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1.
In the spring of 1995, short-term variations in the concentration of particulate and dissolved dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) were monitored in the western Wadden Sea, a shallow coastal region in open connection with the North Sea. Significant correlations were found between abundance of Phaeocystis globosa and particulate DMSP; concentrations increased rapidly from 100 to 1650 nM in the middle of April. Highest DMS concentrations were found during the initial phase of the exponential growth of the bloom. DMS production and loss rates of DMSP and DMS were estimated experimentally during various phases of the bloom. DMS production and consumption were roughly in balance, with production only slightly exceeding consumption at the start of the bloom. Rates of production and consumption were highest during the exponential growth phase of Phaeocystis and declined in the course of the bloom (from 300–375 to less than 5 nmol dm−3 d−1). Demethylation of DMSP increased during the bloom (from 11 to 1300 nmol dm−3 d−1); it accounted for up to 100% of the DMSP loss at the end of the bloom. The shift from DMSP cleavage to demethylation in the course of a Phaeocystis bloom implies that DMS concentrations are not necessarily highest at the peak or towards the end of blooms.  相似文献   

2.
Natural iron fertilization processes are occurring around the Crozet Islands (46°26′S–52°18′E), thus relieving the water masses from the normally encountered High Nutrients Low Chlorophyll (HNLC) conditions of the Southern Ocean. During austral summers 2004/2005 and 2005/2006, iron and aluminium concentrations were investigated in large particles (> 53 µm) collected from just below the mixed layer at stations under the influence of island inputs, and also in adjacent HNLC waters. These large particles are anticipated to sink out of the mixed layer, and to reflect the net effects of input and cycling of these elements in the overlying mixed layer. Labile and refractory fractions were determined by a two-stage leaching technique. Data showed that water masses downstream of the islands were enriched in total iron and aluminium (0.25–2.68 nmol L− 1 and 0.34–3.28 nmol L− 1 respectively), relative to the southern HNLC control sites (0.15–0.29 nmol L− 1 for Fe and 0.12–0.29 nmol L− 1 for Al), with only a small fraction (typically < 1%) being acid leachable in both environments. Particulate iron predominantly derived from the island system represents a significant fraction of the total water column iron inventory and may complement dissolved Fe inputs that help support the high summer productivity around the Crozet islands.  相似文献   

3.
Determination of the actual mercury concentration in Mediterranean basin seawater was achieved by means of an instrument based on fluorescence spectrometry developed for this purpose, during a field study aboard the oceanographic ship “L.F. Marsili”, between August 1980 and May 1982.Dissolved ·total’ and ·reactive’ mercury and mercury associated with particulate matter were determined on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Concentrations in the range 1.4–19.7 ng l−1 for ·total dissolved mercury’, 0.5–5.9 ng l−1 for ·reactive dissolved mercury’ and 0.3–8.0 ng l−1 for mercury associated with the particulate matter, were measured on surface and subsurface waters in the Tyrrhenian Sea from La Spezia to Sicily.Even if the mean value of the total mercury concentration (dissolved + particulate) was found to be about twice as high as those observed for the oceans, the difference does not seem to be as high as predicted by the model proposed by Buffoni and co-workers to explain the large difference of mercury levels between tunas caught, respectively, in the Mediterranean and in the Oceans.  相似文献   

4.
Land/ocean boundaries constitute complex systems with active physical and biogeochemical processes that affect the global carbon cycle. An example of such a system is the mesotidal lagoon named Ria de Aveiro (Portugal, 40°38′N, 08°45′W), which is connected to the Atlantic Ocean by a single channel, 350 m wide. The objective of this study was to estimate the seasonal and inter-tidal variability of organic carbon fluxes between the coastal lagoon and the Ocean, and to assess the contribution of the organic carbon fractions (i.e. dissolved organic carbon (DOC) and particulate organic carbon (POC)) to the export of organic carbon to the Ria de Aveiro plume zone. The organic carbon fractions fluxes were estimated as the product of the appropriate fractional organic carbon concentrations and the water fluxes calculated by a two-dimensional vertically integrated hydrodynamic model (2DH). Results showed that the higher exchanges of DOC and POC fractions at the system cross-section occurred during spring tides but only resulted in a net export of organic carbon in winter, totalling 85 t per tidal cycle. Derived from the winter and summer campaigns, the annual carbon mass balance estimated corresponded to a net export of organic carbon (7957 = 6585 t yr−1 POC + 1372 t yr−1 DOC). On the basis of the spring tidal drainage area, it corresponds to an annual flux of 79 g m−2 of POC and 17 g m−2 of DOC out of the estuary.  相似文献   

5.
Concentrations of Hg0 in surface waters and atmosphere of the Scheldt estuary and the North Sea are presented and their relationship with biological processes is discussed. Hg0 concentrations in the Scheldt estuary range from 0.1 to 0.38 pmol·l−1 in the winter and from 0.24 to 0.65 pmol·l−1 in the summer and show a positive relationship with phytoplankton pigments. In the North Sea Hg0 concentrations range from 0.06 to 0.8 pmol·l−1 and are higher in coastal stations. Transfer velocities across the air–sea interface were calculated using a classical shear turbulence model. Volatilization fluxes of Hg0 were calculated for the Scheldt estuary and the North Sea. For the Scheldt estuary the fluxes range from 226–284 pmol·m−2·d−1 in winter and 500–701 pmol·m−2·d−1 in summer and for the North Sea the fluxes range from 59–1110 pmol·m−2·d−1 for an average windspeed of 8.1 m·s−1. These fluxes are comparable to the wet and dry depositional fluxes to the North Sea. Hg0 formation rates necessary to balance the volatilization fluxes vary from 0.2 to 4% d−1.  相似文献   

6.
Exopolymeric substances (EPS) produced by microorganisms play important roles in various aquatic, porous, and extreme environments. Only recently has their occurrence in sea ice been considered. We used macroscopic and microscopic approaches to study the content and possible ecological role of EPS in wintertime fast ice near Barrow, Alaska (71°20′ N, 156°40′ W). Using Alcian blue staining of melted ice samples, we observed high concentrations of EPS in all samples examined, ranging from 0.79 to 7.71 mg xanthan gum equivalents (XGEQV) l−1. Areal conversions to carbon equivalents yielded 1.5−1.9 g C m−2 ice in March and 3.3−4.0 g C m−2 in May (when the ice was thicker). Although EPS did not correlate with macronutrient or pigment data, the latter analyses indicated ongoing or recent biological activity in the ice within temperature horizons of −11°C to −9°C and warmer. EPS correlated positively with bacterial abundance (although no functional relationship could be deduced) and with dissolved organic carbon (DOC) concentrations. Ratios of EPS/DOC decreased at colder temperatures within the core, arguing against physical conversion of DOC to EPS during freezing. When sea-ice segments were maintained at representative winter temperatures (−5°C,−15°C and −25°C) for 3−14 months, the total EPS content increased significantly at rates of 5−47 μg XGEQV l−1 d−1, similar to published rates of EPS production by diatoms. Microscopic images of ice-core sections at these very cold temperatures, using a recently developed non-invasive method, revealed diatoms sequestered in spacious brine pockets, intact autofluorescent chloroplasts in 47% of the (pennate) diatoms observed, and indications of mucus in diatom-containing pores. The high concentrations of EPS detected in these winter ice cores represent a previously unrecognized form of organic matter that may contribute significantly to polar ocean carbon cycles, not only within the ice but after springtime release into the water column. The EPS present in very high concentrations in the brine of these microhabitats appear to play important buffering and cryoprotectant roles for microorganisms, especially diatoms, against harsh winter conditions of high salinity and potential ice-crystal damage.  相似文献   

7.
Data presented in this paper are part of an extensive investigation of the physics of cross-shelf water mass exchange in the north-east of New Zealand and its effect on biological processes. Levels of dissolved dimethylsulfide (DMS) were quantified in relation to physical processes and phytoplankton biomass. Measurements were made at three main sites over the north-east continental shelf of New Zealand's North Island during a current-driven upwelling event in late spring 1996 (October) and an oceanic surface water intrusion event in summer 1997 (January). DMS concentrations in the euphotic zone ranged between 0.4 and 12.9 nmol dm−3. Integrated water column DMS concentrations ranged from 33 to 173 μmol m−2 in late spring during the higher biomass (15–62 Chl-a mg m−2) month of October, and from 25 to 38 μmol m−2 in summer during the generally lower biomass (16–42 Chl-a mg m−2) month of January. We observed high levels of DMS in the surface waters at an Inner Shelf site in association with a Noctiluca scintillans bloom which is likely to have enhanced lysis of DMSP-producing algal cells during phagotrophy. Integrated DMS concentrations increased three-fold at a Mid Shelf site over a period of a week in conjunction with a doubling of algal biomass. A high correlation (r2=0.911, significant <0.001) of integrated DMS and chlorophyll-a concentrations for compiled data from all stations indicated that chlorophyll-a biomass may be a reasonable predictor of DMS in this region, even under highly variable hydrographic conditions. Integrated bacterial production was inversely correlated to DMS production, indicating active bacterial consumption of DMS and/or its precursor.  相似文献   

8.
Phytoplankton NH4+ and NO3− uptake was examined along the longitudinal salinity gradient of the Delaware Estuary over several seasonal cycles using 15N-tracer techniques. Saturated nitrogen uptake rates increased directly with water temperature and reached a maximum of 380 nmol Nl−1h−1 during summer. This temperature dependence was related primarily to changes in the rate of maximum chlorophyll specific uptake, which varied exponentially between 2 and 70 nmol N [μg Chl h]−1 over a temperature range of 2–28°C. Despite these high uptake rates, balanced growth (C:N7:1) could be maintained over the diel light cycle only by highly efficient nitrogen uptake at low light intensities and dark uptake below the photic zone and at night (dark UPTAKE=25% maximum uptake).Ammonium fulfilled 82% of the annual phytoplankton nitrogen demand in the estuary despite dominance of NO3− in the ambient dissolved inorganic nitrogen pool. The predominance of NH4+ uptake occurred because of the general suppression of NO3− assimilation at NH4+ concentrations in excess of 2 μ . This suppression, however, was not as universal as has been reported for other systems, and it is suggested that the extremely high NO3− concentrations found in the estuary contribute to this pattern. Nitrate was a significant source of nitrogen only during periods of high phytoplankton production in summer, and when NH4+ concentrations were low towards the end of the spring bloom.  相似文献   

9.
Specific effects of tributyltin (TBT) on Crassostrea gigas—valve thickening, and Nucella lapillus—imposex, were measured on local populations, relatively clean unaffected species from England were transferred to the Netherlands and exposed during six weeks to ambient TBT concentrations. Near marinas 50% of the exposed species were sterile after six weeks. In general, no dissolved butyltins were detected in the Rhine and Scheldt estuaries. In 1988 TBT concentrations in marinas ranged from 120 to 4000 ng litre−1. In sediments (fraction <60 μm) and suspended particulate matter TBT concentrations reached up to 1200 ng g−1. TBT concentrations in mussel tissue ranged from <1 to 2300 ng g−1 based on a dry weight. In 1989 concentrations of dissolved TBT ranged from <0·1 to 7200 ng litre−1. In 1989 a seasonal study in the marina of Colijnsplaat showed that dissolved butyltins increased from April to the end of May due to the launching of freshly painted boats, and decreased afterwards.  相似文献   

10.
The Mussel Watch program conducted along the French coasts for the last 20 years indicates that the highest mercury concentrations in the soft tissue of the blue mussel (Mytilus edulis) occur in animals from the eastern part of Seine Bay on the south coast of the English Channel, the “Pays de Caux”. This region is characterized by the presence of intertidal and submarine groundwater discharges, and no particular mercury effluent has been reported in its vicinity. Two groundwater emergence systems in the karstic coastal zone of the Pays de Caux (Etretat and Yport with slow and fast water percolation pathways respectively) were seasonally sampled to study mercury distribution, partitioning and speciation in water. Samples were also collected in the freshwater–seawater mixing zones in order to compare mercury concentrations and speciation between these “subterranean” or “groundwater” estuaries and the adjacent macrotidal Seine estuary, characterized by a high turbidity zone (HTZ). The mercury concentrations in the soft tissue of mussels from the same areas were monitored at the same time.The means of the “dissolved” (< 0.45 μm) mercury concentrations (HgTD) in the groundwater springs were 0.99 ± 0.15 ng l− 1 (n = 18) and 0.44 ± 0.17 ng l− 1 (n = 17) at Etretat and Yport respectively. High HgTD concentrations were associated with strong runoff over short water pathways during storm periods, while low concentrations were associated with long groundwater pathways. Mean particulate mercury concentrations were 0.22 ± 0.05 ng mg− 1 (n = 16) and 0.16 ± 0.10 ng mg− 1 (n = 17) at Etretat and Yport respectively, and decreased with increasing particle concentration probably as a result of dilution by particles from soil erosion. Groundwater mercury speciation was characterized by high reactive-to-total mercury ratios in the dissolved phase (HgRD/HgTD: 44–95%), and very low total monomethylmercury concentrations (MMHg < 8 pg l− 1). The HgTD distributions in the Yport and Etretat mixing zones were similar (overall mean concentration of 0.73 ± 0.21 ng l− 1, n = 43), but higher than those measured in the adjacent industrialized Seine estuary (mean: 0.31 ± 0.11 ng l− 1, n = 67). In the coastal waters along the Pays de Caux dissolved monomethylmercury (MMHgD) concentrations varied from 9.5 to 13.5 pg l− 1 (2 to 8% of the HgTD). Comparable levels were measured in the Seine estuary (range: 12.2– 21.1 pg l−1; 6–12% of the HgTD). These groundwater karstic estuaries seem to be mostly characterized by the higher HgTD and HgRD concentrations than in the adjacent HTZ Seine estuary. While the HTZ of the Seine estuary acts as a dissolved mercury removal system, the low turbid mixing zone of the Pays de Caux receives the dissolved mercury inputs from the groundwater seepage with an apparent Hg transfer from the particulate phase to the “dissolved” phase (< 0.45 μm). In parallel, the soft tissue of mussels collected near the groundwater discharges, at Etretat and Yport, exhibited significantly higher values than those found in the mussel from the mouth of the Seine estuary. We observe that this difference mimics the differences found in the mercury distribution in the water, and argue that the dissolved phase of the groundwater estuaries and coastal particles are significant sources of bioavailable mercury for mussels.  相似文献   

11.
Concentrations of bacteria, chlorophyll a, and several dissolved organic compounds were determined during 11 tidal cycles throughout the year in a high and a low elevation marsh of a brackish tidal estuary. Mean bacterial concentrations were slightly higher in flooding (7·1 × 106 cells ml−1) than in ebbing waters (6·5 × 106 cells ml−1), and there were no differences between marshes. Mean chlorophyll a concentrations were 36·7 μg l−1 in the low marsh and 20·4 μg l−1 in the high marsh. Flux calculations, based on tidal records and measured concentrations, suggested a small net import of bacterial and algal biomass into both marshes. Over the course of individual tidal cycles, concentrations of all parameters were variable and not related to tidal stage. Heterotrophic activity measured by the uptake of 3H-thymidine, was found predominantly in the smallest particle size fractions (< 1·0 μm). Thymidine uptake was correlated with temperature (r = 0·48, P < 0·01), and bacterial productivity was estimated to be 7 to 42 μg Cl−1 day−1.  相似文献   

12.
A batch sorption technique for the determination of particle–water interactions of hydrophobic organic micropollutants under simulated estuarine conditions is described. Results are presented for the behaviour of 2,2′,5,5′-tetrachlorobiphenyl (2,2′,5,5′-TCB) in river and sea waters, both in the presence and absence of estuarine suspended particles. Adsorption onto particles in sea water was enhanced compared with adsorption in river water owing to salting out of the compound, and possibly of the particulate organic matter, in the presence of high concentrations of dissolved ions. The particle–water distribution coefficient, KD, decreased from about 120×103 to 10×103 ml g−1, and from about 150×103 to 20×103 ml g−1, in river water and sea water, respectively, over a particle concentration range of 10–1000 mg l−1. Incomplete recovery of compound from the reactor walls is partly responsible for a particle concentration effect, while artefacts relating to inadequate sediment and water phase separation were ruled out following further experiments. The particle concentration effect, which is replicated in many field studies of hydrophobic organic micropollutants, including 2,2′,5,5′-TCB, is incorporated into a simple partitioning model and is discussed in the context of the likely estuarine behaviour of such compounds.  相似文献   

13.
As part of a study of estuarine selenium cycling, we measured the concentration, chemical form (speciation), and distribution of particulate selenium under various river flow conditions in the North San Francisco Bay (from the Golden Gate to the Sacramento and San Joaquin Rivers). We also conducted laboratory studies on the accumulation of selenium by phytoplankton, the critical first step in the transformation of dissolved to particulate selenium. Total particulate selenium concentration in the North SF Bay was relatively constant between high and low flow periods, ranging spatially from 0.05 to 0.35 nmol l−1 and comprising between 5 and 12% of the total water column selenium inventory. Mean concentrations were generally highest in the Carquinez Strait–Suisun Bay region (salinity 0–17) and lowest in Central Bay. However, selenium content of suspended particles varied with river flow, with higher content during low flow (9.76 ± 4.17 nmol g−1; mean ± sd; n = 67) compared to high flow (7.10 ± 4.24 nmol g−1; n = 39). Speciation analyses showed that most particulate selenium is organic selenide (45 ± 27%), with a smaller proportion (typically <30%) of adsorbed selenite + selenate and a varying proportion (35 ± 28%) of elemental selenium. Based on the amount of elemental selenium in the seston (total suspended material), we calculate that resuspension of estuarine sediments could contribute 29–100% of particulate selenium in the water column. While selenium content of SF Bay seston (>0.4 μm) is relatively unenriched compared to phytoplankton (13.6–155 nmol g−1 dry weight) on a mass basis, when normalized to carbon or nitrogen, seston contains a similar selenium concentration to SF Bay sediments or phytoplankton cultures. SF Bay seston is thus comprised of selenium-rich phytoplankton and phyto-detritus, but also inorganic clay mineral particles that effectively “dilute” total particulate selenium. Selenium concentrations in algal cultures (11 species) exposed to 90 nmol l−1 selenite show relatively large differences in selenium accumulation, with the diatoms, chlorophytes and cryptophytes generally having lower selenium cell content (3.8 ± 2.7 × 10−9 nmol selenium cell−1) compared to the dinoflagellates (193 ± 73 × 10−9 nmol selenium cell−1). Because phytoplankton are such a rich (but variable) source of selenium, their dynamics could have a profound effect on the particulate selenium inventory in the North SF Bay.  相似文献   

14.
Wind-driven cyclonic eddies are hypothesized to relieve nutrient stress and enhance primary production by the upward displacement of nutrient-rich deep waters into the euphotic zone. In this study, we measured nitrate (NO3−), particulate carbon (PC), particulate nitrogen (PN), their stable isotope compositions (δ15N-NO3−, δ13C-PC and δ15N-PN, respectively), and dissolved organic nitrogen (DON) within Cyclone Opal, a mature wind-driven eddy generated in the lee of the Hawaiian Islands. Sampling occurred in March 2005 as part of the multi-disciplinary E-Flux study, approximately 4–6 weeks after eddy formation. Integrated NO3− concentrations above 110 m were 4.8 times greater inside the eddy (85.8±6.4 mmol N m−2) compared to the surrounding water column (17.8±7.8 mmol N m−2). Using N-isotope derived estimates of NO3− assimilation, we estimated that 213±59 mmol m−2 of NO3− was initially injected into the upper 110 m Cyclone Opal formation, implying that NO3− was assimilated at a rate of 3.75±0.5 mmol N m−2 d−1. This injected NO3− supported 68±19% and 66±9% of the phytoplankton N demand and export production, respectively. N isotope data suggest that 32±6% of the initial NO3− remained unassimilated. Self-shading, inefficiency in the transfer of N from dissolved to particulate export, or depletion of a specific nutrient other than N may have led to a lack of complete NO3− assimilation. Using a salt budget approach, we estimate that dissolved organic nitrogen (DON) concentrations increased from eddy formation (3.8±0.4 mmol N m−2) to the time of sampling (4.0±0.09 mmol N m−2), implying that DON accumulated at rate of 0.83±1.3 mmol N m−2 d−1, and accounted for 22±15% of the injected NO3−. Interestingly, no significant increase in suspended PN and PC, or export production was observed inside Cyclone Opal relative to the surrounding water column. A simple N budget shows that if 22±15% of the injected NO3− was shunted into the DON pool, and 32±6% is unassimilated, then 46±16% of the injected NO3− remains undocumented. Alternative loss processes within the eddy include lateral exchange of injected NO3− along isopycnal surfaces, remineralization of PN at depth, as well as microzooplankton grazing. A 9-day time series within Cyclone Opal revealed a temporal depletion in δ15N-PN, implying a rapid change in the N source. A change in NO3− assimilation, or a shift from NO3− fueled growth to assimilation of a 15N-deplete N source, may be responsible for such observations.  相似文献   

15.
Lagrangian time series of dimethylsulfide (DMS) concentrations from a cyclonic and an anticyclonic eddy in the Sargasso Sea were used in conjunction with measured DMS loss rates and a model of vertical mixing to estimate gross DMS production in the upper 60 m during summer 2004. Loss terms included biological consumption, photolysis, and ventilation to the atmosphere. The time- and depth (0–60 m)-averaged gross DMS production was estimated to be 0.73±0.09 nM d−1 in the cyclonic eddy and 0.90±0.15 nM d−1 in the anticyclonic eddy, with respective DMS replacement times of 5±1 and 6±1 d. The higher estimated rate of gross production and lower measured loss rate constants in the anticyclonic eddy were equally responsible for this eddy's 50% higher DMS inventory (0–60 m). When normalized to chlorophyll and total dimethylsulfoniopropionate (DMSP), estimated gross production in the anticyclonic eddy was about twice that in the cyclonic eddy, consistent with the greater fraction of phytoplankton that were DMSP producers in the anticyclonic eddy. Higher rates of gross production were estimated below the mixed layer, contributing to the subsurface DMS maximum found in both eddies. In both eddies, gas exchange, microbial consumption, and photolysis were roughly equal DMS loss terms in the surface mixed layer (0.2–0.4 nM d−1). Vertical mixing was a substantial source of DMS to the surface mixed layer in both eddies (0.2–0.3 nM d−1) owing to the relatively high DMS concentrations below the mixed layer. Estimated net biological DMS production rates (gross production minus microbial consumption) in the mixed layer were substantially lower (by almost a factor of 3) than those estimated in a previous study of the Sargasso Sea, which may explain the relatively low mixed-layer DMS concentrations found here during July 2004 (3 nM) compared to previous summers (4–6 nM).  相似文献   

16.
Few data on dissolved trace metals in rivers and estuaries are presently available. This paper is an attempt to provide additional data on dissolved concentrations obtained in polluted and so-called unpolluted river estuarine systems. Data for two major French rivers (Gironde, Rhône) have been compared with the Chinese Yellow River (Huanghe) and Yangtze River (Changjiang). Dissolved Cd concentrations have been measured by differential pulse anodic stripping voltammetry. Average concentrations range from 15 ng kg−1 to 50 ng kg−1 (0.13–0.45 nmol kg−1) in the French rivers and are below 4 ng kg−1 (0.040 nmol kg−1) in the Chinese rivers.In all the estuaries studied the dissolved Cd concentrations depict a systematic bulge in the mixing zone which is attributed largely to remobilization processes from particulate matter when the chlorinity increases. Other parameters that may also play a significant role for remobilization are discussed. The processes concerned lead us to reassess the net Cd river input to the oceans, and this should be taken into account for a more precise evaluation of the residence time of oceanic Cd.  相似文献   

17.
In September 1994 and 1995, scientists from the Australian Institute of Marine Science (AIMS) and the Australian Geological Survey Organization (AGSO) conducted surveys aboard the RV Lady Basten to determine the dispersion, fates and effects of produced formation water (PFW) discharged from the ‘ Harriet A ’ oil production platform near the Montebello Islands. This report is one of four related papers and describes the non-volatile hydrocarbon chemistry studies. The dispersion of the PFW into dissolved and particulate fractions of seawater were measured using moored high volume water samplers, surface screen samplers and moored and drifting sediment traps. Bio-accumulation was studied using transplanted oysters, and dispersion measured into sediment with benthic grabs.Results showed enrichment in non-volatile hydrocarbons in surface microlayer samples to a distance of 1·8 km in the direction of tidal flow. Concentrations in surface microlayers near the platform varied by an order of magnitude and corresponded to when a surface slick was visible or not visible. Concentrations of oil in seawater ranged from 2·0 to 8·5 μg l−1at near stations to 1·3 μg l−1at 1·8 km. Water column samples showed the processes of desorption from particles for soluble components occur within the range of 1·8 km. Most particulate hydrocarbons drop out of suspension within c. 1 to 2 km from the platform. Fluxes of particulate hydrocarbons through the water column at c. 1 km, as estimated by moored sediment traps in 1995, were 138 to 148 ng cm−2day−1. A decrease in sediment concentrations within c. 1 km of the platform was measured as 2·45±1·29 μg g−1dry wt (n=15) in 1994 to 0·86±0·54 μg g−1dry wt (n=21) in 1995, after the platform installed a centrifugal separator in the discharge treatment process. Thus the residence time of this relatively low molecular weight oil was estimated in the coarse aerobic sands surrounding the platform to be less than one year. Oysters suspended near the platform bio-accumulated hydrocarbons and other lipophilic organics in their tissues. Uptake rates and bio-concentration factors of hydrocarbons indicated potential toxicity at the near-field stations within c. 1 km radius.A mass balance was constructed to show the partitioning of the input of hydrocarbons from the PFW into the surrounding marine ecosystem. The rates of dissipation processes were estimated as follows: dilution from tidal currents>degradation in the water column>sedimentation>evaporation. The calculations based on maximum concentrations measured in the environmental samples accounted for 85% of the daily input suspended within a 1 km radius.It is estimated that the potential zone of toxic influence in the water column extends to a distance of approximately 1 km. Concentrations of oil in sediments were too low to indicate potential toxicity. By the collaborative application of oceanographic and geochemical techniques to marine environmental problems, we endeavour to provide effective feedback to the oil industry to gauge the effectiveness of their operational strategies in minimizing impact in these pristine regions.  相似文献   

18.
Analyses of the concentration product (Ca2+) × (CO32−) in the pore waters of marine sediments have been used to estimate the apparent solubility products of sedimentary calcite (K′SPc) and aragonite (K′SPa) in seawater. Regression of the data gives the relation In K′PSPc = 1.94 × 10−3 δP − 14.59 The 2°C, 1 atm value of K′SPc is, then, 4.61 × 10−7 mol2 l−2. The pressure coefficient yields a at 2°C of −43.8 cm3 atm−1. A single station where aragonite is present in the sediments gives a value of K′SPa = 9.2 × 10−7 (4°C, 81 atm). The calcite data are very similar to those determined experimentally by Ingle et al. (1973) for K′SPc at 2°C and 1 atm. The calculated is also indistinguishable from the experimental results of Ingle (1975) if is assumed to be independent of pressure.  相似文献   

19.
《Marine Chemistry》2001,75(3):229-248
Dissolved and particulate mercury and methylmercury concentrations were determined in the Southern Bight of the North Sea and the Scheldt estuary in the period 1991–1999. Mercury and methylmercury concentrations are higher before 1995 than after 1995, especially in the fluvial part.The North Sea: In the offshore stations, dissolved Hg concentrations are generally higher in winter than in summer while the reverse is true for particulate Hg KD values (KD=the concentration of particulate Hg (HgP in pmol kg−1) divided by the concentration of dissolved Hg (HgD in pmol l−1)) range from 100,000 to 1000,000 l kg−1. Dissolved methylmercury concentrations vary from 0.05 to 0.25 pmol l−1 in summer and from d.l. to 0.23 pmol l−1 in winter and particulate methylmercury concentrations from 1.8 to 36 pmol g−1 in summer and from 0.9 to 21 pmol g−1 in winter. The KD ranges from 9,000 to 219,000 l kg−1.The Scheldt estuary: In winter, dissolved Hg concentrations are elevated in the upper estuary, decrease exponentially in the low salinity range followed by a very slow decrease towards the mouth. In summer, they are low in the fluvial part, increase in the low salinity range or in the mid-estuary and sometimes show an increase in the lower estuary. Particulate Hg concentrations do not show any seasonal trend.Dissolved MMHg concentrations are much lower in winter, when maximum concentrations are found in the upper estuary, than in summer. In summer, the MMHg concentrations are low at low salinity, they show a first increase in the salinity range from 3 to 12, a decrease in the mid-estuary and a second increase in the lower estuary.The highest particulate MMHg concentrations are found in the upper estuary, while in the lower estuary generally lower and more constant values are observed. The ratio of dissolved MMHg to dissolved Hg (cruise averages between 1.3% and 20%), is higher than the ratio of particulate MMHg to particulate Hg (cruise averages of 0.27–0.90%). The KD values for MMHg are lower in the summer (30,000–65,000) than in autumn and winter (77,000–114,000).The Scheldt river: In the fluvial part of the Scheldt, dissolved increases in the most upstream stations, while particulate Hg shows no particular pattern. Dissolved MMHg ranges from 0.1 to 0.39 pmol l−1 and particulate MMHg from 3.1 to 43.5 pmol g−1. The MMHg concentrations are comparable to those found in the estuary and no seasonal variations could be observed.  相似文献   

20.
Measurements of bromoform (CHBr3), diiodomethane (CH2I2), chloroiodomethane (CH2ICl) and bromoiodomethane (CH2IBr) were made in the water column (5–100 m depth) of the Southern Ocean within 0–40 km of the Antarctic sea ice during the ANTXX1/2 transect of the German R/V Polarstern, at five locations between 70–72°S and 9–11°W in the Antarctic spring/summer of 2003–2004. Some of the profiles exhibited a very pronounced layer of surface sea-ice meltwater, as evidenced by salinity minima and temperature maxima, along with surface maxima in concentrations of CHBr3, CH2I2, CH2ICl and CH2IBr. These results are consistent with in situ surface halocarbon production by ice algae liberated from the sea ice, although production within the sea ice followed by transport cannot be entirely ruled out. Additional sub-surface maxima in halocarbons occurred between 20 and 80 m. At a station further from shore and not affected by surface sea-ice meltwater, surface concentrations of CH2I2 were decreased whereas CH2ICl concentrations were increased compared to the stations influenced by meltwater, consistent with photochemical conversion of CH2I2 to CH2ICl, perhaps during upward mixing from a layer at  70 m enhanced in iodocarbons. Mean surface (5–10 m) water concentrations of halocarbons in these coastal Antarctic waters were 57 pmol l− 1 CHBr3 (range 44–78 pmol l− 1), 4.2 pmol l− 1 CH2I2 (range 1.7–8.2 pmol l− 1), 0.8 pmol l− 1 CH2IBr (range 0.2–1.4 pmol l− 1), and 0.7 pmol l− 1 CH2ICl (range 0.2–2.4 pmol l− 1). Concurrent measurements in air suggested a sea-air flux of bromoform near the Antarctic coast of between 1 and 100 (mean 32.3, median 10.4) nmol m− 2 day− 1 and saturation anomalies of 557–1082% (mean 783%, median 733%), similar in magnitude to global shelf values. In surface samples affected by meltwater, CH2I2 fluxes ranged from 0.02 to 6.1 nmol m− 2 day− 1, with mean and median values of 1.9 and 1.1 nmol m− 2 day− 1, respectively.  相似文献   

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