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1.
Existence of gas-hydrate in the marine sediments elevates both the P- and S-wave seismic velocities, whereas even a small amount of underlying free-gas decreases the P-wave velocity considerably and the S-wave velocity remains almost unaffected. Study of both P- and S-wave seismic velocities or their ratio (VP/VS) for the hydrate-bearing sediment provides more information than that obtained by the P- or S-wave velocity alone for the quantitative assessment of gas-hydrate. We estimate the P- and S-wave seismic velocities across a BSR (interface between gas-hydrate and free-gas bearing sediments) using the travel time inversion followed by a constrained AVA modeling of multi channel seismic (MCS) data at two locations in the Makran accretionary prism. Using this VP/VS ratio, we then quantify the amount of gas-hydrate and free-gas based on two rock-physics models. The result shows an estimate of 12–14.5% gas-hydrate and 4.5–5.5% free-gas of the pore volume based on first model, and 13–20% gas-hydrate and 3–3.5% free-gas of the pore volume based on the second model, respectively.  相似文献   

2.
Dissolved and particulate trace metals (Cu, Cd, Pb, Zn, Ni, Fe and Mn) measured at six stations along the Scheldt estuary in October/November 1978 are compared with more recent data. Based on Ca content in the suspended matter, three distinct geochemical regions could be distinguished: the upper estuary (salinity 1–7) dominated by fluvial mud, mid-estuary (salinity 7–17) where the composition of the suspended matter remained relatively constant, and the lower estuary where marine mud prevailed. Re-suspension of sediments is the major factor controlling the composition of the particles in the upstream region. Anoxic conditions prevailed in the upper part of the estuary extending to a salinity of 15 in 1978, while at present the seaward boundary of the anoxic water body is located at less saline waters. Furthermore, the present-day metal load is much lower than in 1978. As a consequence of the changed situation, maxima in dissolved concentrations of redox-sensitive metals in the mid/lower estuary have moved as well, which affects the trace metal re-distribution pattern. In the anoxic zone, exchange processes between dissolved and particulate metal fractions were strongly redox regulated, with Fe and Mn as excellent examples. Iron was removed from the dissolved phase in the early stages of mixing resulting in an increase in the suspended particulate matter of the leachable ‘non-residual' Fe fraction from 2 to 3.5%. Due to its slower kinetics, removal of Mn from solution occurred in mid-estuary where oxygen concentrations increased. Cu, Cd and Zn on the contrary were mobilised from the suspended particles during estuarine mixing. External inputs of Pb, and to a lesser extent of Cu, in the lower estuary resulted in the increase of their particulate and the dissolved concentrations. Calculated Kd (distribution coefficient) values were used to assess the redistribution between the dissolved and particulate phase of the investigated metals. Due to the existence of the anoxic water body in the upper estuary, the importance of redox processes in determining the Kd values could be demonstrated. The sequence of Kd values in the upper estuary (Fe, Cd, Zn, Pb > Cu > Ni, Mn) is significantly different from that in the lower estuary (Fe > Mn > Pb, Ni, Zn, Cu, Cd). Thus, in such a dynamic estuary single metal-specific Kd values cannot be used to describe redistribution processes.  相似文献   

3.
The lipid composition was determined for 5 species of polychaete annelids collected by the Deep Submergence Vehicle ALVIN from high temperature chimneys at the 2500 m depth hydrothermal vent field of the East Pacific Rise. These are the first lipid biomarker analyses reported for these hydrothermal vent polychaetes. Lipid content was low in all samples (1.6–35.9 mg g–1 wet mass) and was dominated by polar lipid (78–90% of total lipid) with 8–19% sterol (ST), and very low storage lipid (triacylglycerol and wax ester). Total polyunsaturated fatty acids (PUFA) were moderately high (22–31% of total fatty acids (FA)) with extremely low or no docosahexaenoic acid (DHA, 22:6(n-3)). Eicosapentaenoic acid (EPA, 20:5(n-3)) levels were 5–6% in Alvinella pompejana and A. caudata and 10.3–13.7% in an errantiate polychaete (likely Hesionidae) and Hesiolyra bergii. There were greater PUFA and a greater EPA/AA (AA is arachidonic acid, 20:4(n-6)) ratio in the anterior versus the posterior half of A. pompejana, which may correlate to the strong temperature gradient reported in its tube. Total nonmethylene interrupted diunsaturated fatty acids (NMID) were 4–9% of total FA for most polychaete species and included several 20:2 and 22:2 components. The principal monounsaturated fatty acids (MUFA) included 18:1(n-7)c (14–19%), 16:1(n-7)c (2.6–10%) and 20:1(n-11)c (3–7% of total FA). These polychaete species may desaturate and elongate the bacterial-derived 18:1(n-7)c to obtain the essential FA EPA and AA. The major ST in the polychaetes is cholesterol (89–98% of total ST) with less cholesterol in the gut contents of A. pompejana. Other ST included 24-ethylcholesterol (1.5–5% of total ST) with lesser amounts of 24-methylenecholesterol, desmosterol, lathosterol, 24-methylcholesterol, 24-ethylcholesterol, and the stanols dehydrocholestanol and cholestanol. The high ST levels could play a role in thermal adaptation of membranes at the hydrothermal vent environment. Differences in the FA profiles separated the closely related species A. pompejana and A. caudata from Paralvinella grasslei, H. bergii, and the errantiate polychaete (likely Hesionidae).  相似文献   

4.
We analysed the alkenone unsaturation ratio (UK′37) in 87 surface sediment samples from the western South Atlantic (5°N–50°S) in order to evaluate its applicability as a paleotemperature tool for this part of the ocean. The measured UK′37 ratios were converted into temperature using the global core-top calibration of Müller et al. (1998) and compared with annual mean atlas sea-surface temperatures (SSTs) of overlying surface waters. The results reveal a close correspondence (<1.5°C) between atlas and alkenone temperatures for the Western Tropical Atlantic and the Brazil Current region north of 32°S, but deviating low alkenone temperatures by −2° to −6°C are found in the regions of the Brazil–Malvinas Confluence (35–39°S) and the Malvinas Current (41–48°S). From the oceanographic evidence these low UK′37 values cannot be explained by preferential alkenone production below the mixed layer or during the cold season. Higher nutrient availability and algal growth rates are also unlikely causes. Instead, our results imply that lateral displacement of suspended particles and sediments, caused by strong surface and bottom currents, benthic storms, and downslope processes is responsible for the deviating UK′37 temperatures. In this way, particles and sediments carrying a cold water UK′37 signal of coastal or southern origin are transported northward and offshore into areas with warmer surface waters. In the northern Argentine Basin the depth between displaced and unaffected sediments appears to coincide with the boundary between the northward flowing Lower Circumpolar Deep Water (LCDW) and the southward flowing North Atlantic Deep Water (NADW) at about 4000 m.  相似文献   

5.
Chemical profiles of both oxidized (nitrate and sulfate) and reduced (ammonium, sulfide, acid-volatile sulfide [AVS], and pyrite) materials and the corresponding distribution of denitrifier microbial communities were measured at low tide in sediments at Guandu in the estuary of the Tanshui River, northern Taiwan in August 2002. Denitrifier strains were isolated for physiological and phylogenic analyses. Based on the distribution of nitrogenous compounds and denitrifier abundances, the vertical profile of Guandu sediments could be separated into four layers: a mixed layer (the top 1 cm of depth, respectively containing 0.82–2.37 and 535.9–475.0 μM of nitrate and ammonium), a nitrate-concentrated layer (1–5 cm in depth, 2.37–0.53 and 475.0–1192.1 μM, respectively), a denitrifier-aggregation layer (5–7 cm in depth, 0.53–0.72 and 1192.1–1430.1 μM, respectively), and an ammonium-enriched layer (7–12 cm in depth, 0.72–0.78 and 1430.1–2196.6 μM, respectively). Denitrifier strains were detected in all layers except for the mixed layer. A variety of metabolic processes by these strains may occur in different layers. Bacillus jeotgali-, Bacillus sphaericus-, and Bacillus firmus-related strains isolated from the nitrate-concentrated layer may be involved in the nitrification-denitrification coupling process due to the relatively low nitrate concentrations (maximum = 2.37 μM), and may contribute to denitrification not nitrification. Bacillus bataviensis- and B. jeotgali-related strains isolated from the denitrifier-aggregation layer comprised the predominant denitrifier population (3.64 × 104 cells/g of denitrifier abundance). They possess the ability of dissimilatory nitrate reduction to ammonium (DNRA). Bacillus jeotgali-related strains and two newly identified strains of GD0705 and GD0706 isolated from the ammonium-enriched layer possibly use fermentative processes as the main metabolic pathway instead of denitrification when nitrate is scarce, and this further supports the high ammonium concentrations (up to 2.20 mM) found in the Guandu sediments. In addition, spore formation also enhances the chance of survival of these strains in the face with such a nitrate-deficient environment.  相似文献   

6.
Deep-sea sediment samples were collected in the Western Crozet Basin (Indian sector of the Southern Ocean) through Permanently Open Ocean Zone (POOZ), Polar Frontal Zone (PFZ) and Sub-Antarctic Zone (SAZ). Lipid class and fatty acid compositions were investigated to determine the sources and fate of organic matter in the first centimeter of sediment and, above this layer, in the fluff (when present) and particles in the overlying water. The total lipid content varied from 74 to 1033 μg l−1 in the overlying particles and fluffs, and from 24 to 97 μg g−1 dry mass (DM) in surficial sediments. Lipid composition was always dominated by phospholipids in the first centimeter of sediment and often in the overlying particles. The amount of phospholipids (labile compounds representative of fresh material) was compared to the amount of chlorophyll a (Chl a), another compound that is susceptible to rapid degradation. A strong N–S gradient was observed in the distribution of these two compounds, which was attributed to the contrasting hydrodynamic of the study area. The high sedimentation rate in POOZ resulted in better preservation of Chl a in this zone than in other zones of the Crozet Basin (PFZ and SAZ). Phospholipid fatty acids suggested the presence of viable as well as morphologically intact organisms, and these organisms consisted essentially of bacteria with some diatom cysts in the fluff of POOZ. These spores were able to grow in the culture, indicating that they were still viable. Despite the strong hydrodynamic variability, phospholipid fatty acids analysed from the deep-sea surficial sediments were never representative of plankton. This pointed to the extremely labile nature of the phospholipids originally present in planktonic material compared with Chl a, which was always found in overlying particles and surficial sediments.  相似文献   

7.
U–Th decay series isotopes, δ18O and Si measurements in the river estuarine waters and sediments of the polluted Hooghly estuary as well as the surface waters of the Bay of Bengal, its high salinity end member, are reported. Dissolved Si indicates that there are probably two mixing regimes, dissolved U behaviour is nonconservative and δ18O behaves conservatively in the overall estuarine region. Isotopes of reactive elements, viz. 234Th and 210Po, are removed from the estuarine waters in <2 days and <1 month, respectively, which is due to high suspended matter (30–301 mg l−1). 228Ra and 226Ra are profusely released into the estuarine waters in the low to mid-salinity regions.As expected, the opposite trend is observed in the case of estuarine sediments and suspended matter. Reactive isotopes of Th, 210Pb and 210Po are enriched, whereas Ra isotopes are depleted with respect to their parent nuclides in the estuarine sediments and suspended matter. 232Th/Al ratio appears well suited to study the distribution and mixing of the bed load sediments of the Ganga–Brahmaputra (G–B) and the Hooghly rivers with those from other rivers on the Bay of Bengal floor.  相似文献   

8.
The interplay between the oxygen minimum zone and remotely-forced oxygenation episodes determines the fate of the benthic subsystem off the Central Peruvian coast. We analyzed a 12 year monthly time-series of oceanographic and benthic parameters at 94 m depth off Callao, Central Peru (12°S), to analyze: (i) near-bottom oxygen level on the continental shelf in relation to dynamic height on the equator (095°W); and (ii) benthic ecosystem responses to oxygen change (macrobiotic infauna, meiofauna, and sulphide-oxidizing bacteria, Thioploca spp.). Shelf oxygenation episodes occurred after equatorial dynamic height increases one month before, consistent with the propagation of coastal trapped waves. Several but not all of these episodes occurred during El Niños. The benthic biota responded to oxygenation episodes by undergoing succession through three major ecological states. Under strong oxygen deficiency or anoxia, the sediments were nearly defaunated of macro-invertebrates and Thioploca was scarce, such that nematode biomass dominated the macro- and meiobiotas. When frequency of oxygenation events reduced the periods of anoxia, but the prevailing oxygen range was 10–20 μmol L−1, mats of Thioploca formed and dominated the biomass. Finally, with frequent and intense (>40 μmol L−1) oxygenation, the sediments were colonized by macrofauna, which then dominated biomass. The Thioploca state evolved during the 2002–2003 weak EN, while the macrofauna state was developed during the onset of the strong1997–1998 EN. Repeated episodes of strong oxygen deficiency during the summer of 2004, in parallel with the occurrence of red tides in surface waters, resulted in the collapse of Thioploca mats and development of the Nematode state. Ecological interactions may affect persistence or the transition between benthic ecosystem states.  相似文献   

9.
Coastal upwelling systems are regions with highly variable physical processes and very high rates of primary production and very little is known about the effect of these factors on the short-term variations of CO2 fugacity in seawater (fCO2w). This paper presents the effect of short-term variability (<1 week) of upwelling–downwelling events on CO2 fugacity in seawater (fCO2w), oxygen, temperature and salinity fields in the Ría de Vigo (a coastal upwelling ecosystem). The magnitude of fCO2w values is physically and biologically modulated and ranges from 285 μatm in July to 615 μatm in October. There is a sharp gradient in fCO2w between the inner and the outer zone of the Ría during almost all the sampling dates, with a landward increase in fCO2w.CO2 fluxes calculated from local wind speed and air–sea fCO2 differences indicate that the inner zone is a sink for atmospheric CO2 in December only (−0.30 mmol m−2 day−1). The middle zone absorbs CO2 in December and July (−0.05 and −0.27 mmol·m−2 day−1, respectively). The oceanic zone only emits CO2 in October (0.36 mmol·m−2 day−1) and absorbs at the highest rate in December (−1.53 mmol·m−2 day−1).  相似文献   

10.
Population structure and distribution of Terebralia palustris were compared with the environmental parameters within microhabitats in a monospecific stand of Avicennia marina in southern Mozambique. Stable carbon and nitrogen isotope analyses of T. palustris and potential food sources (leaves, pneumatophore epiphytes, and surface sediments) were examined to establish the feeding preferences of T. palustris. Stable isotope signatures of individuals of different size classes and from different microhabitats were compared with local food sources. Samples of surface sediments 2.5–10 m apart showed some variation (−21.2‰ to −23.0‰) in δ13C, probably due to different contributions from seagrasses, microalgae and mangrove leaves, while δ15N values varied between 8.7‰ and 15.8‰, indicating that there is a very high variability within a small-scale microcosm. Stable isotope signatures differed significantly between the T. palustris size classes and between individuals of the same size class, collected in different microhabitats. Results also suggested that smaller individuals feed on sediment, selecting mainly benthic microalgae, while larger individuals feed on sediment, epiphytes and mangrove leaves. Correlations were found between environmental parameters and gastropod population structure and distribution vs. the feeding preferences of individuals of different size classes and in different microhabitats. While organic content and the abundance of leaves were parameters that correlated best with the total density of gastropods (>85%), the abundance of pneumatophores and leaves, as well as grain size, correlated better with the gastropod size distribution (>65%). Young individuals (height < 3 cm) occur predominantly in microhabitats characterized by a low density of leaf litter and pneumatophores, reduced organic matter and larger grain size, these being characteristic of lower intertidal open areas that favour benthic microalgal growth. With increasing shell height, T. palustris individuals start occupying microhabitats nearer the mangrove trees characterized by large densities of pneumatophores and litter, as well as sediments of smaller grain size, leading to higher organic matter availability in the sediment.  相似文献   

11.
Urban stormwater runoff could contribute to the deterioration of water quality of a receiving water body. In this research, field studies and laboratory experiments were conducted to assess the microbial contamination resulting from urban stormwater runoff into the Lake Pontchartrain estuary. Fecal coliform, Escherichia coli and enterococci were used as indicator organisms. The specific objectives of the research were to examine the distribution of the indicator organisms in different environmental elements (water column, suspended particles and sediment) and to further investigate the mechanisms related to their fate. Results of the research indicated satisfactory water quality at the study sites during dry weather periods. However, a significant increase was observed in the concentrations of the indicator organisms in the water columns and sediment at specific study sites following a given stormwater event. Three to seven days were needed for the elevated indicator organisms to return back to their background levels in the water column and sediment, respectively. The mechanism of sedimentation contributed to a reduction in the microbial concentration in the water column, as the indicator organisms were found to attach to the suspended particles in the stormwater. The percentage of fecal coliform, E. coli and enterococci attached to the suspended particles was found to be within the range of 9.8–27.5%, 21.8–30.4%, and 8.4–11.5% of the total indicator organisms in the stormwater loaded into the estuary, respectively. About 75–80% of the total indicator organisms remained free-floating for some distance in the water column before dying off.  相似文献   

12.
The clam Scrobicularia plana and the polychaete worm Nereis diversicolor were collected in several sites from a littoral enclosure in SW Spain. The aim of our study was to relate various biomarker responses in these species to a pollution gradient caused by untreated domestic discharges and to verify the adequacy of the selected species as sentinels in this habitat. The biomarkers selected were the antioxidant enzymes catalase (CAT), glutathione peroxidase (GPX) and DT-diaphorase (DT-D). In addition, the activities of cytochrome P450-dependent ethoxyresorufin O-deethylase (EROD) activity, the phase II detoxifying enzyme glutathione S-transferase (GST) and the neurotoxicity marker acetylcholinesterase (AChE) were measured. Metallothionein levels were selected as biomarkers of heavy metals exposure in both species. The results suggest a different response in the water filtering organism (clam) and the sediment eater (polychaete), probably as a consequent of different pollution exposure and that samples from the “Caño Sancti-Petri” were exposed to biologically active compounds that altered some of their biochemical responses. AChE was the most sensitive biomarker in both species and N. diversicolor proved to be a more robust sentinel in this ecosystem.  相似文献   

13.
We report several biogeochemical parameters (dissolved inorganic carbon (DIC), total alkalinity (TA), dissolved oxygen (DO), phosphate (PO4), nitrate + nitrite (NO3 + NO2), silicate (Si(OH)4)) in a region off Otaru coast in Hokkaido, Japan on a “weekly” basis during the period of April 2002–May 2003. To better understand the long-term temporal variations of the main factors affecting CO2 flux in this coastal region and its role as a sink/source of atmospheric CO2, we constructed an algorithm of DIC and TA using other hydrographic properties. We estimated the CO2 flux across the air–sea interface by using the classical bulk method. During 1998–2003 in our study region, the estimated fCO2sea ranged about 185–335 μatm. The maximum of fCO2sea in the summer was primarily due to the change of water temperature. The minimum of fCO2sea in the early spring can be explained not only by the change of water temperature but also the change of nutrients and chlorophyll-a. To clarify the factors affecting fCO2sea (water temperature, salinity, and biological activity), we carried out a sensitivity analysis of these effects on the variation of fCO2sea. In spring, the biological effect had the largest effect for the minimum of fCO2sea (40%). In summer, the water temperature effect had the largest effect for the maximum of fCO2sea (25%). In fall, the water temperature effect had the largest effect for the minimum of fCO2sea (53%). In winter, the biological effect had the largest effect for the minimum of fCO2sea (35%).We found that our study region was a sink region of CO2 throughout a year (−0.78 mol/m2/yr). Furthermore, we estimated that the increase of fCO2sea was about 0.56 μatm/yr under equilibrium with the atmospheric CO2 content for the period 1998–2003, with the temporal changes in the variables (T, S, PO4) on fCO2sea, thus as the maximum trend of each variable on fCO2sea was 0.22 μatm/yr, and the trend of residual fCO2 including gas exchange was 0.34 μatm/yr. This result suggests that interaction among variables would affect gas exchange between air and sea effects on fCO2sea. We conclude that this study region as a representative coastal region of marginal seas of the North Pacific is special because it was measured, but there is no particular significance in comparison to any other area.  相似文献   

14.
The net uptake of inorganic carbon and nitrogen, phosphate and silicate and the net production of dissolved oxygen and organic carbon, nitrogen and phosphorus have been examined in the Ría de Arousa, a large coastal embayment in the NW Iberian upwelling system. Fluxes and net budgets were estimated with a non-stationary 2-D box model [Rosón, G., Álvarez-Salgado, X.A., Pérez, F.F., 1997. A non-stationary box-model to determine residual flows in a partially mixed estuary, based on both thermoline properties. Application to the Ría de Arousa (NW Spain). Estuarine, Coastal Shelf Sci., 44, 249–262] and the distributions of the different species acquired twice a week between May and October 1989 [Rosón, G., Pérez, F.F., Álvarez-Salgado, X.A., Figueiras, F.G., 1995. Variation of both thermohaline and chemical properties in an estuarine upwelling ecosystem: Ría de Arousa: 1. Time Evolution. Estuarine, Coastal Shelf Sci., 41, 195–213]. High N/P and N/Si net uptake ratios of 21 and 3.2 were observed during the upwelling season. The rapid recycling of phosphorus compared to nitrogen and the recurrent succession from pioneer diatoms (Si/N1) to red-tide forming species (Si/N=0) following the periodic upwelling pulses are the reasons behind the observed ratios. The molar ratios of dissolved oxygen production to inorganic carbon (−1.48) and nitrogen uptake (−10.2) during the upwelling season agree with the Redfield stoichiometry. On the contrary, net nutrient regeneration occurred with N/P, N/Si and O2/C ratios of 7.4, 1.0 and −1.02 during an intense autumn downwelling event. These low ratios are due to the release of an excess of phosphate, silicate and CO2 from the sediments. Conversely, the production of inorganic nitrogen is associated to the consumption of dissolved oxygen following a Redfield ratio of −10.0. Whereas the C/N ratio of the suspended organic matter produced during the upwelling season and consumed during the autumn downwelling event is 6.3–6.7, the N/P ratio changes from 11 during the upwelling season to 15 during the autumn downwelling. About 1/5 of the dissolved oxygen produced during the upwelling season and consumed during the autumn downwelling is delivered to and came from the atmosphere, respectively. Despite the C/N/P/O2 ratios differ from the Redfield values, the high correlation between nutrient salts consumption and dissolved oxygen production (r2=0.74–0.86) allow to estimate an average net ecosystem production (NEP) from the individual elements. The 3–4 d time-scale variability of the average NEP depends on the 2-week periodicity of upwelling pulses, the heat exchange across the sea surface and the stability of the water column. As much as 70% of the total variability can be explained with a linear combination of these parameters.  相似文献   

15.
Woei-Lih Jeng   《Marine Chemistry》2006,102(3-4):242-251
The n-alkane average chain length (ACL) is the weight-averaged number of carbon atoms of the higher plant C25–C33 n-alkanes. The abundance of individual n-alkanes from higher plant sources generally increases with increasing carbon number in coastal marine sediments around Taiwan, but this trend is reversed for petrogenic hydrocarbons. The ACL would potentially be lowered if petrogenic hydrocarbons were added to sediments containing biogenic hydrocarbons alone. To test this idea, a marine environment off southwestern Taiwan known to contain both biogenic and petrogenic hydrocarbons and two nearby rivers were selected for investigating possible difference in ACL values between their sediments. The average CPI of C25–C33 n-alkanes was 4.08 ± 2.04 (range 1.90–8.96, n = 15) for the river sediments and 1.70 ± 0.16 (range 1.43–1.97, n = 15) for the marine sediments. The ACL of C25–C33 n-alkanes for river sediments ranged from 29.2 to 30.5 (average 29.9 ± 0.4), and for marine sediments from 28.4 to 29.3 (average 28.9 ± 0.3). The ACL difference between marine and river sediments was significant (Student's t test at 99% confidence) although it appeared small. It is suggested that the ACL can be an additional indicator for detection of petrogenic hydrocarbons in coastal marine sediments.  相似文献   

16.
Diel changes in vertical distribution and gut pigment contents of Acartia clausi andPseudodiaptomus hessei were studied during several 24-h time series performed between 1993 and 1997 in four sites of the Ebrié Lagoon (Côte d'Ivoire). The sites differed by their morphology and their hydrological structure and by the vertical distribution of chlorophyll biomass. Both species showed classical diel vertical migrations (DVM). Copepodites and adult stages of P. hessei were almost benthic during the day and evenly distributed through the water column at night. The amplitude of DVM of A. clausi increased from copepodites I–III to adults. Copepodites and adults of A. clausi increased significantly their gut fluorescence at night, whereas those of P. hessei showed no clear diel feeding rhythm (DFR). These results suggest that A. clausi feed mostly at night on phytoplanktonic particles and P. hessei feed mostly on benthic algal particles during the day and on sestonic particles at night. No relationship was observed between DFR and DVM because both patterns occurred when food was either vertically homogeneous or vertically stratified. The daily average gut fluorescence of A. clausi increased with ambient chlorophyll concentration until around 12–15 μg l−1, whereas no relationship was found for P. hessei. The implication of these patterns on the adaptation capacities and the behaviour of the two species are discussed. The DVM of P. hessei should explain its rarity in the estuarine area. The comparison of our results with previous ones suggests an evolution of A. clausi DFR between 1981–1982 and 1996–1997, in relation to an intensification of eutrophication.  相似文献   

17.
Laboratory and in situ experiments were performed to assess the use of bromide as a tracer forin situ studies of benthic solute exchange. Bromide was used in the benthic chamber lander ‘ Elinor ’ for flux measurements in coastal sediments of the German Bight, Kiel Bight and Skagerrak (28–700 m water depth). Tracer and total oxygen uptake were monitored simultaneously in the same chamber incubation. Concurrently, in situ oxygen micro-profiles were recorded at the same locations by the profiling lander ‘ Profilur ’. Deployment in an anoxic silt (Kiel Bight) confirmed that in the absence of bioturbation and advection, tracer transport into the sediment was driven solely by molecular diffusion. This flux could be well described by a simple box model accounting for molecular diffusion only. In oxic sediments (German Bight and Skagerrak) enhanced exchange of bromide tracer due to bioirrigation parallelled enhanced oxygen uptake equivalent to a 4-fold molecular diffusive flux. Our experiments showed that incubations can be short. Depending on irrigation activity of the fauna, however, incubation length should exceed 3 h in order to provide a useful data base for flux calculations. The method demonstrating caveats is discussed and indicate possible improvements. The results show how the bromide tracer addition can be used as a tool for determining solute fluxes exceeding diffusive flux in benthic chamber incubations.  相似文献   

18.
Biochemical characterization of cholinesterase activity (ChE) was carried out on the Antarctic scallop Adamussium colbecki collected in winter 2000 from Campo Icaro (Ross Sea, Antarctica) in order to increase its suitability as a sentinel organism for monitoring the Antarctic environment. The digestive gland, gills and adductor muscle were investigated for substrate specificity and inhibitors sensitivity using acetylthiocholine iodide (ASCh) and butyrylthiocholine iodide (BSCh) as substrates and tetra (monoisopropyl)pyrophosphor-tetramide (Iso-OMPA), 1,5-bis(4-allyldimethylammoniumphenyl)-penthan-3-one dibromide (BW284c51) and the insecticide chlorpyrifos as inhibitors. Effect of in vivo exposure to ZnCl2 was also investigated. All the tissues expressed ChE activity (gill > adductor muscle > digestive gland) and low substrates specificity throughout the hydrolysis of both ASCh and BSCh substrates. Partial (25–29%) and total inhibition (100%) of ChE activity in gills was demonstrated following in vitro incubation with Iso-OMPA and BW284c51 (3 mM), respectively. Concentration-dependent inhibition was also evident with chlorpyrifos in the range 10−4–10−10 M (IC50 10−6) while in vivo exposure to ZnCl2 did not seem to affect ChE activity in the scallop. The potential use of ChE in the A. colbecki as biomarker for monitoring water contamination in the marine Antarctic environment is discussed.  相似文献   

19.
The short-term (5 day) accumulation of Cu and Zn in different tissues of the marine gastropod, Littorina littorea, has been studied in the presence of 10 mg l−1 of antifouling paint particles and pre- or simultaneously contaminated algal food (Ulva lactuca). Accumulation of Cu was observed in the head–foot, digestive gland–gonad complex and gills to extents dependent on how and when food was contaminated and administered. However, retention of Zn was only observed in the gills and only when L. littorea and U. lactuca were simultaneously exposed to paint particles. Relative to the alga, faecal material was highly enriched in Zn, suggesting that the animal is able to rapidly eliminate this metal, most likely through the formation and egestion of insoluble phosphate granules. Thus, L. littorea is a useful biomonitor of marine contamination by antifouling applications in respect of Cu but not Zn.  相似文献   

20.
An improved model is presented for the calculation of the solubility of carbon dioxide in aqueous solutions containing Na+, K+, Ca2+, Mg2+, Cl−, and SO42− in a wide temperature–pressure–ionic strength range (from 273 to 533 K, from 0 to 2000 bar, and from 0 to 4.5 molality of salts) with experimental accuracy. The improvements over the previous model [Duan, Z. and Sun, R., 2003. An improved model calculating CO2 solubility in pure water and aqueous NaCl solutions from 273 to 533K and from 0 to 2000 bar. Chemical Geology, 193: 257–271] include: (1) By developing a non-iterative equation to replace the original equation of state in the calculation of CO2 fugacity coefficients, the new model is at least twenty times computationally faster and can be easily adapted to numerical reaction-flow simulator for such applications as CO2 sequestration and (2) By fitting to the new solubility data, the new model improved the accuracy below 288 K from 6% to about 3% of uncertainty but still retains the high accuracy of the original model above 288 K. We comprehensively evaluate all experimental CO2 solubility data. Compared with these data, this model not only reproduces all the reliable data used for the parameterization but also predicts the data that were not used in the parameterization. In order to facilitate the application to CO2 sequestration, we also predicted CO2 solubility in seawater at two-phase coexistence (vapor–liquid or liquid–liquid) and at three-phase coexistence (CO2 hydrate–liquid water–vapor CO2 [or liquid CO2]). The improved model is programmed and can be downloaded from the website http://www.geochem-model.org/programs.htm.  相似文献   

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