Contrasting patterns of dissolved organic nitrogen release by two size fractions of estuarine plankton during a period of rapid NH/ consumption and N02-production

Bronk, D. A.; Glibert, Patricia M.

doi:10.3354/meps096291

Cited by 50 publications

(26 citation statements)

References 25 publications

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“…The nitrogen inventory of regions such as the North Atlantic is also influenced indirectly by atmospheric inputs, as iron associated with Saharan dust enhances diazotrophic nitrogen fixation, a source of new nitrogen to the surface ocean (Moore et al, 2009;Jickells and Moore, 2015). Although regenerated productivity has often been represented by, and measured as, NH + 4 assimilation, the significance of DON as a substrate for primary producers has become clearer, including the assimilation of urea and amino acids (Bronk and Glibert, 1993;Bronk and Ward, 1999;Wafar et al, 2004;Moschonas et al, 2015). However, the contribution to total production (i.e.…”

Section: R Clark Et Al: the Significance Of Nitrogen Regeneratiomentioning

confidence: 99%

The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

2016

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Abstract. The Lagrangian progression of a biological community was followed in a filament of the Mauritanian upwelling system, north-west Africa, during offshore advection. The inert dual tracers sulfur hexafluoride and helium-3 labelled a freshly upwelled patch of water that was mapped for 8 days. Changes in biological, physical, and chemical characteristics were measured, including phytoplankton productivity, nitrogen assimilation, and regeneration. Freshly upwelled water contained high nutrient concentrations but was depleted in N compared to Redfield stoichiometry. The highest rate of primary productivity was measured on the continental shelf, associated with high rates of nitrogen assimilation and a phytoplankton community dominated by diatoms and flagellates. Indicators of phytoplankton abundance and activity decreased as the labelled water mass transited the continental shelf slope into deeper water, possibly linked to the mixed layer depth exceeding the light penetration depth. By the end of the study, the primary productivity rate decreased and was associated with lower rates of nitrogen assimilation and lower nutrient concentrations. Nitrogen regeneration and assimilation took place simultaneously. Results highlighted the importance of regenerated NH + 4 in sustaining phytoplankton productivity and indicate that the upwelled NO − 3 pool contained an increasing fraction of regenerated NO − 3 as it advected offshore. By calculating this fraction and incorporating it into an f ratio formulation, we estimated that of the 12.38 Tg C of annual regional production, 4.73 Tg C was exportable.

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Section: R Clark Et Al: the Significance Of Nitrogen Regeneratiomentioning

confidence: 99%

The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

2016

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“…Estuaries receive, via river discharge, dissolved and particulate organic and inorganic inputs that provide nitrogen and hold specific bacterial species. Spatial fluctuations of estuarine nitrification have been demonstrated through changes in the distribution and concentration of the different forms of inorganic nitrogen (Berounsky & Nixon 1990, Bronk & Glibert 1993, Pakulski et al 1995. Nitrification rates have also been measured along the plume salinity gradient in several estuaries (Elkins et al 1981, Helder & d e Vries 1983, Owens 1986, Feliatra & Bianchi 1993.…”

Section: Introductionmentioning

confidence: 99%

Regulation of nitrification in the land-ocean contact area of the Rhône River plume (NW Mediterranean)

Bianchi¹,

Feliatra²,

Lefèvre³

1999

Aquat. Microb. Ecol.

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ABSTRACT. The study of natural conditions controhng nitrification processes was undertaken in the estuarine area of the RhBne River (NW Mediterranean Sea) over an annual cycle. Nitrification rates (Noxidation rates, CO2 fixation rates, specific counts of ammonium and nitrite oxidisers) as well as environmental parameters (temperature, salinity, suspended matter, inorganic nitrogen) were measured monthly over a 1 yr period. Depth profiles were obtained in low salinity plume water, at the edge of the plume (intermediate salinity) and in the sea, to study the evolution of nitrification processes from the mouth of the river to the sea of both the brackish surface layer and the bottom nepheloid layer. Nitrification rates in the surface plume generally declined with distance from the river and with increasing salinity, whereas nitrification rates in the benthic nepheloid layer exhibited little spatial variation. This was illustrated by high variability of activities in the plume (50 + 37 and 33 * 21 nM N oxidised h-' for ammonium and nitrite oxidation rates respectively) versus lower variability in the benthlc nepheloid layer (30 * 8 and 22 -c 6 nM N oxidised h-' for ammonium and nitrite oxidation rates respectively). Nitrification rates in both the plume and benthic nepheloid layer were higher in the summer (142 to 175 nM N oxidised h-' for ammonium oxidation and 64 to 96 nM N oxidised h-' for nitrite oxidation) than during the winter months (5 to 30 nM N oxidised h-' for both activities). Highest N-oxidation rates were related to low salinity in the surface layer, corresponding to the highest concentrations of ammonium from the river water. Ammonium oxidation (AO) is regulated by in situ ammonium concentration (r2 = 0.741, p = 0.0001, n = 132) and nitrite oxidation (NO) by the ammonium oxidation rate (r2 = 0.850, p = 0.0001, n = 132). A 0 rate = 14.5 + 10 [NH,'] and NO rate = 4.7 + 0.56 A 0 rate. Qlo values were calculated for ammonium oxidation (2.72) and nitrite oxidation (3.08) rates. The counts of nitrifiers reached 106 cell dm-3, representing less than 2 % of the total bacterial counts. Nitrogen oxidation rates were correlated to nitrifying cell abundances (r = 0.89 to 0.99), and the activities per cell ranged from 1.2 to 1.9 X 10-" m01 N oxidised cell-' d-'. The biomass production of the ammonium oxidisers was demonstrated by the decrease of N oxidised/C fixed ratio from 15.8 in winter to 10.8 in summer, in spite of the increase of A 0 rate in summer. A seasonal fluctuation of N oxidised/C fixed ratio for nitrite oxidisers was not demonstrated; however, the ratio increased from 21.8 * 4.4 in winter to 29.3 * 2.9 in summer. We estimated that 10% (winter) and 20% (summer) of ammonium was nitrified at the mouth of the river. During summer, nitnfication is supported by the flux of ammoni.um from in situ mineralisation and contributes to nitrate excess in the plume. The contribution of nitrification to the N requirement of the primary producers was estimated to be 14 % at the edge of the plume (intermediate salinit...

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“…In the mesohaline Chesapeake Bay, DON turnover times ranged from 0.27 to 2.53 d using 15 N tracer techniques (Bronk et al 1998). In the Choptank River, another subestuary of the Chesapeake Bay, low molecular weight DON had shorter turnover times (15.9 d) than high molecular weight DON (33.8 d;Bronk & Glibert 1993). In the Chesapeake Bay plume, Fuhrman (1990) measured very rapid turnover times using 3 H-DFAA.…”

Section: Extracellular Enzymatic Activitymentioning

confidence: 99%

Extracellular enzyme activity and uptake of carbon and nitrogen along an estuarine salinity and nutrient gradient

Mulholland¹,

Lee²,

Glibert³

2003

Mar. Ecol. Prog. Ser.

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Amino acid oxidation (AAO) and peptide hydrolysis (PH) are processes affecting the recycling of organic material and nutrients. We compared extracellular AAO and PH rates to C and N uptake rates along estuarine gradients of salinity, nutrients and productivity in the Pocomoke River, a subestuary of the Chesapeake Bay. This estuary is seasonally depleted in inorganic N, and rich in dissolved organic material (DOM) throughout the year. AAO, PH, and N uptake rates measured in 1999 and 2000 were not limited to particular size fractions measured, or to auto-or heterotrophic groups of organisms. At a station near the turbidity maximum, where chlorophyll a biomass was highest, smaller (<1.2 µm) size-fractions contributed < 20% of the AAO in May and up to 80% in August when AAO rates were ~10 times lower. Most PH was in the larger (>1.2 µm) size-fraction, except at the least saline station in August of both years. Rates of AAO and PH were not linearly correlated with each other seasonally or spatially. Uptake of NH 4 + dominated total N uptake (> 50%) at all but the freshwater station, although uptake of organic compounds was measurable at all sites. Rates of dissolved free amino acid uptake, measured using dually labeled compounds, were substantial (up to 11% of the total N uptake) and contributed both C and N for growth. Dual labels unambiguously demonstrated that uptake rates of amino acid C and N were uncoupled; amino acid N was taken up preferentially to amino acid C even when rates were corrected for N uptake from AAO. Conceptual models of DOM cycling should include the realization that enzymatic processes and uptake of DOM occur in both 'microbial' and larger size fractions. Thus, competition between bacteria and phytoplankton mixotrophs may be an important factor determining the relative uptake of C and N from amino acids and other organic substrates.KEY WORDS: Amino acid oxidation · Peptide hydrolysis · DOM cycling · N uptake · C uptake Resale or republication not permitted without written consent of the publisher

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Contrasting patterns of dissolved organic nitrogen release by two size fractions of estuarine plankton during a period of rapid NH/ consumption and N02-production

Cited by 50 publications

References 25 publications

The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

The significance of nitrogen regeneration for new production within a filament of the Mauritanian upwelling system

Regulation of nitrification in the land-ocean contact area of the Rhône River plume (NW Mediterranean)

Extracellular enzyme activity and uptake of carbon and nitrogen along an estuarine salinity and nutrient gradient

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