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1.
The spatial and temporal dynamics of dissolved inorganic nitrogen, dissolved phosphate, dissolved silica and chlorophyll a were measured seasonally at eight stations in the Ria de Aveiro. Between December 2000 and September 2001, the seasonal succession of phytoplankton assemblages, inferred after the spatial and seasonal variation of silica and of chlorophyll a concentrations, showed that diatoms (μmol Si L−1) dominated from late autumn until early spring, while chlorophytes (μg Chl a L−1) bloomed during late spring and summer. The Si:N:P ratios and Si concentrations indicated no seasonal depletion in dissolved silica, as in other temperate systems, possibly because of abnormal precipitation and flood events prolonging the supply of dissolved Si to the system. The Si:N:P ratios suggested P limitation at the system level. Despite the relative proportions of available nutrients, the mean phosphorus concentration (5.3 μmol L−1) was above the reported half-saturation constants for P uptake by phytoplankton. Thus, in Ria de Aveiro, the seasonal succession of phytoplankton assemblages may also be dependent on the grazing capacity of the pelagic community through top-down regulation.  相似文献   

2.
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   

3.
The suspension-feeding gastropod Crepipatella dilatata occurs in estuaries in southern Chile that experience considerable fluctuations in salinity, driven by tidal and atmospheric forces. In the Quempillén estuary salinities as low as 9 psu may occur after severe rainstorms, and persist for several hours. In this study salinity was the major factor influencing the clearance rate of C. dilatata. At salinities below 20 psu, filtration ceased, whereas at high salinities (>22 psu) mean clearance rate was 0.24 l h−1 standard animal−1 (S.D. 0.18) for actively filtering individuals. This was confirmed by laboratory experiments under controlled conditions. Endoscopic observations were consistent with measurements of clearance rate, and showed that at salinity 25–30 psu the rate of transport along the gill filaments of particulate material embedded in mucus was 759 μm s−1 (S.D. 480), but particle transport ceased at and below salinity 20 psu. Complete or partial isolation of the mantle cavity from the environment may be a mechanism to protect soft tissues and/or incubated egg capsules from osmotic stress.  相似文献   

4.
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   

5.
The spawning habitat of Emmelichthys nitidus (Emmelichthyidae) in south-eastern Australia is described from vertical ichthyoplankton samples collected along the shelf region off eastern through to south-western Tasmania during peak spawning in October 2005–06. Surveys covered eastern waters in 2005 (38.8–43.5°S), and both eastern and southern waters in 2006 (40.5°S around to 43.5°S off the south-west). Eggs (n = 10,393) and larvae (n = 378) occurred along eastern Tasmania in both years but were rare along southern waters south and westwards of 43.5°S in 2006. Peak egg abundances (1950–2640 per m−2) were obtained off north-eastern Tasmania (40.5–41.5°S) between the shelf break and 2.5 nm inshore from the break. Eggs were up to 5-days old, while nearly 95% of larvae were at the early preflexion stage, i.e. close to newly emerged. Average abundances of aged eggs pooled across each survey declined steadily from day-1 to day-5 eggs both in 2005 (97-18) and 2006 (175-34). Moreover, day-1 egg abundances were significantly greater 2.5 nm at either side of the break, including at the break, than in waters ≥5 nm both inshore and offshore from the break. These results, complemented with egg and larval data obtained in shelf waters off New South Wales (NSW; 35.0–37.7°S) in October 2002–03, indicate that the main spawning area of E. nitidus in south-eastern Australia lies between 35.5°S off southern NSW and 43.5°S off south-eastern Tasmania, and that spawning activity declines abruptly south and westwards of 43.5°S around to the south-west coast. In addition, quotient analyses of day-1 egg abundances point to a preferred spawning habitat contained predominantly within a 5 nm corridor along the shelf break, where waters are 125–325 m deep and median temperatures 13.5–14.0 °C. Spawning off eastern Tasmania is timed with the productivity outburst typical of the region during the austral spring, and the temperature increase from the mixing between the southwards advancing, warm East Australian Current and cooler subantarctic water over the shelf. Overall, ichthyoplankton data, coupled with reproductive information from adults trawled off Tasmania, indicate that E. nitidus constitutes a suitable species for the application of the daily egg production method (DEPM) to estimate spawning biomass. This finding, together with evidence in support of a discrete eastern spawning stock extending from southern NSW to southern Tasmania, strengthens the need for DEPM-based biomass estimates of E. nitidus prior to further fishery expansion.  相似文献   

6.
Axenic cultures of the microalgae species, Dunaliella tertiolecta and Phaeodactylum tricornutum were grown at arsenic (As) concentrations typically found in uncontaminated marine environments ( 2 µg L− 1) under different phosphorus concentrations. D. tertiolecta accumulated higher arsenic concentrations (mean: 13.7 ± 0.7 µg g− 1 dry mass) than P. tricornutum (mean: 1.9 ± 0.2 µg g−1 dry mass). Media phosphorus concentrations (0.6–3 mg/L) had little influence on microalgae growth rates or arsenic accumulation. Arsenic was present as lipid bound (29–38%; 4.2–9.5%), water-soluble (20–29%; 26–34%) and residue bound (41–45%; 57–69%) arsenic species in D. tertiolecta and P. tricornutum respectively. Hydrolysed lipids contained mostly glycerol arsenoribose (OH- ribose), dimethylarsinate (DMA) and inorganic arsenic (As(V)) moieties. Water-soluble species of microalgae were very different. D. tertiolecta contained inorganic arsenic (54–86%) with variable amounts of DMA (7.4–20%), arsenoriboses (5–25%) and traces of methylarsonate (MA) ( 1%). P. tricornutum contained mostly DMA (32–56%) and phosphate arsenoribose (PO4-ribose, 23–49%) and small amounts of OH-ribose (3.8–6.5%) and As(V) (9–16%). Both microalgae contained an unknown cationic arsenic species. The residue fractions of both microalgae contained predominately inorganic arsenic (99–100%). These results show that at natural seawater arsenic concentrations, both algae take up substantial amounts of inorganic arsenic that is complexed with structural elements or sequestered in vacuoles as stable complexes. A significant portion is also incorporated into lipids. Arsenic is metabolised to simple methylated species and arsenoriboses.  相似文献   

7.
Industrial activities, notably oil and gas industries, are expanding in the Arctic. Most of the biomarkers were developed using temperate organisms living at temperatures above 10 °C. Little is known about the biomarker responses of organisms living between −1.88 and 5 °C. Therefore, assessment of the toxicity of chemicals to cold-water adapted species is required. In this study, the Arctic scallop, Chlamys islandicus, was selected as a key species for bio-monitoring because of wide distribution in Arctic waters and its commercial value. Test animals, stored in seawater at 2 °C, were injected with benzo(a)pyrene (diluted in cod liver oil 5 mg ml−1) in the adductor muscle every 24 h for four days giving a final dose of 0, 74 and 90.6 mg kg−1 wet weight for control, low and high dose, respectively. The biomarkers used were total oxyradical scavenging capacity (TOSC) in the digestive gland and cell membrane stability of haemocytes. TOSC values were significantly reduced (ca. 30%) in exposed groups (P<0.05), indicating a depletion in oxyradical molecular scavengers. The antioxidant defences appeared to be overwhelmed by the reactive oxygen species as the plasma membranes of haemocytes were destabilised (P<0.05) probably due to lipid peroxidation. These data indicate that reactive oxygen species (ROS) were produced by Arctic scallops via the metabolisation of benzo(a)pyrene at 2 °C.  相似文献   

8.
We proposed an empirical equation of sea surface dimethylsulfide (DMS, nM) using sea surface temperature (SST, K), sea surface nitrate (SSN, μM) and latitude (L, °N) to reconstruct the sea surface flux of DMS over the North Pacific between 25°N and 55°N: ln DMS = 0.06346 · SST − 0.1210 · SSN − 14.11 · cos(L) − 6.278 (R2 = 0.63, p < 0.0001). Applying our algorithm to climatological hydrographic data in the North Pacific, we reconstructed the climatological distributions of DMS and its flux between 25 °N and 55 °N. DMS generally increased eastward and northward, and DMS in the northeastern region became to 2–5 times as large as that in the southwestern region. DMS in the later half of the year was 2–4 times as large as that in the first half of the year. Moreover, applying our algorithm to hydrographic time series datasets in the western North Pacific from 1971 to 2000, we found that DMS in the last three decades has shown linear increasing trends of 0.03 ± 0.01 nM year− 1 in the subpolar region, and 0.01 ± 0.001 nM year− 1 in the subtropical region, indicating that the annual flux of DMS from sea to air has increased by 1.9–4.8 μmol m− 2 year− 1. The linear increase was consistent with the annual rate of increase of 1% of the climatological averaged flux in the western North Pacific in the last three decades.  相似文献   

9.
The bioavailability and bacterial degradation rates of dissolved organic matter (DOM) were determined over a seasonal cycle in Loch Creran (Scotland) by measuring the decrease in dissolved organic carbon (DOC), nitrogen (DON) and phosphorous (DOP) concentrations during long-term laboratory incubations (150 days) at a constant temperature of 14 °C. The experiments showed that bioavailable DOC (BDOC) accounted for 29 ± 11% of DOC (average ± SD), bioavailable DON (BDON) for 52 ± 11% of DON and bioavailable DOP (BDOP) for 88 ± 8% of DOP. The seasonal variations in DOM concentrations were mainly due to the bioavailable fraction. BDOP was degraded at a rate of 12 ± 4% d– 1 (average ± SD) while the degradation rates of BDOC and BDON were 7 ± 2% d– 1 and 9 ± 2% d– 1 respectively, indicating a preferential mineralization of DOP relative to DON and of DON relative to DOC. Positive correlations between concentration and degradation rate of DOM suggested that the higher the concentration the faster DOM would be degraded. On average, 77 ± 9% of BDOP, 62 ± 14% of BDON and 49 ± 19% of BDOC were mineralized during the residence time of water in Loch Creran, showing that this coastal area exported C-rich DOM to the adjacent Firth of Lorne. Four additional degradation experiments testing the effect of varying temperature on bioavailability and degradation rates of DOM were also conducted throughout the seasonal cycle (summer, autumn, winter and spring). Apart from the standard incubations at 14 °C, additional studies at 8 °C and 18 °C were also conducted. Bioavailability did not change with temperature, but degradation rates were stimulated by increased temperature, with a Q10 of 2.6 ± 1.1 for DOC and 2.5 ± 0.7 for DON (average ± SD).  相似文献   

10.
Transparent exopolymer particles (TEP) are formed by the assembly of dissolved precursors, mainly mono and polysaccharides (DMCHO and DPCHO) that are released by microorganisms. Although TEP formation plays a significant role in carbon export to deep waters and can affect gas exchange at the sea surface, simultaneous measurements of TEP and their precursors in natural waters have been scantly reported. In this study, we described the spatial (vertical and regional) distribution of TEP, DMCHO and DPCHO in a region located around the Antarctic Peninsula, assessed their contribution to the total organic carbon pool, and explored their relationships with phytoplankton (with chlorophyll a (chl a) as a proxy) and bacteria. TEP concentration ranged from undetectable values to 48.9 µg XG eq L− 1 with a mean value of 15.4 µg XG eq L− 1 (11.6 µg TEP-C L− 1). DMCHO and DPCHO showed average values of 4.3 µmol C L− 1 and 8.6 µmol C L− 1, respectively. We did not find simple relationships between the concentrations of TEP and dissolved carbohydrates, but a negative correlation between DMCHO and DPCHO was observed. Chl a was the best regressor of TEP concentration in waters within the upper mixed layer, while bacterial production was the best regressor of TEP concentration below the mixed layer, underlining the direct link between these particles and bacterial activity in deep waters.  相似文献   

11.
Diopatra neapolitana Delle Chiaje, 1841 (Annelida, Onuphidae) is an important economic natural resource in Ria de Aveiro (northwestern coast of Portugal) and throughout Europe. The species is intensively harvested for use as fresh bait. However, there is only limited knowledge about its life cycle derived from a previous study in Mediterranean Sea. Reproduction and development patterns are known to vary biogeographically, making it important to base management decisions on locally appropriate information. This work examines reproduction patterns for populations from the Eastern Atlantic, which have not previously been assessed, with an eye towards drawing Atlantic–Mediterranean comparisons and informing local management strategies. The study was conducted from May 2007 to April 2009 in Ria de Aveiro. The reproductive biology of D. neapolitana was described from the proportional variation of worms with gametes in the coelom and from the progression of the oocyte diameter. Individuals with gametes inside the coelom were found all year round, but the peak reproductive period occurred between May and August, when almost all individuals had gametes in the coelom and females contained more oocytes than at any other time of the year. The overall male:female ratio was close to 1:1 and the oocyte diameter ranged from 40 to 240 μm. In vitro fertilization was performed and the results compared to other studies. Based on the present results, some protection measures are suggested to implement a sustainable exploitation of the species.  相似文献   

12.
Mercury accumulation throughout the lifespan of Liza aurata (Risso, 1810) was analysed in four tissues (muscle, gills, liver and brain) in two southern European coastal ecosystems with distinct mercury contamination. Specimens from four to five age classes were captured in two sampling sites in the Ria de Aveiro (Laranjo bay and Mira), a system historically contaminated by industrial mercury, and in one site in the Mondego estuary, assumed as a mercury-free ecosystem. Mercury concentration in all tissues was found to be significantly higher in the Ria de Aveiro (Laranjo bay) compared to the Mondego, in accordance with the environmental contamination (water, sediments and suspended particulate matter). Significant differences inside the Ria de Aveiro (between the Mira and Laranjo bay) were only detected in the liver. This tissue registered the highest levels of mercury (ranging from 0.11 to 4.2 μg g−1) in all sampling sites, followed by muscle, brain, and gills. In all sampling sites and tissues was denoted a mercury dilution pattern along the lifecycle (except in liver at the Mondego, the reference area where the concentrations are always very low). An exponential trend was found in the metal age variation patterns in Laranjo (the most contaminated area) and a linear trend in the Mira and the Mondego (the least contaminated areas). Organic mercury concentration in muscle generally accounted for over 95% of total mercury concentration, and followed the same accumulation pattern of total mercury. This fish species is of lesser importance in mercury transfer to adjacent coastal areas and although the consumption of fish from Laranjo may present some risk for the humans, this risk decreases with fish age/size.  相似文献   

13.
The absorption of anthropogenic CO2 and atmospheric deposition of acidity can both contribute to the acidification of the global ocean. Rainfall pH measurements and chemical compositions monitored on the island of Bermuda since 1980, and a long-term seawater CO2 time-series (1983–2005) in the subtropical North Atlantic Ocean near Bermuda were used to evaluate the influence of acidic deposition on the acidification of oligotrophic waters of the North Atlantic Ocean and coastal waters of the coral reef ecosystem of Bermuda. Since the early 1980's, the average annual wet deposition of acidity at Bermuda was 15 ± 14 mmol m− 2 year− 1, while surface seawater pH decreased by 0.0017 ± 0.0001 pH units each year. The gradual acidification of subtropical gyre waters was primarily due to uptake of anthropogenic CO2. We estimate that direct atmospheric acid deposition contributed 2% to the acidification of surface waters in the subtropical North Atlantic Ocean, although this value likely represents an upper limit. Acidifying deposition had negligible influence on seawater CO2 chemistry of the Bermuda coral reef, with no evident impact on hard coral calcification.  相似文献   

14.
Successful reproduction by scleractinian corals is essential for the maintenance of populations that form the foundation of coral reef ecosystems. Laboratory experiments were done to determine the effects of reduced salinity on the fertilization success and larval survival of two coral species, Platygyra daedalea and Acropora millepora, from the Great Barrier Reef, Australia. Fertilization rates of P. daedalea and A. millepora were significantly reduced at 25.8 psu and 33.1 psu, respectively, and completed blocked at 18.4 psu for A. millepora. The estimated larval survival times were similar from 36.8 to 25.8 psu (P. daedalea 291–312 h, A. millepora 207–264 h), whereas the 18.4 psu treatment resulted in estimates of 153 h and 24 h for P. daedalea and A. millepora, respectively. These results demonstrate that reduced salinity is detrimental to the reproductive success of these corals, and if salinity is lowered by natural or anthropogenic sources during spawning, this would lead to decreased reproductive success and recruitment on reefs.  相似文献   

15.
The euryhaline polychaete Marenzelleria viridis is a notorious invader of the Baltic region and while many studies have focused on the effects of osmotic stress on larval development of the species, few have assessed its effect on adult specimens. This study investigated the effects of low salinity on the physiology of M. viridis by using its regenerative capacity as a proxy for physiologic performance. Specimens were collected in spring 2015 on sandy flats in Hempstead Bay (Long Island, New York), a site that falls within its native range. Worms were ablated between the 14th and 20th chaetigers and cultured at five different salinity treatments (24psu, 15psu, 10psu, 5psu and 0psu) that reflected the broad salinity regimes of its distributional range. Data for anterior regeneration were analysed and presented. Morphogenesis during anterior regeneration was characterized by the formation of a blastema from which the major anatomic structures emerged. All specimens cultured at 5–24psu successfully completed regeneration whereas 75% of specimens cultured at 0psu died and the survivors were unable to proceed beyond the blastema stage. Salinity did not have an effect on regeneration time (14.5–15.1 days) but did have an effect on the percentage of chaetigers regenerated (lowest – 77% at 5psu, highest – 97.5% at 15‰). The post‐regeneration phase was characterized by variability in pigmentation patterns in the regenerated anterior structures, which appear to be independent of salinity treatments. In conclusion, adult M. viridis appears to exhibit high tolerance to low salinity environments, which may have been inherited from its larval stages. In addition, the different pigmentation patterns observed in regenerated structures may allude to the variability of this feature in spionids.  相似文献   

16.
Four behaviours of mature Aurelia labiata medusae (Scyphozoa) were observed. Touching the manubrium with a soft, hollow, silicone rubber ball or a foam rubber ball caused medusae at a depth of 1 m to swim to the surface. Dense aggregations of medusae did not form within 5 m of rock walls. Medusae did not swim into water with salinity < 20 parts per thousand. Sunlight-stimulated directional swimming was to the west. These behaviours add to a growing list of adaptive behaviours of Aurelia labiata medusae.  相似文献   

17.
《Oceanologica Acta》1999,22(5):473-485
The hydrological features of Ria de Aveiro, a coastal lagoon on the northwest Atlantic coast of Portugal, were investigated in two sampling surveys carried out between 3/6 and 24/6/97 and between 29/6 and 7/7/97, respectively. There was a significant freshwater inflow into the lagoon during the first survey, especially in the first days, due to the recent rainfalls. Records concerning water level, salinity, temperature and current velocity were performed at several stations located along the four main channels of the lagoon. The type of tide at the mouth was determined and was observed that astronomical tide is the main forcing agent driving water circulation in Ria de Aveiro. The tide at the mouth is semidiurnal and the tidal wave propagation in the lagoon has the characteristics of a damped progressive wave. Typical estuarine longitudinal salinity and temperature gradients connected with the distance to the mouth were identified, whereas vertical and transverse gradients were found unimportant, except in the frontal zone between oceanic and fresh water masses. According to the results, even though Ria de Aveiro should be considered as vertically homogeneous, some channels may reveal characteristics of a partially mixed estuary, depending on the freshwater input.  相似文献   

18.
Iron chemistry in seawater has been extensively studied in the laboratory, mostly in small-volume sample bottles. However, little has been reported about iron wall sorption in these bottles. In this paper, radio-iron 55Fe was used to assess iron wall adsorption, both in terms of capacity, affinity and kinetics. Various bottle materials were tested. Iron sorption increased from polyethylene/polycarbonate to polymethylmetacrylate (PMMA)/high-density polyethylene/polytetrafluoroethylene to glass/quartz, reaching equilibrium in a 25–70 h period. PMMA was studied in more detail: ferric iron (Fe(III)) adsorbed on the walls of the bottles, whereas ferrous iron (Fe(II)) did not. Considering that in seawater the inorganic iron pool mostly consists of ferric iron, the wall will be a factor that needs to be considered in bottle experiments.The present data indicate that for PMMA with specific surface (S)-to-volume (V) ratio S/V, both iron capacity (42 ± 16 × 10− 9 mol/m2 or 1.7 × 10− 9 mol/L recalculated for the S/V-specific PMMA bottles used) and affinity (log KFe'W = 11.0 ± 0.3 m2/mol or 12.4 ± 0.3 L/mol, recalculated for the S/V-specific PMMA bottles used) are of similar magnitude as the iron capacity and -affinity of the natural ligands in the presently used seawater and thus cannot be ignored.Calculation of rate constants for association and dissociation of both Fe'L (iron bound to natural occurring organic ligands) and Fe'W (iron adsorbed on the wall of vessels) suggests that the two iron complexes are also of rather similar kinetics, with rate constants for dissociation in the order of 10 −4–10− 5 L/s and rate constants for association in the order of 108 L/(mol s). This makes that iron wall sorption should be seriously considered in small-volume experiments, both in assessments of shorter-term dynamics and in end-point observations in equilibrium conditions. Therefore, the present data strongly advocate making use of iron mass balances throughout in experiments in smaller volume set-ups on marine iron (bio) chemistry.  相似文献   

19.
The feeding behaviour of adults of the marine calanoid copepod Centropages hamatus was studied in laboratory experiments with ciliates and phytoplankton as food sources. The ingestion rate of algal (flagellates, diatoms) and ciliate prey (oligotrichs) as a function of prey concentration could be described by a Holling type III functional response, with close to zero ingestion rates at concentrations below 5 µg C l− 1. In general, ingestion of ciliates was higher than ingestion of algae, and maximum feeding rates by adult males reached were half the feeding rates of adult females at prey concentrations exceeding 50 µg C l− 1. When diatoms and ciliates were offered together C. hamatus (both sexes) fed exclusively on ciliates as long as they contributed with more than 5% to the mixture. This indicates the capability of active prey selection and switching between suspension feeding and ambush predation. Therefore, the feeding behaviour of adult C. hamatus can be characterised as omnivorous with a preference for larger motile prey. This implies a trophic level above two, if there is a sufficient abundance of protozoan food available.  相似文献   

20.
The seasonal and interannual variability of the air–sea CO2 flux (F) in the Atlantic sector of the Barents Sea have been investigated. Data for seawater fugacity of CO2 (fCO2sw) acquired during five cruises in the region were used to identify and validate an empirical procedure to compute fCO2sw from phosphate (PO4), seawater temperature (T), and salinity (S). This procedure was then applied to time series data of T, S, and PO4 collected in the Barents Sea Opening during the period 1990–1999, and the resulting fCO2sw estimates were combined with data for the atmospheric mole fraction of CO2, sea level pressure, and wind speed to evaluate F.The results show that the Atlantic sector of the Barents Sea is an annual sink of atmospheric CO2. The monthly mean uptake increases nearly monotonically from 0.101 mol C m− 2 in midwinter to 0.656 mol C m− 2 in midfall before it gradually decreases to the winter value. Interannual variability in the monthly mean flux was evaluated for the winter, summer, and fall seasons and was found to be ± 0.071 mol C m− 2 month− 1. The variability is controlled mainly through combined variation of fCO2sw and wind speed. The annual mean uptake of atmospheric CO2 in the region was estimated to 4.27 ± 0.68 mol C m− 2.  相似文献   

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