Benthic fluxes and pore water studies from sediments of the central equatorial north Pacific: Nutrient diagenesis

Berelson, William M.; Hammond, Douglas E.; O'Neill, D.J.; Xu, Xin; Chin, Carol S.; Zukin, Jeffrey G.

doi:10.1016/0016-7037(90)90117-4

Cited by 110 publications

(52 citation statements)

References 31 publications

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“…(Ziebis et al, 2012). At all depths in all three profiles, porewater NO (Ziebis et al, 2012), consistent with other studies of NO − 3 fluxes in pelagic deep-sea sediments (Berelson et al, 1990;Goloway and Bender, 1982;Hammond et al, 1996;Jahnke et al, 1982;Grundmanis and Murray, 1982). More precisely, below the sediment-water interface, NO − 3 concentrations increased significantly with depth ( Fig.…”

Section: Previous Measurements Of Dissolved Oxygen and Organic Mattersupporting

confidence: 90%

“…In particular, the distribution of dissolved substrates that are available as electron acceptors for microbial respiration of organic carbon, generally reflect stepwise consumption by the most thermodynamically (and kinetically) favorable metabolic processes (e.g., O 2 consumption precedes NO − 3 consumption, which precedes sulfate reduction). While in organic-rich estuarine and continental shelf sediments, dissolved O 2 and NO (Berelson et al, 1990;Christensen and Rowe, 1984;D'Hondt et al, 2009;Goloway and Bender, 1982;Seitzinger et al, 1984). In organic-rich sediments, NO − 3 concentration profiles may exhibit maxima only a few millimeters or centimeters below the sedimentwater interface.…”

Section: Model-estimated Rates Of Nitrification and Denitrificationmentioning

confidence: 99%

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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: Previous Measurements Of Dissolved Oxygen and Organic Mattersupporting

confidence: 90%

Section: Model-estimated Rates Of Nitrification and Denitrificationmentioning

confidence: 99%

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

et al. 2015

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“…Diffusive benthic fluxes-Two types of approaches are generally applied to measure fluxes of any component across the sediment-water interface: (1) measurements of gradients in the sediment and/or water column (e.g., Broecker 1965;Hesslein 1976;Key et al 1979;Gruebel and Martens 1984;Berelson et al 1990); and (2) in situ benthic chambers (e.g., Martens et al 1980;Gruebel and Martens 1984;Berelson et al 1990). In addition, Martens et al (1980) described a depth-independent mathematical approach specifically for the determination of diffusive fluxes of 222 Rn.…”

Section: Experimental Methodsmentioning

confidence: 99%

Estimating the groundwater contribution into Florida Bay via natural tracers, ²²²Rn and CH₄

Corbett

Dillon

Burnett

et al. 2000

Limnology & Oceanography

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Groundwater may represent a significant pathway for nutrients and other dissolved solutes into Florida Bay, especially near the Keys where wastewater disposal practices add large amounts of nitrogen and phosphorus to the subsurface each year. Previously, we suggested that high water column inventories of the tracers 222 Rn and CH 4 may be indicative of groundwater discharge. In this study, we employed mass balance calculations to determine that the total benthic fluxes required to maintain the measured water column tracer inventories were significantly larger than diffusive fluxes and varied between 4.2-5.6 dpm m Ϫ2 min Ϫ1 and 5.8-15.4 nmoles m Ϫ2 min Ϫ1 for 222 Rn and CH 4 , respectively. Independent estimates of the diffusive flux and porewater activities/concentrations allowed us to calculate an advective groundwater velocity, assuming that the difference between the total benthic flux (given above) and the diffusive flux is driven by seepage-driven porewater advection. These calculated velocities ranged from 0.2 to 4.3 cm d Ϫ1 for all sites, tracers, and sampling periods, with a best estimate of approximately 1.7 cm d Ϫ1. These estimates of groundwater velocities compare very well with previous measurements of groundwater flux (1-3 cm d Ϫ1 ) at the same sites via seepage meters.Florida Bay, a mosaic of shallow water banks and deeper water basins, was once characterized by clear waters and healthy seagrass meadows. Massive seagrass die-offs, planktonic algal blooms, and salinity excursions have occurred in the last decade (Boesch et al. 1993;Phlips et al. 1995;Phlips and Badylak 1996;Phlips et al. 1999;Fourqurean and Robblee 1999). There is no simple answer available for what has caused these dramatic events, but it is certain that they are related to a combination of natural phenomena and anthropogenic activities. A better understanding of the complete hydrologic and nutrient budget of Florida Bay is essential for interpreting past and current change, as well as for development of good management strategies for this and other coastal systems.Some patterns of ecological change and environmental degradation in Florida Bay point to increased nutrient loading as one likely cause (Lapointe et al. 1990). However, the sources and pathways of these hypothesized nutrient additions are not clear. Nutrient inputs to the bay include freshwater flowing from the Everglades, Gulf of Mexico waters flowing into the bay, atmospheric deposition, and local sources (Rudnick et al. 1999). Localized inputs include diffusion from sediments, nutrient release during sediment re-

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“…60%) (Sayles et al, 2001). The artifact presumably reflects adsorption of dissolved SiO 2 from solutions originating at depth (high concentrations) as these solutions from deeper beds pass through terrigenous material previously equilibrated with low concentrations characteristic of shallow sediment depth (Berelson et al,1990a;Martin et al, 1991). That the effect is not observed in biogenic silica-rich sediments where shallow versus deep concentration differences are the greatest implies very limited surface reactivity of the particles.…”

Section: Pore-water Sampling and Profilingmentioning

confidence: 88%

“…In addition to artifacts which generally affect extraction of pore waters from sediments, there are also artifacts specific to particular sampling methods. NO 3 2 in pore water obtained by centrifugation is believed to be somewhat enriched above true values in the upper 0.5 -3 cm of sediments (Berelson et al, 1990a;Martin and McCorkle, 1993); the mechanism for this enrichment is unknown. SiO 2 concentrations in at least some sediments are modified during wcs processing onboard ship (Berelson et al, 1990a;Martin et al, 1991).…”

Section: Pore-water Sampling and Profilingmentioning

confidence: 99%

The Recycling of Biogenic Material at the Sea Floor

Martin

Sayles

2014

Treatise on Geochemistry

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Benthic fluxes and pore water studies from sediments of the central equatorial north Pacific: Nutrient diagenesis

Cited by 110 publications

References 31 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

Estimating the groundwater contribution into Florida Bay via natural tracers, ²²²Rn and CH₄

The Recycling of Biogenic Material at the Sea Floor

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Benthic fluxes and pore water studies from sediments of the central equatorial north Pacific: Nutrient diagenesis

Cited by 110 publications

References 31 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

Estimating the groundwater contribution into Florida Bay via natural tracers, 222Rn and CH4

The Recycling of Biogenic Material at the Sea Floor

Contact Info

Product

Resources

About

Estimating the groundwater contribution into Florida Bay via natural tracers, ²²²Rn and CH₄