017

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Benthic communities play a major role in organic matter remineralisation and the mediation of many aspects of shelf sea biogeochemistry. Few studies have considered how changes in community structure associated with different levels of physical disturbance affect sediment macronutrients and carbon following the cessation of disturbance. Here, we investigate how faunal activity (sediment particle reworking and bioirrigation) in communities that have survived contrasting levels of bottom fishing affect sediment organic carbon content and macronutrient concentrations ([NH 4 [NH 4 -N] increases in noncohesive sediments that have experienced a higher frequency of fishing. Further analyses reveal that the way communities are restructured by physical disturbance differs between sediment type and with fishing frequency, but that changes in community structure do little to affect bioturbation and associated levels of organic carbon and nutrient concentrations. Our results suggest that in the presence of physical disturbance, irrespective of sediment type, the mediation of macronutrient and carbon cycling increasingly reflects the decoupling of organism-sediment relations. Indeed, it is the traits of the species that reside at the sediment-water interface, or that occupy deeper parts of the sediment profile, that are disproportionately expressed post-disturbance, that are most important for sustaining biogeochemical functioning.

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Burrowing deeper into benthic nitrogen cycling: the impact of bioturbation on nitrogen fixation coupled to sulfate reduction

Cited by 155 publications

References 92 publications

In situ soft sediment nutrient enrichment: A unified approach to eutrophication field experiments

In situ soft sediment nutrient enrichment: A unified approach to eutrophication field experiments

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

Mediation of macronutrients and carbon by post-disturbance shelf sea sediment communities

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