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  • 1
    Electronic Resource
    Electronic Resource
    Determination of methylmercury in biological samples by semiautomated headspace analysis (1985)
    s.l. : American Chemical Society
    Analytical chemistry 57 (1985), S. 2788-2791 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac00291a011
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  • 2
    Electronic Resource
    Electronic Resource
    Variability in the origin of carbon substrates for bacterial communities in mangrove sediments (2004)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology ecology 49 (2004), S. 0 
    Details
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Organic carbon in mangrove sediments originates from both local sources (mangroves, microphytobenthos) and tidal inputs (e.g. phytoplankton, seagrass-derived material). The relative inputs of these sources may vary strongly, both within and between different mangrove sites. We combined elemental (TOC/TN) and bulk δ13C analysis on sediment cores from various mangrove sites with δ13C data of bacteria-specific phospholipid fatty acids (PLFA) in order to identify the dominant carbon substrates used by in situ bacterial communities. δ13C values of each of these markers showed a range of 10% or more across the different sites and sampling depths, but generally followed the δ13C trend observed in bulk organic carbon. Several sediment cores show a strong vertical gradient in PLFA δ13C, suggesting a selectivity for algal-derived carbon in the surface layers. Our data demonstrate that the origin of bacterial carbon substrates varies widely across different mangrove sites, and imply that data on mineralization of organic matter cannot be directly incorporated in ecosystem carbon budgets without an estimation of the contribution of various sources.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/j.femsec.2004.03.004
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of methylmercury in fish by headspace-gas chromatography with microwave-induced-plasma detection (1991)
    Springer
    Water, air & soil pollution 56 (1991), S. 103-115 
    Details
    ISSN: 1573-2932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Some additional experiments checking out the extraction method recently developed for the determination of MeHg in biological samples by Headspace Gas Chromatography with Microwave Induced Plasma atomic emission spectroscopy detection were performed. In this method, the MeHg is cleaved from the biological tissue by H2SO4 and by addition of iodoacetic acid converted to the iodide form. These reaction steps take place in a closed headspace vial. The H2SO4 concentration and the sample matrix have an important influence on the recovery of the MeHg from the sample and these effects are discussed. The method was then applied to the determination of MeHg in cod fish caught in the North Sea. Levels found ranged from 0.13 to 0.63 μg g−1 dw with a mean of 0.33 μg g−1 on the 25 samples analyzed. The total Hg content of these samples was also determined by Cold Vapour Atomic Absorption Spectrometry, and all data pooled ranged from 0.19 to 0.90 μg g−1 with a mean of 0.40 μg g−1. A study of the ratio MeHg/total Hg revealed that MeHg always constituted more than 60 % of the total Hg level, with a mean of 83 % on the 25 samples. The percentage MeHg did not increase or decrease markedly when the total Hg content increased. It could be concluded that these North Sea samples are not much contaminated by Hg and are surely suitable for consumption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00342265
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  • 4
    Electronic Resource
    Electronic Resource
    Contribution of nitrate to the uptake of nitrogen by phytoplankton in an ocean margin environment (1997)
    Springer
    Hydrobiologia 353 (1997), S. 139-152 
    Details
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Rates of nitrate and ammonium uptake by phytoplankton were measured fromJuly 1990 to March 1995 in the surface waters at several stations locatedalong the continental margin of the NE Atlantic Ocean. Total inorganicnitrogen assimilation ranged from 2.3 to 95 nM h−1 andexhibited two maxima during the spring bloom and in fall at the beginning ofthe vertical mixing of the water column. Seasonal and spatial changes in thenitrogen uptake regime (f-ratios) were estimated (1) by correcting ammoniumuptake rates with an isotope dilution model, and (2) by evaluating theinhibition of nitrate uptake by ammonium, using a variation of theMichaelis-Menten equation. Overall, nitrate uptake rates paralleled carbonfixation rates, and f-ratios followed the well-known function of nitrate.During spring, new production, sensu Dugdale & Goering (1967), accountedfor 46 to 85% of the total inorganic nitrogen production. It can gainin importance through vertical mixing in fall (0.29 〈 f 〈 0.82), aftera period of predominant regenerated production in summer (0.07 〈 f 〈0.41). Although new production appeared to be quantitatively important onaverage (mean f = 0.53), kinetic data suggested that ammonium wasutilised preferentially throughout the full spectrum of nitrogenconcentrations observed during this study. Moreover, the inhibition ofnitrate uptake by ambient level of ammonium was estimated to range from 8 to50%. Therefore, it is suggested that the supply of regeneratednitrogenous nutrients, combined with feedback mechanisms (preference andinhibition), triggers a switch-over from predominantly new productiontowards regenerated production, even before the complete exhaustion ofnitrate in the surface water. Overall, these results indicate a leading rolefor ammonium in regulating the removal of nitrate in this margin ecosystem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003058928157
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  • 5
    Electronic Resource
    Electronic Resource
    General description of the Scheldt estuary (1997)
    Springer
    Hydrobiologia 366 (1997), S. 1-14 
    Details
    ISSN: 1573-5117
    Keywords: Scheldt estuary ; description ; hydrology ; sedimentation ; oxygen profiles ; productivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A general description of the Scheldt estuary,including the hydrology, the sediment transport, theproductivity and the biodegradation with respect totheir influence on the trace metal behaviour in theScheldt estuary, is given. The river basin can be divided in several sectionsaccording to their morphological, hydrodynamical andsedimentary properties. The zone from km 78 to 55,which corresponds roughly with the salinity zone from2 to 10 psu, is the zone of high turbidity, highsedimentation and of oxygen depletion, especially inthe summer period. That area is called the geochemicalfilter because the solid/dissolved distribution of thetrace metals is controlled by redox,adsorption/desorption, complexation andprecipitation/coprecipitation processes. Thesedimentation rate in that area is estimated at280 Mkg y-1. In the downstream estuary the phytoplankton activityincreases due to the restoration of oxygen and to themuch lower turbidity values. That area is called thebiological filter because incorporation of tracemetals by the plankton communities lowers the tracemetal concentrations during the productivity period,while transformation of metal species, especiallyobserved with mercury, occurs during that period too.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003164009031
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  • 6
    Electronic Resource
    Electronic Resource
    The biogeochemical behaviour of Cd, Cu, Pb and Zn in the Scheldt estuary: results of the 1995 surveys (1997)
    Springer
    Hydrobiologia 366 (1997), S. 45-62 
    Details
    ISSN: 1573-5117
    Keywords: Scheldt estuary ; trace metals ; 1995 ; dissolved ; particulate ; biogeochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cu, Cd, Zn and Pb concentrations in both dissolved andparticulate phase were assessed during 1995. DataQuality Assurance was an integral part of this studyand involved all major steps of the analysis proceduresuch as sampling, sample handling, preconcentrationand determination. Desorption and redox processes clearly control thedissolved Cu and Cd profiles. Mobilisation ofdissolved Zn is small and essentially restricted tothe low salinity area and the late spring survey.Dissolved Pb shows the clearest dilution pattern. Theparameters representative of these processes(dissolved oxygen and salinity) also correlate verywell with the particulate metal profiles. In addition, the plankton activity (expressed by thechlorophyll-a levels) may influence the dissolved andparticulate metal profiles. In combination withdesorption and redox processes, seasonal variationswere induced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003120226778
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  • 7
    Electronic Resource
    Electronic Resource
    Biogeochemical behaviour of Cd, Cu, Pb and Zn in the Scheldt estuary during the period 1981–1983 (1997)
    Springer
    Hydrobiologia 366 (1997), S. 15-44 
    Details
    ISSN: 1573-5117
    Keywords: Scheldt estuary ; trace metals ; 1981–1983 ; dissolved ; particulate ; biogeochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cu, Zn, Cd and Pb have been analysed in suspendedmatter and water samples from the Scheldt estuary,collected during five cruises between May 1982 and May1983. In order to evaluate the overall metal behaviourin the estuary, continuous longitudinal profiles ofthe total, the particulate and the dissolved metalconcentrations are discussed in relation to variousspecific physico-chemical parameters. By means ofcorrelation and multi-regression techniques, severalestuarine processes could be identified which dominateand/or control the behaviour of the individual tracemetals in three distinct areas of the Scheldt estuary. The behaviour of the four selected metals was foundto show some common features, but is besides this alsocharacterised by many individual and specificproperties. The total metal concentrations seem toco-vary well with the turbidity in the maximumturbidity zone between salinities 2 and 10 psu. In thedownstream area a dilution profile is observed for thetotal metal concentrations of Cu and Cd as well as forthe dissolved concentrations of all metals. Dissolved metal production rates are high for Cu andCd, but much lower for Zn and Pb, confirming thedifferent longitudinal dissolved metal profiles. ForCu and Cd these dissolved metal profiles arecharacterised by a broad mobilisation area, coveringthe whole middle estuary. Pb on the other hand, showsa more confined mobilisation area, and for Zn no sucharea was found. During winter the dissolved metalproduction rates seem to be controlled, predominantly,by desorption processes. During summer dissolved metalproduction is correlated mainly to the dissolvedoxygen content, suggesting the domination of redoxprocesses solely or in combination with desorptionprocesses. In some cases, co-existent with nearly zerooxygen concentrations, removal of dissolved metals wasobserved, possibly reflecting precipitation reactions. Longitudinal particulate metal profiles all show anegative deviation versus the dilution profile. Cu andCd provide the higher deviations, characterised by anarrow enrichment zone preceding a broad mobilisationarea. Finally, all particulate metal profiles appearedto correlate well with POC, when expressed involumetric units.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003168125869
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  • 8
    Electronic Resource
    Electronic Resource
    Behaviour and speciation of mercury in the Scheldt estuary (water, sediments and benthic organisms) (1997)
    Springer
    Hydrobiologia 366 (1997), S. 63-79 
    Details
    ISSN: 1573-5117
    Keywords: Mercury ; methylmercury ; biogeochemical cycling ; estuaries ; benthic organisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Surface waters, sediments and the polychaete Nereis diversicolor were sampled in the ScheldtEstuary between 1990 and 1994. In surface watersparticulate Hg (HgP) concentrations ranged from350–1610 ng g-1. They are essentiallycontrolled by physical mixing of polluted fluvialparticulates with relatively unpolluted marineparticulates, but unaffected by seasonal changes.Dissolved Hg species, on the other hand, show largeseasonal variations essentially controlled by theredox conditions in the estuary, as well as bybacterial and phytoplankton activity. Total dissolvedHg (HgTD) concentrations ranged from 0.5 to 3.0 ngl-1 with 10 to 90% as reactive Hg. Highconcentrations of HgTD are found in the upperestuary in the winter and decrease rapidly withincreasing salinity. In summer HgTDconcentrations are low in the anoxic upper estuary andincrease as oxygen is restored in the estuary.Significant variations were observed in dissolvedMonomethyl Hg (MMHg) concentrations withconcentrations ranging from 0.01 to 0.120 ng l-1 in the winter and 0.08 to 0.6 ng l-1 in summerand autumn. Particulate MMHg ranged from 2 to 6 ngg-1 in winter and from 4 to 10 ng g-1 insummer and accounted for 20 to 80% of the total MMHg.Hg° concentrations ranged from 0.02 to 0.130 ngl-1 and are higher in summer than in winter. Inthe lower estuary a positive correlation betweenHg° and phytoplankton pigments was observed. Sediments and the polychaete N. diversicolorwere sampled on the intertidal flat GrootBuitenschoor. Hg_T concentrations in surfacesediments ranged from 144 to 1890 ng g-1 and MMHgfrom 0.8 to 6 ng g-1 accounting for 0.4 to 0.8%of the total mercury present. Both total Hg (HgT)and MMHg concentrations increased with increasedorganic matter content and anoxic conditions. On theother hand, accumulation of HgT and MMHg washigher in N. diversicolor living in coarse grainsandy sediments than in muddy sediments. MMHgconcentrations in N. diversicolor ranged from2.2 to 20.9 ng g-1 accounting for an average of18% of the HgT. Seasonal variationssignificantly affected Hg speciation in sediments andN. diversicolor. Higher HgT concentrationswere found in the sediments in autumn and winter,whereas MMHg concentrations increased in spring andsummer. Likewise, higher MMHg concentrations were alsoobserved in N. diversicolor in spring andsummer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003124310848
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of organic complexation on the behaviour of dissolved Cd, Cu and Zn in the Scheldt estuary (1997)
    Springer
    Hydrobiologia 366 (1997), S. 81-90 
    Details
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Samples from the Scheldt estuary have been assayed for dissolved Cd, Cuand Zn using differential pulse anodic stripping voltammetry, either astotal (after UV irradiation) or labile concentrations. Under theseexperimental conditions, labile concentrations ranged between51–65% of total Cu, 16–66% of total Zn and53–91% of total Cd. The metal–organic interactions wereassessed by evaluating (a) the distribution coefficient Kd forthe distribution of the metals between the liquid phase (complexation) andtheir binding to particulate matter, and (b) the competitive effect exertedby inorganic complexing ligands using a multi–element interactionmodel. The proportion of organically bound metals (strong and labile) wasestimated, in this speciation scheme, to range from 86 to 99% for Cu,from 90 to 96% for Zn, and from 10 to 35% for Cd. From thedissolved organic carbon distribution in the Scheldt (≤ 10 mg Cl-1 and taking into account competition from major cations Caand Mg, free ligand concentrations available for heavy metal complexationwere estimated to be ≤ 0.15 mg C l-1. With these values,conditional stability constants for the chelation of Cu, Zn and Cd werecalculated assuming either a single-step or a two-step complexation in thedissolved phase. Given the assumptions made in these models, stabilityconstants in the range of 107.8–1010.6 forCu, 107.0–109.1 for Zn and106.9–108.9 for Cd were obtained. Therelevance of these data to previous in vitro and in situ studies isdiscussed taking into consideration current concepts of metal bindingaffinity for organic ligands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003176327686
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  • 10
    Electronic Resource
    Electronic Resource
    The impact of the Scheldt input on the trace metal distribution in the Belgian coastal area (results of 1981–1983 and 1995–1996) (1997)
    Springer
    Hydrobiologia 366 (1997), S. 91-108 
    Details
    ISSN: 1573-5117
    Keywords: Trace metals ; North Sea ; coastal waters ; fluxes ; residual flows ; river inputs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Offshore fluxes of Cu, Zn, Cd, Pb and Hg were calculated based onresidual flow patterns and salinity gradients along the Belgian coast. Theresidual flow lines along the Belgian coast are more or less parallel to thecoast except in the area where the north-easterly flowing watermass comingfrom the Channel encounters the south-westerly-oriented Scheldt outflow,forming a residual hydrodynamical front. From the steady-state salinitypattern, diffusion coefficients perpendicular to the residual flow werededuced; they ranged from 21 to 108 m2 s-1. Offshore fluxes of dissolved and particulate trace metals based on diffusiveand mixing processes are calculated. The steady state profiles of dissolvedmetals show a dilution effect in the coastal waters, reaching an almostconstant concentration in the marine watermass in the 1981–1983dataset. The ratios of the Scheldt input of trace metals to the totaldissolved offshore flux vary from 38 to 55% (1981–1983),depending on the kind of metal, and from 55 to 91% (1995–1996).The ratio of the Scheldt input to the dissolved metal flow parallel to thecoast, is in both periods (1981–1983 and 1995–1996), smallerthan 1%. The steady-state concentration profiles of particular metalsversus salinity are fairly constant in the coastal-estuarine and marinewatermasses, but decrease very abruptly from the first to the secondwatermass. Assuming a conservative behaviour of the particular metals,offshore fluxes and the resulting concentration increases agree fairly wellwith the observed values. The ratios of the Scheldt input to the particulatetrace metal offshore flux vary between 30 to 46% (1981–1983)and 13 to 37% (1995–1996). The contribution of the Scheldtestuary to the flows parallel to the coast ranges from 1.6 to 2.9%(1981–1983) and from 0.6 to 1.6% (1995).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003128411757
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