Nitrogen Uptake, Dissolved Organic Nitrogen Release, and New Production

Bronk, Deborah A.; Glibert, Patricia M.; Ward, Bess B.

doi:10.1126/science.265.5180.1843

Cited by 378 publications

(228 citation statements)

References 19 publications

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“…The slope of the relationship (4.72) is somewhat lower, but not significantly so, than the expected Redfield C/N ratio of 6.6 (Redfield 1958). However, the intercept of the relationship was significantly greater than 0 (t-test, P ϭ 0.028), suggesting the existence of other sources of nitrogen for phytoplankton uptake than those investigated here, and/or the release of dissolved organic nitrogen (Bronk et al 1994).…”

Section: Resultsmentioning

confidence: 90%

Nitrate uptake and diffusive nitrate supply in the Central Atlantic

Planas

Agustı́

Duarte

et al. 1999

Limnology & Oceanography

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The latitudinal variation (35ЊS to 28ЊN) in the rate of diffusive nitrate supply across the thermocline and the associated variation in the uptake rate of nitrate and ammonium in the Central Atlantic was studied. The calculated diffusive nitrate flux showed a sharp latitudinal gradient, with the lowest nitrate supply (0.00037 mol m Ϫ3 d Ϫ1 ) in the South Atlantic subtropical gyre and the highest values (23.5 mol m Ϫ3 d Ϫ1 ) between the Equator and 15ЊN. The uptake rate of nitrate was inhibited at high irradiance at most stations. Both nitrate and ammonium uptake rates were lowest (about 3 and 10 mol m Ϫ3 d Ϫ1 , respectively) at the southern end of the transect and increased (about 20 and 55 mol m Ϫ3 d Ϫ1 , respectively) towards the Equator, with this increase being much greater for ammonium than for nitrate uptake. The f-ratio was highest (ഠ0.4) just south of the Equator and lowest (ഠ0.03) at the southern end of the transect. The slope between total uptake rate of dissolved inorganic nitrogen and gross primary production, calculated from O 2 -based measurements, in surface waters (4.72 Ϯ 1.54) was somewhat lower, but not significantly so, than the expected C/N ratio of 6.6. The average uptake rate of nitrate did not differ significantly from the average estimated diffusive supply of nitrate to the biogenic layer over the Central Atlantic. However, the nitrate uptake rate increased as the ⅓ power of the diffusive nitrate flux to the biogenic layer. As a result, nitrate uptake far exceeded (by up to 100-fold) the nitrate flux to the biogenic layer in the stations where the supply of nitrate was lowest. The excess nitrate uptake averaged 0.65 Ϯ 0.24 mmol NO 3 m Ϫ2 d Ϫ1 (range, 0.05-1.9 mmol NO 3 m Ϫ2 d Ϫ1 ), which must be supplied through atmospheric deposition and other perturbation events. This excess nitrate uptake is relatively large compared to the diffusive supply in the most unproductive areas, where external nitrate inputs fuel the new production. In contrast, these sources of nitrate are far less significant where high diffusive fluxes suffice to maintain high nitrate uptake rates.

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Section: Resultsmentioning

confidence: 90%

Nitrate uptake and diffusive nitrate supply in the Central Atlantic

Planas

Agustı́

Duarte

et al. 1999

Limnology & Oceanography

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“…Few studies have quantified the amounts of C or N that flux into, and out, of the DOM pool relative to the other major C and N pools. Those that have provide an incomplete picture of DOM cycling as they often cannot distinguish between the individual sources and sinks of DOM (Bronk et al, 1994(Bronk et al, , 1998. Additionally, as far as we are aware, there are no long-term time series measurements of the C and N flux through the DOM pool that adequately describe the annual DOM cycle.…”

Section: Introductionmentioning

confidence: 99%

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

Keller

Hood

2011

Ecological Modelling

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a b s t r a c tIn this paper we investigate the seasonal autochthonous sources of dissolved organic carbon (DOC) and nitrogen (DON) in the euphotic zone at a station in the upper Chesapeake Bay using a new mass-based ecosystem model. Important features of the model are: (1) carbon and nitrogen are incorporated by means of a set of fixed and varying C:N ratios; (2) dissolved organic matter (DOM) is separated into labile, semi-labile, and refractory pools for both C and N; (3) the production and consumption of DOM is treated in detail; and (4) seasonal observations of light, temperature, nutrients, and surface layer circulation are used to physically force the model. The model reasonably reproduces the mean observed seasonal concentrations of nutrients, DOM, plankton biomass, and chlorophyll a. The results suggest that estuarine DOM production is intricately tied to the biomass concentration, ratio, and productivity of phytoplankton, zooplankton, viruses, and bacteria. During peak spring productivity phytoplankton exudation and zooplankton sloppy feeding are the most important autochthonous sources of DOM. In the summer when productivity peaks again, autochthonous sources of DOM are more diverse and, in addition to phytoplankton exudation, important ones include viral lysis and the decay of detritus. The potential importance of viral decay as a source of bioavailable DOM from within the bulk DOM pool is also discussed. The results also highlight the importance of some poorly constrained processes and parameters. Some potential improvements and remedies are suggested. Sensitivity studies on selected parameters are also reported and discussed.

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“…Although the key role of labile DOC and DON in the regeneration and new production of marine systems is recognised nowadays (e.g. Bronk, Glibert, & Ward, 1994;Hansell & Carlson, 1998), it has not been incorporated yet into debates about the fate of phytogenic materials in the coastal zone. Horizontal transport of recently produced POM susp and DOM to the adjacent relatively barren offshore waters constitutes an alternative route for the export of organic materials produced along ocean margins.…”

Section: Net Consumption Of Nomentioning

confidence: 99%

Off-shelf fluxes of labile materials by an upwelling filament in the NW Iberian Upwelling System

Álvarez-Salgado

Doval

Borges

et al. 2001

Progress in Oceanography

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Daily changes in the concentrations of carbon and nitrogen species were monitored during the course of a Lagrangian drifter experiment in a recurrent upwelling filament south of Cape Finisterre (NW Iberian Upwelling System). A drifting buoy released at the southern edge of the upwelling centre generated by the Cape moved 60km southwestwards from 3 to 7 August 1998. Organic matter in the 50m deep study water mass (average 77±2 µM C) consisted of: 57µM C of dissolved organic matter (DOM) with a C/N molar ratio of 19±2; 6µM C of DOM with a C/N ratio of 9±2, and 14µM C of 50% DOM and 50% suspended organic matter (POM susp ) with a C/N ratio of 6.0±0.4.Net conversion of consumed inorganic salts into accumulated TOM=POM susp +DOM was ෂ40% for nitrogen and ෂ30% for carbon. Since the parcel of water crossed the shelf-edge, these conversion efficiencies are equivalent to net horizontal export-ratio of 0.4 and 0.3 respectively. A second drifter was deployed in the offshore-end of the filament, and was displaced 20km west between 14 and 17 August 1998. Nitrate was exhausted in the surface water and no significant changes were observed in the variables measured during the course of the second experiment. Low C/N ratios (6.5±0.4) and rapid POM susp /DOM inter-conversion in the 20 µM C excess observed in the study volume points to the persistence of the labile materials formed on the shelf during transport to the ocean. Our data demonstrate a) the key role of upwelling filaments in off-shelf export of organic materials and b) the major contribution of DOM to this horizontal export, a previously unaccounted amount.The high nitrogen content of the materials exported make them attractive organic substrates for use by microbial populations in the adjacent oligotrophic ocean. 

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Nitrogen Uptake, Dissolved Organic Nitrogen Release, and New Production

Cited by 378 publications

References 19 publications

Nitrate uptake and diffusive nitrate supply in the Central Atlantic

Nitrate uptake and diffusive nitrate supply in the Central Atlantic

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

Off-shelf fluxes of labile materials by an upwelling filament in the NW Iberian Upwelling System

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