Seawater Dissolved Organic Matter Research Articles

Effect of dissolved organic matter (DOM) of contrasting origins on Cu and Pb speciation and toxicity to Paracentrotus lividus larvae

Water samples of contrasting origin, including natural seawater, two sediment elutriates and sewage-influenced seawater, were collected and obtained to examine the effect of the dissolved organic matter (DOM) present on metal bioavailability. The carbon content (DOC) and the optical properties (absorbance and fluorescence) of the coloured DOM fraction (CDOM) of these materials were determined. Cu and Pb complexation properties were measured by anodic stripping voltammetry (ASV) and the effect of DOM on Cu and Pb bioavailability was studied by means of the Paracentrotus lividus embryo-larval bioassay. Sediment elutriates and sewage-influenced water (1) were enriched 1.4–1.7 times in DOC; (2) absorbed and reemitted more light; and (3) presented higher Cu complexation capacities ( L Cu) than the natural seawater used for their preparation. L Cu varied from 0.08 μM in natural seawater to 0.3 and 0.5 μM in sediment elutriates and sewage-influenced water, respectively. Differences in DOC, CDOM and Cu complexation capacities were reflected in Cu toxicity. DOM enriched samples presented a Cu EC 50 of 0.64 μM, significantly higher than the Cu EC 50 of natural and artificial seawater, which was 0.38 μM. The protecting effect of DOM on Cu toxicity greatly disappeared when the samples were irradiated with high intensity UV-light. Cu toxicity could be successfully predicted considering ASV-labile Cu concentrations in the samples. Pb complexation by DOM was only detected in the DOM-enriched samples and caused little effect on Pb EC 50. This effect was contrary for both elutriates: one elutriate reduced Pb toxicity in comparison with the control artificial seawater, while the other increased it. UV irradiation of the samples caused a marked increase in Pb toxicity, which correlated with the remaining DOC concentration. DOM parameters were related to Cu speciation and toxicity: good correlations were found between DOC and Cu EC 50, while L Cu correlated better with the fluorescence of marine humic substances. The present results stress the importance of characterizing not only the amount but also the quality of seawater DOM to better predict ecological effects from total metal concentration data.

Release of reactive bromine and iodine from diatoms and its possible role in halogen transfer in polar and tropical oceans

An in situ incubation assay measuring the bromination and iodination of phenol red was developed to detect the release of reactive bromine and iodine (primarily hypobromous acid [HOBr] and hypoiodous acid [HOI], respectively) from a putative extracellular bromoperoxidase of marine diatoms. Six of 11 species showed significant release compared to controls. Polar species were particularly active, releasing 0.6–180 fmol HOBr cell−1 h−1 (0.04–1.8 µmol HOBr [mg total chlorophyll]−1 h−1; at the seawater bromide concentration, 840 µmol L−1) and 1.9–271 fmol HOI cell−1 h−1 (0.02–2.7 µmol HOI [mg total chlorophyll]21 h−1, at 100 µmol L−1 iodide). Porosira glacialis consistently showed the highest rates of release. Several temperate diatoms, including Achnanthes cf longipes, known to have a bromide‐sensitive peroxidase involved in stalk formation, and warmwater species also showed the ability to release reactive bromine and iodine. This release was influenced by light, temperature, bromide (and iodide) concentration, H2O2 concentration, and pH. The rate of HOBr release by polar diatoms was much greater than bromoform emissions measured by others from laboratory cultures and seaice algae in the field. This indicates that most of the HOBr released may react with dissolved organic matter (DOM) to form nonvolatile bromine organics. Some fraction of diatom‐produced HOBr and HOI may also form volatile Br2 and I2, which could transfer to the polar troposphere. The reaction of diatom‐released reactive bromine and iodine with seawater DOM may represent the major mechanism in the formation of oceanic polybromo‐ and polyiodo‐methanes.

Molecular Characterisation of Dissolved Organic Matter (DOM) in Groundwaters from the Äspö Underground Research Laboratory, Sweden: A Novel “Finger Printing Tool for Palaeohydrological Assessment

AbstractThe molecular signature of dissolved organic matter (DOM) in groundwaters can be used as a tool when investigating the palaeohydrological response of groundwater systems in relation to changes in recharge environment, and also for examining groundwater compartmentalisation, mixing and transport at underground repositories for radioactive waste. The DOM in groundwaters from two compartmentalised bodies of groundwater of distinctly different origin within the Äspö Underground Research Laboratory (URL), Sweden and in Baltic seawater has been isolated using tangential flow ultrafiltration (TUF) and diafiltration. Recoveries of DOM ranged from 34.7 to 0.1 mg/L with substantial differences in the concentrations of the groundwaters collected only 120 m apart. Analysis by infrared spectroscopy (IR) and pyrolysisgas chromatography-mass spectrometry (Py-GC-MS) of the isolated DOM revealed that the groundwaters contained abundant alkylphenols which may represent heavily decomposed proteins or lignins originating from biopolymers contained within soils. The difference in the distribution and relative abundance of major pyrolysis products groups such as alkyphenols confirmed that the groundwater and Baltic seawater DOM samples were chemically distinct indicating minimal infiltration of marine groundwater derived by recharge from the Baltic or earlier Littorina Sea within the two compartmentalised groundwater bodies.

Structure Elucidation and Characterization of Polychlorinated Biphenyl Carboxylic Acids as Major Constituents of Chromophoric Dissolved Organic Matter in Seawater

Chromophoric or colored dissolved organic matter (CDOM) is one of the principal light adsorbing components of seawater, particularly in the ultraviolet, where it attenuates over 90% of downwelling ultraviolet radiation. In highly productive coastal regions and throughout most of the global ocean, in situ biological production is the major source of CDOM. However, little is known about CDOM composition on the molecular level, and there are only a few reports that link CDOM composition to autochthonous biological sources. Here we report the isolation and characterization of CDOM components from one coastal and two open-ocean sites. Each sample contains a complex mixture of light absorbing (300-400 nm) components, including 2,4-dichlorobenzoic acid and a suite of novel, polychlorinated biphenyl carboxylic acids that closely resemble polychlorinated biphenyls (PCBs) of anthropogenic origin. However, the global inventory and isomer distribution of dissolved chlorinated aromatic acids suggest they are derived from in situ biological production rather than anthropogenic contaminants. These novel chlorinated aromatic acids account for a significant amount of CDOM adsorption in the ultraviolet.

Degradation of riverine dissolved organic matter by seawater bacteria

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 37:9-22 (2004) - doi:10.3354/ame037009 Degradation of riverine dissolved organic matter by seawater bacteria Emma J. Rochelle-Newall1,3,*, Marie-Dominique Pizay1, Jack J. Middelburg2, Henricus T. S. Boschker2, Jean-Pierre Gattuso1 1Observatoire Océanologique, Laboratoire d’Océanographie de Villefranche, CNRS-UPMC, 06234 Villefranche-sur-Mer Cedex, France2Netherlands Institute of Ecology (NIOO-KNAW), PO Box 140, 4400AC, Yerseke, The Netherlands3Present address: Centre IRD Noumea, BP A5, Noumea, New Caledonia *Email: emma.rochelle-newall@noumea.ird.nc ABSTRACT: The functional response of a seawater bacterial community transplanted into freshwater dissolved organic matter (DOM) was investigated together with the response of natural populations of bacteria to size-fractioned natural source water. Seawater bacteria were incubated over a period of 8 d in size-fractionated, freshwater DOM collected from Randers Fjord, Denmark, during spring (April) and summer (August) of 2001. Three fractions were used: 0.2 µm filtered (<0.2 µm-DOM), >1 kDa (high molecular weight, HMW-DOM) and <1 kDa (low molecular weight, LMW-DOM). The results were compared with parallel control incubations of freshwater bacteria in size-fractionated freshwater DOM and seawater bacteria in size-fractionated seawater DOM. There were few differences in bacterial abundance (BA) and production (BP) within each incubation type in spring, but this was not the case in summer. While the seawater bacteria transplanted into freshwater HMW-DOM performed similarly to those in seawater HMW-DOM, freshwater bacteria in freshwater HMW-DOM exhibited higher BA, BP and bacterial respiration (BR), indicating a difference in the physiological abilities of the seawater bacterial assemblage compared to that of the natural freshwater assemblage. Bacterial growth efficiency (BGE) varied between 11 and 41% and the highest values were generally in the HMW-DOM size fraction. Comparison of the ‘bioavailability’ of the DOM predicted from BGE, the amino acid degradation index (DI), dissolved organic carbon degradation rates and the bioavailability index showed that net change in DI of dissolved combined amino acids over the course of an incubation can be a good predictor of most of the other indices. The separation of DOM into molecular weight size fractions resulted in different estimates of bioavailability than would have been predicted from the rates observed in the <0.2 µm-DOM fraction. These results further demonstrate the flexibility of bacteria in their ability to utilize different sources of DOM, and highlight the variability that can be observed when different indices are used to determine the bioavailability of organic matter to heterotrophic bacteria. KEY WORDS: Bacterial growth efficiency · BGE · HMW · LMW · DOM · Randers Fjord Estuary · Amino acids · Degradation Index · DI Full article in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 37, No. 1. Online publication date: November 02, 2004 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2004 Inter-Research.

Transport and diagenesis of dissolved and particulate terrigenous organic matter in the North Pacific Ocean

Lignin measurements were made on suspended particulate organic matter (POM), total dissolved organic matter (DOM), high-molecular-weight (HMW) DOM, and low-molecular-weight (LMW) DOM in the North Pacific at Station Aloha. Carbon-normalized yields of lignin and δ 13C measurements indicate that while terrigenous organic matter accounts only for ∼1% of DOM in seawater, submicron POM has a substantial terrigenous component. The apparent size distribution and terrigenous nature of the particles is consistent with an aerosol source, but these particles could also be delivered to the ocean via rivers. Ratios of syringyl to vanillyl phenols as well as the fraction of dissolved lignin in HMW DOM provide molecular evidence of photochemical oxidation. Several differences in lignin composition and concentrations were evident between water masses. In particular, concentrations in North Pacific Intermediate Water were a factor of two greater than at all other depths. This is likely a reflection of higher riverine input via the Sea of Okhotsk. These trends suggest that lignin could serve as a general circulation tracer in addition to tracing riverine input and diagenetic processing of terrigenous organic matter in the ocean.

A comparison of the chemical characteristics of oceanic DOM and extracellular DOM produced by marine algae

The chemical characteristics of extracellular high molecular weight (HMW) dissolved organic matter (DOM) from 3 species of marine phytoplankton were compared to HMW DOM in seawater. Thalassiosira weissflogii, Emiliania huxleyi and Phaeocystis sp., were grown in nutrient enriched seawater that had been previously ultrafiltered to remove HMW DOM. The extracellular HMW DOM produced in these cultures was isolated by ultrafiltration and characterized using nuclear magnetic resonance (NMR) spectroscopy, and molecular level analyses. All species exude DOM rich in polysaccharides, and the exudates of T. weissflogii and E. huxleyi closely resemble acyl heteropolysaccharides (APS) previously identified as major constituents of naturally occurring marine HMW DOM. Degradation of the T. weissflogii exudate alters the chemical composition of the DOM, which we attribute to differences in the reactivity of specific polysaccharides. The component within the exudate that most resembles seawater DOM has a slower degradation rate relative to the total polysaccharide fraction. Our study indicates that APS isolated from the surface ocean can have a direct algal source and that APS may accumulate in seawater as a result of its metabolic resistance.

Characterization of marine and terrestrial DOM in seawater using excitation-emission matrix spectroscopy

Abstract High-resolution fluorescence spectroscopy was used to characterize dissolved organic matter (DOM) in concentrated and unconcentrated water samples from a wide variety of freshwater, coastal and marine environments. Several types of fluorescent signals were observed, including humic-like, tyrosine-like, and tryptophan-like. Humic-like fluorescence consisted of two peaks, one stimulated by UV excitation (peak A) and one by visible excitation (peak C). For all samples, the positions of both excitation and emission maxima for peak C were dependent upon wavelength of observation, with a shift towards longer wavelength emission maximum at longer excitation wavelength and longer wavelength excitation maximum at longer emission wavelength. A trend was observed in the position of wavelength-independent maximum fluorescence ( Ex max Em max ) for peak C, with maximum at shorter excitation and emission wavelengths for marine samples than for freshwater samples. Mean positions of these maxima were: rivers Ex max Em max = 340 448 nm; coastal water Ex max Em max = 342 442 nm; marine shallow transitional Ex max Em max = 310 423 nm; marine shallow eutrophic Ex max Em max = 299 389 nm; and marine deep Ex max Em max = 340 438 nm. Differences suggest that the humic material in marine surface waters is chemically different from humic material in the other environments sampled. These results explain previous conflicting reports regarding fluorescence properties of DOM from natural waters and also provide a means of distinguishing between water mass sources in the ocean.

Isolation of Marine Dissolved Organic Matter: Evaluation of Sequential Combinations of XAD Resins 2, 4, and 7

The sorptive behavior of resins XAD2, -4, and -7 for dissolved organic carbon (DOC) derived from marine phytoplankton was compared. The resins were arranged in varying sequences, which proved to be critical for determining the efficiency of DOC isolation. The sequence XAD7/2/4 allowed the isolation of a very high percentage of DOC (65%) from the seawater matrix. A mixed bed of the same resins showed a significantly lower recovery (39%). Varying amounts of the material adsorbed by the individual resins could not be recovered by NaOH/methanol elution. The percentage of DOC firmly retained by each resin was 32, 21, and 2% in XAD2, XAD4, and XAD7, respectively. Characterizing the nature of dissolved organic matter (DOM) in seawater by direct analysis typically accounts for less than 1 %of the total.' Alternatively, DOM can be isolated from seawater, thereby providing, improved analytical conditions in regard to ionic strength and concentration levels. Various methods have been employed to isolate DOM: the adsorption of DOM from acidified seawater onto XAD resins has proved to be useful, even though these are selective for mainly hydrophobic compounds. Some workers use a combination of XAD and ion-exchange resins to recover the hydrophilic fraction of DOM and, hence, achieved almost 100% recovery of dissolved organic carbon (DOC).Z Unfortunately this methodology is not appropriate for high-salinity matrices such as seawater. Tangential-flow ultrafiltration through 1000-Da cutoff filters only recovers approximately 30% of DOM in seawater.' Currently there is much speculation about the amount and form of DOM in the world's oceans. However, our understanding of the generation of this pool, its transformation by the trophic network, and the humification of organic matter in the water column is hindered by these technical difficulties. Lara and Thomas3 presented results from a study following the humification of DOC recently produced by laboratory diatom cultures. It was found that ca. 30% of the material adsorbed by the XAD2 resin used for DOC fractionation could not be recovered by standard NaOH/methanol elution. In an attempt to separate and operationally delimit the nature of this tightly bound DOM fraction, we subsequently compared the sorptive behavior of three different XAD resins arranged in varying sequences. Our main research is orientated toward nitrogenous compounds and organic acids in the humification (1) Bcnner, R.; Pakulski, J. D.; McCarthy, M.; Hedges, J. I.; Hatchet, P. G.

Photoproduction and Quenching of Hydrated Electrons from Dissolved Organic Matter in Natural Waters

Abstract Laser photolysis was used to investigate the production and quenching of hydrated electrons formed after absorption of 355 nm light by dissolved organic matter (DOM) in natural waters. Correlation between the hydrated electrons generated and dissolved organic carbon in seawaters was found. The DOM in land waters ejected more hydrated electrons than seawater DOM did. Land waters contained much natural fluorescent organic matter, so the DOM in the land waters was rich in photochemically sensitive chromophores. Quenching of the hydrated electrons by the inorganic ions, nitrite, nitrate, Cd2+, Ni2+, Co2+, and [Co(NH3)6]3+ were investigated by a first-order function and the Stern–Volmer model. With the former, the quenching rate constants were 10−9 to 10−10 dm3 mol−1 s−1, which was close to reported values. No regional differences were found among the seawater samples. This result suggested similar quenching mechanisms for hydrated electrons generated in the different seawaters. With the Stern–Volmer model, primary quenching was estimated. Quenching studies of land waters suggested that DOM had an aggregate nature in such waters.

Aminopeptidase Activity in Marine Chroococcoid Cyanobacteria

Synechococci are important primary producers in the ocean and can also utilize some components of the dissolved organic matter (DOM). The readily utilizable DOM in seawater is mainly polymeric (e.g., protein, polysaccharide) or phosphorylated and requires hydrolysis prior to uptake. We examined whether synechococci express ectoenzymes to hydrolyze DOM components and considered the possible significance of ectohydrolases for Synechococcus ecology and organic matter cycling in the sea. Five strains of non-nitrogen-fixing synechococci in axenic cultures were tested for enzyme activities with fluorogenic substrates. All strains show ectocellular aminopeptidase activity, but other enzymes were undetectable. The aminopeptidase level was in the range determined for five marine heterotrophic bacterial isolates tested for comparison. Aminopeptidase was not secreted into the medium; the majority (74%; tested in WH 7803) was cell surface bound, and a small fraction was periplasmic. The periplasmic activity was not released by cold osmotic shock of WH 7803. Phenylmethylsulfonyl fluoride and EDTA, inhibitors of serine and metalloproteases, strongly or completely inhibited WH 7803 aminopeptidase. The enzyme seemed constitutive; per-cell activity did not change during incubations in unenriched seawater, bovine serum albumin, or nitrate-replete mineral medium. In natural planktonic assemblages in the Southern California Bight, aminopeptidase activity was correlated with Synechococcus abundance as well as the abundance of other bacteria. Ectocellular aminopeptidase may be common in marine synechococci and play roles in their nitrogen nutrition, particularly in low-nitrate and low-light environments. Since synechococci are much less abundant than heterotrophic bacteria in seawater, the impact of Synechococcus aminopeptidase on proteolysis in the sea is likely to be episodic and restricted to specialized microenvironments.

Bulk Chemical Characteristics of Dissolved Organic Matter in the Ocean

Dissolved organic matter (DOM) is the largest reservoir of reduced carbon in the oceans. The nature of DOM is poorly understood, in part, because it has been difficult to isolate sufficient amounts of representative material for analysis. Tangential-flow ultrafiltration was shown to recover milligram amounts of >1000 daltons of DOM from seawater collected at three depths in the North Pacific Ocean. These isolates represented 22 to 33 percent of the total DOM and included essentially all colloidal material. The elemental, carbohydrate, and carbon-type (by (13)C nuclear magnetic resonance) compositions of the isolates indicated that the relative abundance of polysaccharides was high ( approximately 50 percent) in surface water and decreased to approximately 25 percent in deeper samples. Polysaccharides thus appear to be more abundant and reactive components of seawater DOM than has been recognized.

Dissolved ATP in the sea and its utilisation by marine bacteria.

THE biologically labile fraction of the dissolved organic matter (DOM) in the oceans seems to be a chemically complex solution of a wide variety of compounds derived mainly from the contents of cellular metabolic pools released into the seawater after the death and cell lysis of marine organisms. This fraction is of particular geochemical interest because of its importance in understanding the cycling of organic matter in the marine environment. Because of methodological problems arising from the extremely low concentrations of individual compounds, compound-specific analyses have been limited to only a few components of the DOM, such as ammo acids1, lipids2, sugars5, and vitamins3. Adenosine-5′-triphosphate (ATP) would be a useful tracer for following the production and fate of labile DOM in seawater as it is a universal component of the cellular metabolic pools of all living organisms. We report here that dissolved ATP (DATP) occurs in seawater in significant concentrations (0.1–0.6 µg 1−1) and is utilised rapidly by marine bacteria.