scholarly journals Oxygen utilization and downward carbon flux in an oxygen-depleted eddy in the eastern tropical North Atlantic

2016 ◽  
Vol 13 (19) ◽  
pp. 5633-5647 ◽  
Author(s):  
Björn Fiedler ◽  
Damian S. Grundle ◽  
Florian Schütte ◽  
Johannes Karstensen ◽  
Carolin R. Löscher ◽  
...  
Keyword(s):  
Organic Matter ◽  
North Atlantic ◽  
Utilization Rate ◽  
Surface Mixed Layer ◽  
Oxygen Utilization ◽  
Near Surface ◽  
Underwater Gliders ◽  
Tropical North Atlantic ◽  
Order Of Magnitude ◽  
Oxygen Utilization Rate

Abstract. The occurrence of mesoscale eddies that develop suboxic environments at shallow depth (about 40–100 m) has recently been reported for the eastern tropical North Atlantic (ETNA). Their hydrographic structure suggests that the water mass inside the eddy is well isolated from ambient waters supporting the development of severe near-surface oxygen deficits. So far, hydrographic and biogeochemical characterization of these eddies was limited to a few autonomous surveys, with the use of moorings, underwater gliders and profiling floats. In this study we present results from the first dedicated biogeochemical survey of one of these eddies conducted in March 2014 near the Cape Verde Ocean Observatory (CVOO). During the survey the eddy core showed oxygen concentrations as low as 5 µmol kg−1 with a pH of around 7.6 at approximately 100 m depth. Correspondingly, the aragonite saturation level dropped to 1 at the same depth, thereby creating unfavorable conditions for calcifying organisms. To our knowledge, such enhanced acidity within near-surface waters has never been reported before for the open Atlantic Ocean. Vertical distributions of particulate organic matter and dissolved organic matter (POM and DOM), generally showed elevated concentrations in the surface mixed layer (0–70 m), with DOM also accumulating beneath the oxygen minimum. With the use of reference data from the upwelling region where these eddies are formed, the oxygen utilization rate was calculated by determining oxygen consumption through the remineralization of organic matter. Inside the core, we found these rates were almost 1 order of magnitude higher (apparent oxygen utilization rate (aOUR); 0.26 µmol kg−1 day−1) than typical values for the open North Atlantic. Computed downward fluxes for particulate organic carbon (POC), were around 0.19 to 0.23 g C m−2 day−1 at 100 m depth, clearly exceeding fluxes typical for an oligotrophic open-ocean setting. The observations support the view that the oxygen-depleted eddies can be viewed as isolated, westwards propagating upwelling systems of their own, thereby represent re-occurring alien biogeochemical environments in the ETNA.

scholarly journals Oxygen Utilization and Downward Carbon Flux in an Oxygen-Depleted Eddy in the Eastern Tropical North Atlantic

2016 ◽  
Author(s):  
B. Fiedler ◽  
D. Grundle ◽  
F. Schütte ◽  
J. Karstensen ◽  
C. R. Löscher ◽  
...  
Keyword(s):  
Organic Matter ◽  
North Atlantic ◽  
Lower Boundary ◽  
Euphotic Zone ◽  
Shallow Depth ◽  
Surface Mixed Layer ◽  
Low Oxygen ◽  
Oxygen Utilization ◽  
Near Surface ◽  
Tropical North Atlantic

Abstract. The occurrence of mesoscale eddies that develop an extreme low oxygen environment at shallow depth (about 40 to 100 m) has recently been reported for the eastern tropical North Atlantic (ETNA). Their hydrographic structure suggests that the water mass inside the eddy is well isolated from ambient waters supporting the development of severe near-surface oxygen deficits. So far, hydrographic and biogeochemical characterization of these eddies was limited to a few autonomous surveys, using moorings, underwater gliders and profiling floats. In this study we present results from the first dedicated biogeochemical survey of one of these eddies conducted in March 2014 near the Cape Verde Ocean Observatory (CVOO). At the time of the survey the eddy core showed lowest oxygen concentrations of less than 5 μmol kg−1 and a pH of approx. 7.6 at the lower boundary of the euphotic zone. Correspondingly, the aragonite saturation level dropped to 1 thereby creating unfavorable conditions for calcifying organisms at this shallow depth. To our knowledge, such enhanced acidity within near-surface waters has never been reported before for the open Atlantic Ocean. Vertical distributions of particulate and dissolved organic matter (POM, DOM) generally show elevated concentrations in the surface mixed layer, but particularly DOM also accumulates beneath the oxygen minimum. Considering reference data from the upwelling region where these eddies are formed, we determined the oxygen consumption through remineralization of organic matter and found an enhancement of apparent oxygen utilization rates (aOUR, 0.26 μmol kg−1 d−1) by almost one order of magnitude when compared with typical values for the open North Atlantic. Computed downward fluxes for particulate organic carbon (POC) at 100 m were about 0.19 to 0.23 g C m−2 d−1 which clearly exceed fluxes typical for an oligotrophic open ocean setting. The observations support the view that the oxygen depleted eddies can be viewed as isolated, westwards propagating upwelling systems as their own.

An assessment of sewage sludge stability with a specific oxygen utilization rate (SOUR) test method

2000 ◽  
Vol 42 (9) ◽  
pp. 37-40 ◽  
Author(s):  
K. A. Samson ◽  
G. A. Ekama
Keyword(s):  
Organic Matter ◽  
Sewage Sludge ◽  
Test Method ◽  
Utilization Rate ◽  
Oxygen Utilization ◽  
Sewage Sludges ◽  
Indirect Measure ◽  
Oxygen Utilization Rate ◽  
Specific Oxygen Utilization Rate ◽  
Biodegradable Organic Matter

Sewage sludge treatment systems are intended to stabilize the sludge so that its disposal or reuse can be environmentally acceptable. However, stabilized sludges may still contain residual biodegradable organic matter that can be environmentally a nuisance. This paper presents a specific oxygen utilization rate [SOUR, mgO2/(gVSS·h)] batch reactor test method to quantify the residual biodegradable organic matter content of the treated (stabilized) sewage sludges. The results of the study, in which 37 SOUR batch tests were done on 10 different sewage sludges, show that the SOUR, when determined over a prolonged period (4 to 5 days), gives an indirect measure of sludge stability defined as the % soluble and particulate residual biodegradable organics in the sludge; to determine % sludge stability, it is necessary to simulate the experimental SOUR data by means of a general activated sludge model. The % sludge stability obtained for the 10 different sludges, taking due account of their soluble and particulate constituents, was consistent with that expected from the stabilization treatment systems to which the sludges were subjected.

Sulfide production and wastewater quality – investigations in a pilot plant pressure sewer

2001 ◽  
Vol 43 (5) ◽  
pp. 129-136 ◽  
Author(s):  
N. Tanaka ◽  
T. Hvitved-Jacobsen
Keyword(s):  
Organic Matter ◽  
Pilot Plant ◽  
Quality Parameters ◽  
Utilization Rate ◽  
Oxygen Utilization ◽  
Sulfide Production ◽  
Wastewater Quality ◽  
Inner Diameter ◽  
Oxygen Utilization Rate ◽  
The Relationship

The relationship linking sulfide production rate and wastewater quality in terms of its biodegradability was studied using a pilot plant pressure sewer (inner diameter: 102 mm, length: 47 m). Furthermore, anaerobic transformations of wastewater organic matter were investigated. Wastewater characterization based on oxygen utilization rate (OUR) measurements and VFA analyses was employed. As wastewater quality parameters essential for the sulfide production, COD components and dissolved carbohydrate were focused on. Readily biodegradable substrate and fermentable, readily biodegradable substrate were better parameters than traditional dissolved COD for the prediction of sulfide production rates in a pressure sewer. From the results obtained, it was possible to integrate the sulfide production process with the transformation processes of wastewater organic matter in pressure sewers.

scholarly journals Particle export fluxes to the oxygen minimum zone of the eastern tropical North Atlantic

2017 ◽  
Vol 14 (7) ◽  
pp. 1825-1838 ◽  
Author(s):  
Anja Engel ◽  
Hannes Wagner ◽  
Frédéric A. C. Le Moigne ◽  
Samuel T. Wilson
Keyword(s):  
Organic Matter ◽  
North Atlantic ◽  
Organic Phosphorus ◽  
Euphotic Zone ◽  
Carbon Export ◽  
Organic Matter Quality ◽  
B Values ◽  
Chl A ◽  
Tropical North Atlantic ◽  
Particle Export

Abstract. In the ocean, sinking of particulate organic matter (POM) drives carbon export from the euphotic zone and supplies nutrition to mesopelagic communities, the feeding and degradation activities of which in turn lead to export flux attenuation. Oxygen (O2) minimum zones (OMZs) with suboxic water layers (< 5 µmol O2 kg−1) show a lower carbon flux attenuation compared to well-oxygenated waters (> 100 µmol O2 kg−1), supposedly due to reduced heterotrophic activity. This study focuses on sinking particle fluxes through hypoxic mesopelagic waters (< 60 µmol O2 kg−1); these represent  ∼  100 times more ocean volume globally compared to suboxic waters, but they have less been studied. Particle export fluxes and attenuation coefficients were determined in the eastern tropical North Atlantic (ETNA) using two surface-tethered drifting sediment trap arrays with seven trapping depths located between 100 and 600 m. Data on particulate matter fluxes were fitted to the normalized power function Fz =  F100 (z∕100)−b, with F100 being the flux at a depth (z) of 100 m and b being the attenuation coefficient. Higher b values suggest stronger flux attenuation and are influenced by factors such as faster degradation at higher temperatures. In this study, b values of organic carbon fluxes varied between 0.74 and 0.80 and were in the intermediate range of previous reports, but lower than expected from seawater temperatures within the upper 500 m. During this study, highest b values were determined for fluxes of particulate hydrolyzable amino acids (PHAA), followed by particulate organic phosphorus (POP), nitrogen (PN), carbon (POC), chlorophyll a (Chl a) and transparent exopolymer particles (TEP), pointing to a sequential degradation of organic matter components during sinking. Our study suggests that in addition to O2 concentration, organic matter composition co-determines transfer efficiency through the mesopelagic. The magnitude of future carbon export fluxes may therefore also depend on how organic matter quality in the surface ocean changes under influence of warming, acidification and enhanced stratification.

Important limitations in the modeling of activated sludge: biased calibration of the hydrolysis process

2002 ◽  
Vol 45 (12) ◽  
pp. 23-36 ◽  
Author(s):  
G. Insel ◽  
Ö. Karahan Gül ◽  
D. Orhon ◽  
P.A. Vanrolleghem ◽  
M. Henze
Keyword(s):  
Activated Sludge ◽  
Hydrolysis Rate ◽  
Utilization Rate ◽  
Oxygen Utilization ◽  
Experimental Assessment ◽  
Experimental Database ◽  
Hydrolysis Process ◽  
Biochemical Mechanisms ◽  
Oxygen Utilization Rate ◽  
Activated Sludge Models

The merit of activated sludge models depends on the accuracy and reliability of the information they contain on the wastewater to be treated and the biochemical mechanisms involved. In most advanced calibration studies, respirometry i.e. the measurement of the oxygen utilization rate, (OUR), provides the majority of the required experimental database. However, currently used procedures still involve a number of basic and practical problems. Model evaluation of the OUR data may generate a distorted image of the processes involved. Hydrolysis is the most important, yet the most vulnerable process as far as the experimental assessment of accurate kinetic parameters is concerned. This study intends to provide an overview of major experimental limitations in the modeling of activated sludge, with emphasis on the appropriate experimental design for the assessment of the hydrolysis rate.

scholarly journals Seismic imaging of a thermohaline staircase in the western tropical North Atlantic

2010 ◽  
Vol 7 (1) ◽  
pp. 361-389
Author(s):  
I. Fer ◽  
P. Nandi ◽  
W. S. Holbrook ◽  
R. W. Schmitt ◽  
P. Páramo
Keyword(s):  
Internal Wave ◽  
North Atlantic ◽  
Vertical Mixing ◽  
Global Ocean ◽  
Turbulent Dissipation ◽  
Tropical North Atlantic ◽  
Seismic Reflection Method ◽  
Order Of Magnitude ◽  
Salt Fingering ◽  
Wave Induced

Abstract. Multichannel seismic data acquired in the Lesser Antilles in the western tropical North Atlantic indicate that the seismic reflection method has imaged an oceanic thermohaline staircase. Synthetic modeling of observed density and sound speed profiles corroborates inferences from the seismic imagery. Laterally coherent, uniform layers are present at depths ranging from 550–700 m and have a separation of ~20 m, with thicknesses increasing with depth. Reflection coefficient, a measure of the acoustic impedance contrasts, associated with the interfaces is one order of magnitude greater than the background levels. Hydrography sampled in previous surveys puts a constraint on the longevity of these layers in this area to within a maximum of three years. Spectral analysis of layer horizons in the thermohaline staircase indicates that internal wave activity is anomalously low, suggesting weak internal wave-induced turbulence and mixing. Results from two independent measurements, the application of a finescale parameterization to observed high-resolution velocity profiles and direct measurements of turbulent dissipation rate, confirm the low levels of turbulence and mixing. The lack of internal wave-induced mixing allows for the maintenance of the staircase. Our observations show the potential that seismic oceanography can contribute to an improved understanding of temporal occurrence rates, and the geographical distribution of thermohaline staircases and can improve current estimates of vertical mixing rates ascribable to salt fingering in the global ocean.

scholarly journals Effects of nitrate and phosphate supply on chromophoric and fluorescent dissolved organic matter in the Eastern Tropical North Atlantic: a mesocosm study

2015 ◽  
Vol 12 (10) ◽  
pp. 7209-7255
Author(s):  
A. N. Loginova ◽  
C. Borchard ◽  
J. Meyer ◽  
H. Hauss ◽  
R. Kiko ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Organic Matter ◽  
Optical Properties ◽  
Amino Acid ◽  
Dissolved Organic Matter ◽  
North Atlantic ◽  
Phytoplankton Biomass ◽  
Open Ocean ◽  
Nutrient Concentrations ◽  
Tropical North Atlantic

Abstract. The Eastern Tropical North Atlantic (ETNA) is an open ocean region with little input of terrestrial dissolved organic matter (DOM), suggesting that pelagic production has to be the main source of DOM. Inorganic nitrogen (DIN) and phosphorus (DIP) concentrations affect pelagic production, leading to DOM modifications. The quantitative and qualitative changes in DOM are often estimated by its optical properties. Colored DOM (CDOM) is often used to estimate dissolved organic carbon (DOC) concentrations by applied techniques, e.g. through remote sensing, whereas DOM properties, such as molecular weight, can be estimated from the slopes of the CDOM absorption spectra (S). Fluorescence properties of CDOM (FDOM) allow discriminating between different structural CDOM properties. The investigation of distribution and cycling of CDOM and FDOM was recognized to be important for understanding of physical and biogeochemical processes, influencing DOM. However, little information is available about effects of nutrient variability on CDOM and FDOM dynamics. Here we present results from two mesocosm experiments conducted with a natural plankton community of the ETNA, where effects of DIP ("Varied P") and DIN ("Varied N") supply on optical properties of DOM were studied. CDOM accumulated proportionally to phytoplankton biomass during the experiments. S decreased over time indicating accumulation of high molecular weight DOM. In Varied N, an additional CDOM portion, as a result of bacterial DOM reworking, was determined. It increased the CDOM fraction in DOC proportionally to the supplied DIN. The humic-like FDOM component (Comp.1) was derived by bacteria proportionally to DIN supply. The bound-to-protein amino acid-like FDOM component (Comp.2) was released irrespectively to phytoplankton biomass, but depending on DIP and DIN concentrations, as a part of an overflow mechanism. Under high DIN supply, Comp.2 was removed by bacterial reworking processes, leading to an accumulation of humic-like Comp.1. No influence of nutrient availability on amino acid-like FDOM component in peptide form (Comp.3) was observed. Comp.3 potentially acted as an intermediate product during formation or degradation Comp.2. Our findings suggest that changes in nutrient concentrations may lead to substantial responses in the quantity and "quality" of optically active DOM and, therefore, might bias results of the applied techniques for an estimation of DOC concentrations in open ocean regions.

scholarly journals Photochemical production of ammonium in the oligotrophic Cyprus Gyre (Eastern Mediterranean)

2006 ◽  
Vol 3 (4) ◽  
pp. 439-449 ◽  
Author(s):  
V. Kitidis ◽  
G. Uher ◽  
R. C. Upstill-Goddard ◽  
R. F. C. Mantoura ◽  
G. Spyres ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Eastern Mediterranean ◽  
Light Attenuation ◽  
Euphotic Zone ◽  
N Deposition ◽  
Surface Mixed Layer ◽  
Atmospheric N Deposition ◽  
New Production ◽  
Order Of Magnitude

Abstract. We investigated the photoproduction of ammonium (NH4+) in surface waters of the Cyprus gyre in the central Eastern Mediterranean in May 2002, in 8 on deck irradiations with freshly collected, filtered samples. NH4+ photoproduction (photoammonification) increased with time-integrated irradiance during the course of irradiations. Photoammonification rates around local noon were 0.4–2.9 nmol L−1 h−1. Normalised to time integrated irradiance, these rates were 0.9–3.8 pmol L−1 h−1/(W m−2) and were significantly correlated with Chromophoric Dissolved Organic Matter (CDOM) absorbance at 300 nm normalised to Dissolved Organic Carbon (DOC). These results are consistent with the notion that successive CDOM photobleaching in the surface mixed layer results in decreased DOC-normalised light absorbance concurrent with decreased dissolved organic matter reactivity with regard to photochemical NH4+ release. Combining our experimental data with estimates of annual solar irradiance and water column light attenuation yields an annual photoammonification rate for the Cyprus Gyre of 40±17 mmol m−2 a−1, equivalent to ~12±5% of the previously estimated annual nitrogen requirement of new production and in the same order of magnitude as atmospheric N deposition in this region. Based on this analysis, NH4+ photoproduction makes a small, but significant contribution to the nitrogen budget of the euphotic zone in the oligotrophic Cyprus Gyre.

scholarly journals N2 Fixation by Unicellular Bacterioplankton from the Atlantic and Pacific Oceans: Phylogeny and In Situ Rates

2004 ◽  
Vol 70 (2) ◽  
pp. 765-770 ◽  
Author(s):  
Luisa I. Falcón ◽  
Edward J. Carpenter ◽  
Frank Cipriano ◽  
Birgitta Bergman ◽  
Douglas G. Capone
Keyword(s):  
North Atlantic ◽  
Surface Waters ◽  
North Pacific ◽  
Marine Cyanobacteria ◽  
Common Ancestry ◽  
Near Surface ◽  
16S Ribosomal Dna ◽  
Tropical North Atlantic ◽  
Night And Day

ABSTRACT N2-fixing proteobacteria (α and γ) and unicellular cyanobacteria are common in both the tropical North Atlantic and Pacific oceans. In near-surface waters proteobacterial nifH transcripts were present during both night and day while unicellular cyanobacterial nifH transcripts were present during the nighttime only, suggesting separation of N2 fixation and photosynthesis by unicellular cyanobacteria. Phylogenetic relationships among unicellular cyanobacteria from both oceans were determined after sequencing of a conserved region of 16S ribosomal DNA (rDNA) of cyanobacteria, and results showed that they clustered together, regardless of the ocean of origin. However, sequencing of nifH transcripts of unicellular cyanobacteria from both oceans showed that they clustered separately. This suggests that unicellular cyanobacteria from the tropical North Atlantic and subtropical North Pacific share a common ancestry (16S rDNA) and that potential unicellular N2 fixers have diverged (nifH). N2 fixation rates for unicellular bacterioplankton (including small cyanobacteria) from both oceans were determined in situ according to the acetylene reduction and 15N2 protocols. The results showed that rates of fixation by bacterioplankton can be almost as high as those of fixation by the colonial N2-fixing marine cyanobacteria Trichodesmium spp. in the tropical North Atlantic but that rates are much lower in the subtropical North Pacific.

Correct manipulation method of MBR operating parameters in membrane fouling studies

2013 ◽  
Vol 68 (10) ◽  
pp. 2301-2308 ◽  
Author(s):  
N. Kayaalp ◽  
C. Kinaci
Keyword(s):  
Retention Time ◽  
Membrane Fouling ◽  
Organic Loading Rate ◽  
Utilization Rate ◽  
Operating Parameters ◽  
Oxygen Utilization ◽  
Membrane Area ◽  
Membrane Flux ◽  
Oxygen Utilization Rate ◽  
Common Application

In this study, various parameter manipulation methods, variable sludge retention time (SRT)–variable mixed liquor suspended solids (MLSS) concentration, constant SRT–variable MLSS concentration and variable SRT–constant MLSS concentration, were compared based on the interrelationships among the following membrane bioreactor operating parameters: SRT, food to microorganisms (biomass) (F/M) ratio, MLSS concentration, volumetric organic loading rate (OLR) and membrane flux. Although it is the most applied method, concurrent change of SRT (or F/M ratio) and MLSS concentration is not a good parameter manipulation method because it causes unnecessary changes in many other parameters such as viscosity, oxygen transfer efficiency and oxygen utilization rate. The method of constant SRT–variable MLSS concentration has similar disadvantages to the method of variable SRT–variable MLSS concentration. The best alternative parameter manipulation method to study membrane fouling is the method of variable SRT–constant MLSS concentration because this method eliminates unnecessary changes in other parameters. In addition, while changing OLR or hydraulic retention time (HRT), contrary to the common application, membrane flux should be kept constant because any change in flux overrides changes in other parameters. Accordingly, required changes in OLR or HRT should be made by adjusting membrane area rather than membrane flux.

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