The balance between nitrogen fixation and denitrification on vegetated and non‐vegetated intertidal sediments

Russell, Douglas; Warry, Fiona Y.; Cook, Perran

doi:10.1002/lno.10353

Cited by 32 publications

(53 citation statements)

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“…δ 15 N values next to zero or slightly positive are consistent with nitrogen fixation as the main nitrogen source for these plants, as often reported for seagrass tissues (Hemminga and Mateo, 1996;Kennedy et al, 2004;Papadimitriou et al, 2005;Garcias-Bonet et al, 2016). There was no relationship between the δ 15 N composition of the seagrass tissues and their C/N ratio, which were expected from relationships between nitrogen fixation rates, which affect the δ15N composition of the plants, and their C/N ratio reported in the past (Cook et al, 2015;Russell et al, 2016). Seagrass, macroalgae, and mangroves showed a trend toward declining nitrogen isotopic values from south to north, spanning from positive (+3 to +15‰) values in the south to values around 0 to +1‰ in the Northern Red Sea (Figure 4).…”

Section: Discussionsupporting

confidence: 82%

Stable Isotope (δ13C, δ15N, δ18O, δD) Composition and Nutrient Concentration of Red Sea Primary Producers

et al. 2018

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Measurements of isotopic composition of marine primary producers are a valuable tool to follow and trace the source and cycling of organic matter in the marine systems, as well to describe the physiological status of aquatic photosynthetic organisms. Although stable isotope data abounds in the literature, relatively limited information regarding the isotopic signatures of marine primary producers is available for the Red Sea. Here we present data on carbon concentration (and nitrogen when possible) of phytoplankton, macroalgae, seagrasses, mangroves and salt-marsh plants, and examine how their isotopic signatures differed among plant types across a north-south gradient in the Red Sea. We also tested the potential use of deuterium, δD, to distinguish among primary producers whose carbon isotopic values may overlap. Our findings showed a clear differentiation of carbon and nitrogen content between the different groups of primary producers, as well as between species. Seagrasses and mangroves had on average larger carbon (30 and 49% of C, respectively) and nitrogen content (1.8% N) than other groups. In terms of stable carbon isotopes, seagrasses, and macroalgae tended to be heavier (−7.3 and −13.3‰, respectively) than halophytes, mangroves, and phytoplankton, which showed statistically similar and lighter δ 13 C values (between −24 and −26‰). There was a tendency for the nitrogen isotopic composition of seagrass and macroalgae to become lighter from the southern to the northern Red Sea, in parallel to a decline in nitrogen concentration in the tissues, indicative of a higher dependence of nitrogen fixation as a source of nitrogen toward the more oligotrophic northern Red Sea. Our results showed an overlap in the δ 13 C and δ 15 N values between macroalgae and seagrasses; however, their δD values were significantly different (seagrasses −56.6 ± 2.8‰ and macroalgae −95.7 ± 3.4‰). This remarkable difference offers a promising alternative for ecological studies where a similar range of isotopic values could mask different potential sources.

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Section: Discussionsupporting

confidence: 82%

Stable Isotope (δ13C, δ15N, δ18O, δD) Composition and Nutrient Concentration of Red Sea Primary Producers

et al. 2018

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“…At all these sites, the seagrass δ 15 N was < 6.5‰ and therefore assimilation of marine nitrogen from the water column is unlikely to explain the , it is unlikely that significant nitrogen assimilation was taking place from the water column. Taken together we suggest there is very limited direct assimilation of nitrogen from the water column, which is consistent with the low concentrations of inorganic nitrogen in the water column in this region (Russell et al, 2016), and is in agreement with a previous study of seagrass nitrogen sources at an open coastal site (McGlathery et al, 2001). 10 2.…”

Section: Potential Isotopic Effects Associated With Vegetative Assimisupporting

confidence: 93%

“…Whilst benthic primary producers such as seagrass can create micro-oxic zones deeper within the sediment that by diffusive transport alone (Brodersen et al, 2015;Frederiksen and Glud, 2006), these same seagrasses will also be actively competing with the nitrifiers for bioavailable nitrogen (Vonk et al, 2008). Consistent with this we have measured negligible rates of nitrification coupled to denitrification in intact cores with 15 N-NH 4 + tracer injected into the 20 sediment (Russell et al, 2016). Based on the previous discussion in section 4.1 then, it is most likely that the isotopic enrichment of the porewater compared to the sediment is the result of isotopic fractionation during assimilation by plant roots.…”

Section: Isotopic Signatures Of the Sediment Pool Relative To The Porsupporting

confidence: 71%

“…CC BY 4.0 License. mean contributions of ~15% by (Russell et al, 2016). We therefore suggest it is unlikely that nitrogen fixation can account for all of the isotopic depletion generally observed within the seagrass relative to the porewater, although we cannot rule out a small contribution.…”

Section: Potential Isotopic Effects Associated With Vegetative Assimimentioning

confidence: 74%

“…Whereas, the sites selected from Western Port have been previously described in al., 2016). For Western Port, terrestrial sources of nitrogen from the rivers contribute ~650 tonnes TN per year (Russell et al, 2016).…”

Section: Study Areamentioning

confidence: 99%

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Negligible isotopic fractionation of nitrogen within temperate <i>Zostera</i> spp. meadows

Russell¹,

Wong²,

Cook³

2018

Preprint

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Abstract. Seagrass meadows form an ecologically important ecosystem in the coastal zone. Excessive nitrogen inputs to the coastal zone pose a key threat to seagrass through eutrophication and associated algal overgrowth. The 15 N/ 14 N ratio of seagrass is commonly used to assess extent to which sewage derived nitrogen may be influencing seagrass beds. There have however, been no studies comparing the 15 N/ 14 N ratios of seagrass beds, their associated sediments and of critical importance, the porewater NH 4 + pool, which is most bioavailable. Here, we undertook a study of the 15 N/ 14 N ratios of 10 seagrass tissue, sediment porewater NH 4 + pool and the sediment solid phase to elucidate the extent of any fractionating processes taking place during organic matter mineralisation and nitrogen assimilation. The study was undertaken within two coastal embayments known to receive nitrogen from a range of sources including marine, urban and sewage sources. The

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In situ differences in nitrogen cycling related to presence of submerged aquatic vegetation in a Gulf of Mexico estuary

et al. 2022

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Estuaries provide a suite of ecosystem services to people but are also under heavy stress from human development including excess nutrient loading and alterations in benthic habitat that affect nutrient cycling. Here we examine the interaction of two important and common ecosystem management priorities in estuaries: limiting eutrophication and restoration of submerged aquatic vegetation (SAV). Rates of benthic nitrogen processing can vary by habitat type and there is need for more complete data on the contribution of SAV to overall nitrogen cycling in estuaries, as well as a need to examine nitrogen cycling in situ to better characterize the role of SAV areal coverage in mediating estuarine eutrophication. We compare nitrogen cycling between two common and adjacent habitat types (SAV and adjacent bare sediment [BS]) in an index coastal estuary using an in situ chamber‐based approach to better capture realized habitat differences. We also examined genomic community structure of sediment bacteria and archaea to identify biological indicators of nitrogen exchange. Both mean sediment–water exchange of dissolved N2 and microbial functional community structure differed between SAV and BS. Habitat differences were more consistent with lower variability at locations with low salinity and when sediment organic content was highest, which aligns with findings in other studies. Habitat types differed significantly in microbial composition, including functional groups and genes, like nifH, that may contribute to observed differences in nitrogen cycling. Overall, habitat type appeared most important to nitrogen cycling near the river mouth where sediment nitrogen was higher, and this information has implications for integrated management of habitat restoration/conservation and nutrient loading.

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The balance between nitrogen fixation and denitrification on vegetated and non‐vegetated intertidal sediments

Cited by 32 publications

References 71 publications

Stable Isotope (δ13C, δ15N, δ18O, δD) Composition and Nutrient Concentration of Red Sea Primary Producers

Stable Isotope (δ13C, δ15N, δ18O, δD) Composition and Nutrient Concentration of Red Sea Primary Producers

Negligible isotopic fractionation of nitrogen within temperate <i>Zostera</i> spp. meadows

In situ differences in nitrogen cycling related to presence of submerged aquatic vegetation in a Gulf of Mexico estuary

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The balance between nitrogen fixation and denitrification on vegetated and non‐vegetated intertidal sediments

Cited by 32 publications

References 71 publications

Stable Isotope (δ13C, δ15N, δ18O, δD) Composition and Nutrient Concentration of Red Sea Primary Producers

Stable Isotope (δ13C, δ15N, δ18O, δD) Composition and Nutrient Concentration of Red Sea Primary Producers

Negligible isotopic fractionation of nitrogen within temperate &lt;i&gt;Zostera&lt;/i&gt; spp. meadows

In situ differences in nitrogen cycling related to presence of submerged aquatic vegetation in a Gulf of Mexico estuary

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Negligible isotopic fractionation of nitrogen within temperate <i>Zostera</i> spp. meadows