Μg Cl Research Articles

On the Quantitative Importance of Heterotrophic Microplankton in the Northern German Wadden Sea

To assess the importance of heterotrophic microplankton in the Wadden Sea, seasonal distribution and biomass of the main subgroups, that is, heterotrophic dinoflagellates, (separated into thecate and athecate forms), tintinnids, and aloricate ciliates, were studied in 1989 and 1990 in a total of six surveys covering the whole area of the northern German Wadden Sea. Heterotrophic microplankton biomass exhibited high spatial and temporal variation, ranging from 0 μg Cl−1 to 66 μg Cl−1, with maximum concentrations in spring., Mean stocks were lowest in winter (1.6 μg Cl−1) and highest in spring (11.7 μg Cl−1); intermediate concentrations were found in summer (8.5 μg Cl−1). In winter, the heterotrophic microplankton was dominated by tintinnids. In spring and summer, aloricate ciliates and dinoflagellates made up the largest part of the biomass. A pronounced feature was a shift within the dinoprotist group from athecate to thecate forms in summer. In spring, maxima of athecate dinoflagellate carbon were associated with blooms ofPhaeocystis globosa, indicating a close trophic relationship. From rough estimates of the daily grazing potential, based on microheterotrophic biomass and conversion factors from the literature, it may be concluded that heterotrophic microplankton temporarily share a main role in the transfer of food and energy to higher trophic levels within the pelagic system of the Wadden Sea.

Estimation of bacterial production through the coupling of (methyl 3H) Thymidine incorporation and several parameters over a Microcystis aeruginosa bloom in a hypereutrophic reservoir

AbstractThe coupling of the changes in bacterial quantitative and metabolic aspects during Microcystis aeruginosa bloom conditions together with several environmental parameters was studied in the hypereutrophic Villerest reservoir, France. Bacterial abundance varied from 5.20 to 21.28 × 106 bacteria‐mL−1, while bacterial biomass ranged between 75 and 507 μg C mL−1. These results confirmed the highly eutrophic status of the Villerest reservoir. The relative quantitative importance of attached bacteria increased as Microcystis proliferated. Methyl‐3H incorporation and D‐(U‐14C) glucose uptake varied from 8.99 to 60.57 × 106 cells‐mL−1, and 0.016 to 1.587 μg CL−1 h−1, respectively. Correlations between several abiotic and biotic parameters showed that phytoplankton regulated bacterial growth by releasing organic carbon which is directly uptaken by heterotrophic bacteria. In the hypolimnion, the sedimentation of decaying algae represented a substantial substrate for bacterial growth.

Organic halogen, heavy metals and biological activities in pristine and pulp mill recipient lake sediments

In order to create a basis for prognosing future intrinsic remediation potential of past pollution by pulping industry, we analyzed biochemical activities and levels of pollution in sediments dated with 210Pb and 137Cs. A small pristine forest lake and a pulp mill recipient area of a large oligotrophic Lake Saimaa were test sites. Sediment concentration of EOX ranged from 40 to 130 μg Cl (g d.w.)−1 in the pristine lake and from 770 to 4700 μg Cl (g d.w.)−1 in the pulp mill recipient area and the C:Cl (w/w) ratio of sediment organic matter ranged from 2000 to 5100 and 42 to 230, respectively. The organic matter in 10 to 20 years old pulp mill recipient sediment was mainly of waste water origin. The activity gradients of β-glucosidase, butyrate-esterase, methane oxidation potential and endogenous respiration from surface to deeper layers were less steep in polluted than in pristine sediment. Methane oxidation potential was 120 μmol CH4d−1 (g C)−1 at the sediment surface of pristine lake sediment and 26 μmol CH4d−1 (g C)−1 at the polluted site, endogenous respiration rates of the surface sediment were 670 and 310 μmol CO2 d−1 (g C)−1, respectively. In the most polluted layer we found a depressed potential for methane oxidation, inhibition of phosphatase and butyrate-lipase activities and moderately increased induction ratio of β-galactosidase to phosphatase in the SOS-Chromotest strain E. coli PQ 37. The results suggest that at the concentrations observed these effects in the sediment were not due to heavy metals.

Organic halogen, heavy metals and biological activities in pristine and pulp mill recipient lake sediments

In order to create a basis for prognosing future intrinsic remediation potential of past pollution by pulping industry, we analyzed biochemical activities and levels of pollution in sediments dated with 210Pb and 137Cs. A small pristine forest lake and a pulp mill recipient area of a large oligotrophic Lake Saimaa were test sites. Sediment concentration of EOX ranged from 40 to 130 μg Cl (g d.w.)−1 in the pristine lake and from 770 to 4700 μg Cl (g d.w.)−1 in the pulp mill recipient area and the C:Cl (w/w) ratio of sediment organic matter ranged from 2000 to 5100 and 42 to 230, respectively. The organic matter in 10 to 20 years old pulp mill recipient sediment was mainly of waste water origin. The activity gradients of β-glucosidase, butyrate-esterase, methane oxidation potential and endogenous respiration from surface to deeper layers were less steep in polluted than in pristine sediment. Methane oxidation potential was 120 μmol CH4 d−1 (g C)−1 at the sediment surface of pristine lake sediment and 26 μmol CH4 d−1 (g C)−1 at the polluted site, endogenous respiration rates of the surface sediment were 670 and 310 μmol CO2 d−1 (g C)−1, respectively. In the most polluted layer we found a depressed potential for methane oxidation, inhibition of phosphatase and butyratelipase activities and moderately increased induction ratio of β-galactosidase to phosphatase in the SOS-Chromotest strain E. coli PQ 37. The results suggest that at the concentrations observed these effects in the sediment were not due to heavy metals.

Distribution et caractérisation de la matière organique dissoute d'eaux naturelles de surface

Cette étude porte sur la caractérisation de la matière organique dissoute de différentes eaux de retenue et de rivière. Outre les outils analytiques généralement utilisés dans ce type d'approche, carbone organique dissous, carbone organique dissous biodégradable, absorbance dans l'ultraviolet, ultrafiltration et potentiels de réactivité avec le chlore et l'ozone, ce travail de recherche s'appuie sur la mise en œuvre d'une méthode de fractionnement du COD sur résines XAD-8 et XAD-4 utilisées en série permettant de distinguer trois fractions, les substances hydrophobes (substances humiques), les acides hydrophiles et les substances hydrophiles non adsorbées. Les eaux de retenue collectées affichent des teneurs en COD et des absorbances UV à 254 nm, synonyme de la présence de structures aromatiques, plus importantes que celles des eaux de rivière. Globalement, la matière organique de ces eaux est constituée de deux fractions, une hydrophobe (matière organique adsorbée sur résine XAD-8 à pH acide) et une hydrophile (matière organique non retenue sur résine XAD-8 à pH acide) quantitativement équivalentes. La fraction hydrophobe englobe toutefois l'essentiel des structures aromatiques. Néanmoins, il est intéressant de noter que la matière organique hydrophobe est proportionnellement plus abondante dans les eaux de retenue (51 à 62% du COD) que dans les eaux de rivière (41 à 50% du COD). En contre partie, les composés hydrophiles non adsorbés sur résines XAD représentent une fraction significativement plus importante dans les eaux de rivière que dans les eaux de retenue. Pour l'eau de la Loire, cas particulier pour lequel la distribution hydrophobes/hydrophiles correspond à 41%/59% en COD, l'étude de la distribution des masses moléculaires apparentes déterminée par filtration sur membrane 1000 daltons, a permis de souligner la prédominance des composés de plus faibles masses moléculaires (< 1000 daltons) comparativement aux autres eaux étudiées. Cet ensemble de résultats pourrait être associéà la présence plus importante de sédiments en suspension dans les eaux de rivière, les sédiments favorisant l'adsorption et/ou la complexation, en présence d'espèces métalliques, des matières humiques définies comme hydrophobes. En ce qui concerne la réactivité des eaux naturelles avec les oxydants, les demandes en chlore et en ozone, les PFTHMt et les PFTOX, sont proportionnels à la teneur en COD et à l'absorbance UV à 254 nm des eaux étudiées. Les potentiels de réactivité relatifs (rapportés à l'unité de carbone) sont d'autant plus élevés que l'absorbance relative des eaux (Abs UV/mg COD) est grande. Les eaux de retenue présentent, dans ce sens, des réactivités vis-à-vis des oxydants plus fortes que les eaux de rivière. Enfin, la teneur en CODB des eaux naturelles comprise entre 8 et 22% est difficilement reliable aux autres données obtenues.

Bacteria in sea ice and underlying brackish water at 54°26'5"N (Baltic Sea, Kiel Bight)

Bacterial response to the rare event of solid ice cover in the western Baltic Sea (Kiel Bight) was investigated from February to March 1996. Samples (ice cores, brine and water) were taken at a shallow, near-shore station at irregular time intervals. Bacterial abundance, biomass and production were measured in brine and the underlying water as were the concentrations of NO3, NO2, NH4, PO4 and SiO4. Vertical distributions of bacterial abundance, biomass, morphotypes and size classes and chlorophyll a and nutrients were investigated within sea ice. A bacterial growth experiment with brine bacteria was carried out to measure bacterial carbon production via total incorporation of [3H]thymidine (TTI) and [3H]leucine (TLI). During February the abundance, biomass and production of bacteria within brine exceeded values from under-ice water, whereas the opposite was observed in March. High NO3 and NH4 concentrations in ice and under-ice water of up to 112 µM and 55 µM, respectively, resulted in N:P ratios of 18 to 330. Algae and bacteria were considered to benefit from that nutrient supply. For bacteria this was supported by TTI and particularly high TLI rates during the ice situation, with TLI:TTI ratios of 25 to 213. The high TLI rates were due to a large degree of unspecific labeling by leucine and characterised the bacteria during winter 1996 as extremely active. Bacterial production (based on TTI) rose in water from 0.021 µg Cl-1 h-1 at the beginning to 0.909 µg Cl-1 h-1 at the end of the investigation, and in brine from 0.122 to 0.235 µg Cl-1 h-1. Abundance of bacteria in brine increased from 1.7 x 106 cells ml-1 initially to 2.8 x 106 cells ml-1 in March. The average cell volume of these bacteria was 0.2 µm3 whereas the bacteria in water reached only 0.08 µm3. The bacterial assemblage in the ice was dominated by large rods and in the water by small rods and cocci. Bacterivorous activity within sea ice was assumed to be reduced due to the specific vertical distribution of the different bacterial size classes. This was further supported by a good correlation between the development of the bacterial standing stock and the potential biomass, in sea ice as well as in the underlying water, calculated from generation times towards the end of the investigation. Low grazing pressure, high standing stocks of algae and sufficient substrate supply accounted for bacterial biomass within the ice and the underlying water that exceeded that from former winters by far. A comparison with Arctic and Antarctic sites demonstrated that the bacterial community within the sea ice showed many similarities to those found in sea ice of polar regions.

Autotrophic flagellates and diatoms in the Northeast Water polynya, Greenland: summer 1993

Abundance, biomass and distribution of autotrophic flagellates, autotrophic dinoflagellates and diatoms were measured in the Northeast Water (NEW) Polynya during summer, 1993, using epifluorescence microscopy (EFM) and high-pressure liquid chromotography (HPLC). Numerous discrepancies existed between results from EFM and HPLC. Phytoplankton communities determined microscopically at the depth of the chlorophyll maximum consisted primarily of flagellates in various size classes (average 1.3 × 107 cells 1−1, 8.5 μg Cl−1) and the small diatom Chaetoceros socialis (average 5×106 cells 1−1, 52 μg Cl−1), with subsurface maxima of both groups usually occurring close to the nitricline. A wide variety was observed in the composition of the phytoplankton community with respect to biomass of individual taxa. The biomass of autotrophic flagellates represented on average 23% of the total autotrophic biomass in all regions of the study area as defined by water mass type. Based on carbon units derived from pigment concentrations (HPLC), prasinophytes and haptophytes each contributed 24% to total flagellate (non-dinoflagellate) biomass and chrysophytes contributed 52%. In the northeast quadrant, influenced by the East Greenland Current, haptophyte contribution dropped to 9%. Most of the biomass of autotrophic flagellates was in cells < 8 μm in diameter; of diatoms, in cells < 10 μm in diameter. Highest picoplankton biomass (cells < 2 μm) occurred in ice-free water at moderate stability. The average contribution of autotrophic dinoflagellates to total autotrophic biomass was 6% (3 μg Cl−1, 1.7×105 cells 1−1). Ratios of microscopically measured autotrophic carbon to fluorometric chlorophyll a (i.e. community C:chl a) ranged from 11–265 (avg. 61), with maximum ratios attributable to regions dominated by C. socialis. Although differences between four areas of the NEW with respect to physical characteristics of the water column were observed, few corresponding biological differences could be verified. Similarly, phytoplankton community composition was weakly if at all correlated with physical or chemical characteristics of the water column. Future investigations should examine food web dynamics (i.e. grazing) and small-scale circulation to account for the mosaic pattern of phytoplankton features.

Low-dose infusion of recombinant tissue-type plasminogen activator in healthy volunteers to investigate the biodistribution of t-PA in the early phase of infusion

Summary Earlier observations suggested deviations from expected pharmacokinetics of recombinant tissue-type plasminogen activator (rt-PA) in the early phase of a low-dose infusion. A study with two low-dose intravenous infusions of rt-PA was performed on 10 healthy volunteers in an open randomized two-way crossover design. Doses of 150 and 300 μg rt-PA were administered over 40 min and blood samples were collected to measure tissue-type plasminogen activator (t-PA) antigen concentrations. Pre- and post-infusion data were used to predict a concentration profile during infusion without t-PA binding and these values were compared to actual measurements with the t-PA binding. The difference between the observed and predicted area under the concentration curve over the duration of infusion was 49 ng min/ml (95% confidence interval (C): +21, +78) for the 150 μg infusion and 29 ng min/ml (Cl: −4, +61) for the 300 μg infusion. The average amount of rt-PA that was apparently missing was 28 μg (Cl: +12, +44) after the 150 μg infusion and 21 μg (Cl: −9, +52) after the 300 μg infusion. These results indicate a distribution of t-PA over one or more compartments which might include or be the endothelium. Low-dose infusions could be valuable in defining this distribution in various patient groups and might be relevant in relation to the measurement of endothelial dysfunction.

Phytoplankton dynamics in the stratified water column of Lake Bonney, Antarctica

Phytoplankton populations in perennially ice-covered Lake Bonney, Antarctica grow in a unique non-turbulent environment. The absence of turbulence generated by winds or major streams, combined with strong vertical gradients in temperature and nutrients, create vertically stratified environmental conditions that support three discrete phytoplankton populations in the east lobe of this lake. Phytoplankton biomass and photosynthesis were measured in the east lobe of Lake Bonney during the winter-spring transicion (September) to mid-summer (January). During this period, irradiance beneath the ice increased from 0.03 to 1.9 mol quanta m−2 d−1. Chlorophylla concentrations ranged from 0.03 to 3.8 μl−1 within the trophogenic zone (just beneath the permanent ice cover to 20 m) and photosynthesis ranged from below detection to 3.2 μg Cl−1 d−1. Our results indicate: (1) phytoplankton photosynthesis began in late winter (before 9 September, our earliest sampling date); (2) maxima for phytoplankton biomass and production developed sequentially in time from the top to the bottom of the trophogenic zone, following the seasoral increase in irradiance; and (3) the highest photosynthetic efficiencies occurred in early spring, then decreased over the remainder of the phytoplankton growth season. The spring decrease in photosynthetic rates for shallower phytoplankton appeared to be related to nutrient availability, while photosynthesis in the deeper populations was solely lightdependent.

Bacteria associated with a marine planktonic copepod in culture. II. Degradation of fecal pellets produced on a diatom, a nanoflagellate or a dinoflagellate diet

Copepods (A cartia tonsa Dana) were allowed to feed on cultured algal species simulating the yearly boreal phytoplankton succession, where the spring is characterized by diatoms, the summer by nanoflagellates and the autumn by dinoflagellates. Degradation of freshly produced fecal pellets in suspension was followed over time by volume recording and estimation of carbon loss. The fecal pellets produced on a diatom diet were very dense and showed a significantly slower degradation than those produced on nanoflagellate or dinoflagellate diets. This indicates that the algal texture, i.e. the mechanical robustness given by inert structures, determines the degradation rate of the pellets. The degradation rate was also very dependent on the algal concentration for the grazer (565 μg Cl−1T1Ω = 75 h; excess food T1Ω = 12 h). Bacteria associated with the fecal pellets were monitored just after egestion and through 160–400 h of incubation. The bacteria associated directly with diatom-based pellets decreased rapidly in number over time and reached zero after 400 h. In contrast, the bacteria associated with the nanoflagellate- and dinoflagellate-based pellets increased in number, describing a saturation after 150 and 50 h, respectively. The bacterial number in the incubation water wherein the pellets were sus pended increased and reached a plateau after ˜100, 25 and 20 h for the diatom-, nanoflagellate- and dinoflagellate-based pellets, respectively. The carbon density of diatom-based pellets was lower than that of flagellate-based pellets. The difference in bacterial growth on carbon from the pellets indicates a difference in substrate quality, where diatom-based pellets are suggested to be a poor substrate compared to flagellate-based pellets. This leads to the conclusion, taking the dominating algal taxa and the pellet sedimentation rates into consideration, that flagellate-based fecal pellets are degraded in the surface waters in summer and autumn, while diatom-based pellets are likely to be degraded on the bottom of the sea in spring.

The use of transplanted cultured mussels ( Mytilus edulis) to monitor pollutants along the Ninety Mile Beach, Victoria, Australia—I. Extractable organohalogens (EOX)

Commercially cultured mussels ( Mytilus edulis) were transplanted from Port Philip Bay to multiple sites along the Ninety Mile Beach, Victoria, on six occasions to assess water column concentrations of extractable organohalogens (EOX). Mussels were deployed both before and after the commencement of the discharge of a secondary-treated mix of industrial, domestic and pulp and paper mill effluent in the vicinity of two of the deployment sites. Transplanted mussels maintained both body condition and flesh lipid concentrations during the periods of deployment. Mussel tissue EOX concentrations varied between deployment sites and over deployment times. Inter-site differences in EOX tissue concentrations were not consistent over time. Mussel tissue EOX concentrations were not correlated with physical characteristics of the shellfish. Background tissue EOX concentrations ranged from 16 to 69 μg Cl g −1 dry tissue wt. Mussels deployed in the vicinity of the effluent discharge plume contained marginally-elevated tissue concentrations of EOX. However, these concentrations were not significantly higher than concentrations present in tissue from mussels deployed at control sites.

Organic matter in the Elbe estuary

In the low salinity region of the Elbe estuary in March–April 1992 the turbidity zone was characterized by high loads of suspended matter, 7% of which was organic material (750 μM C) at the surface. Particulate nitrogen, phosphorus and carbohydrates concentrations reached 55 μM N, 10 μM P and more than 15 μM glc. eq., corresponding to 13% of total C, at the surface and increasing threefold near the bottom. In spite of the peaking of particulate organic material levels in the maximum turbidity zone, there were only consistent qualitative changes in total particulate C, N, P, and carbohydrates along the Elbe estuary. Downstream, both the percentage of particulate organic material and the turbidity: organic material ratio decreased, indicating decomposition in the upper estuary and dilution with inorganic suspended matter from the lower estuary. Diatoms, the dominant phytoplankton group, decreased from the upper reaches towards the turbidity zone by 0.3 (surface) and 1.5 mg C l−1 (bottom). This corresponded to 12 and 60% of the decrease in total particulate carbon. Estimated local input of organic carbon by primary production (21 μg Cl−1d−1) was almost compensated by calculated minimum grazing (14 μg C l−1d−1). Considering net primary production and grazing, the dissimilation by zooplankton (5 μg C l−1d−1) and heterotrophic bacterial decomposition (48 μg C l−1d−1), when summed over the estimated flushing time (12 days) represented a loss of suspended organic matter of 0.6 mg Cl−1. Since this was only 20% of the observed decrease in particulate carbon, significant dilution processes must be assumed. Dissolved organic nitrogen decreased from 35 to 10 μM N and dissolvd organic phosphorus from 0.6 to 0.1 μM P towards the sea, mainly due to dilution. The distribution of phosphate, with highest loads in the turbidity maximum of 2.4 μM, suggested an interaction with the accumulated load of particulate material.

Occurrence and toxicity of persistent pollutants in surface microlayers near an incineration plant

Surface microlayers exposed to smoke plumes from an incineration plant were collected and their toxicity and content of anthropogenic compounds determined. The enriched levels of Al, Mn, Cu and Zn indicated an anthropogenic exposure, which was confirmed by increased levels of AOX and the presence of PCBs in the microlayers. AOX was enriched about twice the level found in the subsurface water (55 μg Cl L −1), which pointed to an airborne, local source. The mortality of the brine shrimp Artemia spp. changed in a dose-response manner after exposure to the microlayer. The crustacean Nitocra spinipes was not affected by the microlayer and no response was shown when the Microtox® method was used.

Nitrogen metabolism by heterotrophic bacterial assemblages in Antarctic coastal waters

Field studies to examine the in situ assimilation and production of ammonium (NH4+) by bacterial assemblages were conducted in the northern Gerlache Strait region of the Antarctic Peninsula. Short term incubations of surface waters containing 15N-NH4+ as a tracer showed the bacterial population taking up 0.041–0.128 μg-atoms Nl−1d−1, which was 8–25% of total NH4+ uptake rates. The large bacterial uptake of NH4+ occurred even at low bacterial abundance during a rich phytoplankton bloom. Estimates of bacterial production using 3H-leucine and -adenine were l.0μgCl−1 d−1 before the bloom and 16.2 μg Cl−1 d−1 at the bloom peak. After converting bacterial carbon production to an estimate of nitrogen demand, NH4+ was found to supply 35–60% of bacterial nitrogen requirements. Bacterial nitrogen demand was also supported by dissolved organic nitrogen, generally in the form of amino acids. It was estimated, however, that 20–50% of the total amino acids taken up were mineralized to NH4+. Bacterial production of NH4+ was occurring simultaneously to its uptake and contributed 27–55% of total regenerated NH4+ in surface waters. Using a variety of 15N-labelled amino acids it was found that the bacteria metabolized each amino acid differently. With their large mineralization of amino acids and their relatively low sinking rates, bacteria appear to be responsible for a large portion of organic matter recycling in the upper surface waters of the coastal Antarctic ecosystem.

Assimilable organic carbon concentrations in Southern California surface and groundwater

Bacterial regrowth potential in Southern California surface and groundwaters was evaluated for assimilable organic carbon (AOC) concentrations using two bioassays. Untreated and ozonated groundwaters were tested to determine variation in AOC with well site, season and static water depth. The mean total AOC concentration (Pseudomonas P17 + Spirillum NOX) for untreated groundwater was 54 μg carbon (C) l−1. Ozone treatment resulted in a 2 to 10-fold increase in AOC with an average concentration of 254 μg cl−1. Highly colored groundwaters (containing up to 250 platinum color units, pcu) were ozonated with 7 mg l−1 which was sufficient to remove up to 75 pcu of color but often resulted in AOC concentrations exceeding 500 μg Cl−1. In comparison, AOC levels in untreated surface waters were generally greater than 100 μg Cl−1 and showed less of an increase after ozonation than did groundwaters. Total organic carbon (TOC) concentrations ranged from 0.2 to 5.7 mg l−1 and most groundwater samples contained less than 1 mg l−1 TOC. There was no correlation between AOC and chemical parameters such as DOC, color or u.v. absorbance (254 nm). Ratios of AOC to DOC ranged from 0.5 to 31% which suggests that the majority of the organic carbon in groundwater and surface waters is biologically stable. In summary, AOC levels appeared to vary with well location and possibly with season. Therefore, routine monitoring of source and treated water must be conducted on a site specific basis to determine bacterial regrowth potential or biofilm formation. Appropriate treatment strategies can then be developed, on an area by area basis, to remove or reduce AOC levels.

Discontinuous-flow potentiometric determination of chloride in a large-volume wall-jet cell using an ion-selective electrode based on a silver chloride film chemically deposited on a silver iodide support

A robust and sensitive chloride ion-selective electrode can be prepared by modifying the surface of an iodide-selective electrode using the chemical reaction with mercuric chloride in an oxidizing medium containing excess chloride. A thin film of silver chloride is thus formed ensuring a rapid and reproducible response to chloride. The analytical parameters of this electrode are similar to those of commercial silver chloride ion-selective electrodes, but its electrical impedance and signal noise are substantially lower and the response somewhat faster. Its sensitivity toward surfactants is somewhat suppressed. The electrode was used for discontinuous flow potentiometric (DFP) determinations in a large-volume wall-jet cell in which the electrode surface can be continuously reactivated by a cleaning solution contained in the cell. The method was applied to determination of chloride in ground waters from an industrial waste dumping site. The limit of determination is low 9 μg Cl −/l (2.6 × 10 −7 M), the precision good (the relative standard deviation varies from 0.6 to 3.0% for chloride contents from 2.90 to 0.15 mg/l, respectively) and the method correlates satisfactorily with the results of an indirect AAS determination of chloride. The sample throughput is high—90 measurements can be carried out per hour, corresponding to 30–40 determinations per hour.

Seasonal Evolution of Microplanktonic Communities in the Estuarine Front Ecosystem of the Rhône River Plume (North-western Mediterranean Sea)

Seasonal evolution of microplanktonic communities was examined throughout the water column of the Rhône River outflow plume. Because of the lack of tide, the water column in the plume area corresponds to a three-layered system: an upper freshwater layer (plume layer) overlying Mediterranean seawater (seawater layer) and an intermediate layer (frontal layer) corresponding to the discontinuity. The three layers displayed different compositions of planktonic community. Except for bacteria, which were more abundant in the plume water during spring and summer, microorganisms were most abundant in the frontal water. Seasonal analysis showed a succession of microbial populations: primary producers (phytoplankton, autoflagellates) peaked in spring while heterotrophic organisms (bacteria, heteroflagellates) were more abundant in summer. In winter, the primary producers were cyanobacteria. Bacterial density and production were dependent upon the combined influence of temperature variation and nutrient concentration. The highest values of bacterial production were observed in the frontal layer. They were about 25 μg Cl -1 day -1, that is, respectively, two and three times more than the bacterial production in the freshwater and the seawater layers. Mortality rates were highest in the plume water (0·51 to 0·57 day -1), and only 60-70% of the mortality was due to the grazing. In the plume layer, the growth rate was twice in the fall of that in spring (1·34 against 0·51 ). The average growth rate in the frontal layer (1·57 day -1) was highest of the three layers and was coupled with the lowest mortality rate (0·22 day -1). In the frontal layer, the flagellate carbon requirement was only one tenth of the bacterial carbon production.

Phytoplankton around Elephant Island, Antarctica

Phytoplankton studies were conducted in a 4·104 km2 grid around Elephant Island, Antarctica, during January–March 1991. In addition to profiling studies at 50 stations during each of two cruises, pumped surface water was used to continuously record in vivo chlorophyll-a (chl-a) fluorescence and beam attenuation coefficients (ct). Measurements on discrete samples included chl-a, phytoplankton organic carbon (Ac), and total particulate organic carbon (POC). Equations were developed which permitted contour-mapping of chl-a and POC throughout the entire grid based on continuous measurements of in vivo chl-a fluorescence and ct values. Phytoplankton abundance increased from January–February (cruise I) to February–March (cruise II) as evidenced by mean surface chl-a values (0.8 and 1.34 μg l−1, respectively) and mean Ac values for the upper 20 m of the water column (21.3 and 39.8 μg Cl−1, respectively). Microplankton accounted for 29% (cruise I) and 40% (cruise II) of the total phytoplankton, based on direct measurements of chl-a. Patterns for integrated values of chl-a, Ac and POC were similar to patterns of concentrations in surface waters. The richest areas of phytoplankton were north of Elephant and King George Islands, which coincided with high krill density areas.

Bacterial activity along a trophic gradient

Bacterial biomass, secondary production, and extracellular enzymatic activity [α-glucosidase and leucine-aminopeptidase, measured as cleavage of artificial fluorogenic substrates 4-methyl umbelliferyl (MVF) α-D-glucopyranoside and L-leucine 7-amido-4-methyl coumarin (MCA)] were measured along a trophic gradient in the Northern Adriatic Sea in four ecologically different situations. Bacterial parameters were compared with chlorophyll a and inorganic and organic nutrient concentrations. Bacterial secondary production and extracellular enzymatic activity markedly changed among different seasons and along the trophic gradient. Average bacterial secondary production increased from 0.61 to 2.09 µg Cl(-1) hour(-1) preceding a bloom, to 2.09 µg Cl(-1) hour(-1) during the bloom, decreasing again to 0.81 and 0.83 µg Cl(-1) hour(-1) in the post-bloom and summer periods, respectively (values from 0.5 m depth). Leucine-aminopeptidase activity showed more consistent trends than α-glucosidase activity. Average values of leucine-aminopeptidase activity, measured by enzymatic release of MCA, increased from a pre-bloom value of 164.0 to 1,712.0 (nM MCA) hour(-1) released during a bloom, decreasing to 298.5 and 133.7 (nM MCA) hour(-1) released for the post-bloom and summer situation, respectively (values from 0.5 m depth). Average growth rates decreased during the bloom, whereas average extracellular enzymatic activity levels expressed on a cell basis increased by an average factor of 2. Along the trophic gradient, a consistent increase in bacterial secondary production could be observed in all but the summer situation (values from 0.5 m depth). Leucine-aminopeptidase activity also showed positive trends along the gradient, while α-glucosidase activity did not exhibit such a clear trend. Bacterial biomass trends were less obvious considering both seasonal changes and the tropic gradient. Highly significant interrelations were detected between bacterial proteolytic activity, secondary production, chlorophyll a content, and nitrate concentrations, especially in the surface horizon.

Planktonic ciliates in Southampton Water: abundance, biomass, production, and role in pelagic carbon flow

The abundance and biomass of marine planktonic ciliates were determined at monthly intervals at two stations in Southampton Water between June 1986 and June 1987. The two stations, an outer one at Calshot and an inner one at N. W. Netley, were subject to differing marine and terrestrial influences. The potential ciliate production at cach station on each visit was estimated from these data. Enumeration of ciliates and measurements of biovolume were performed on Lugol's iodinepreserved samples and potential production was calculated using a predictive relationship based on temperature and cell volume. Heterotrophic ciliate abundance and biomass were greatest at both stations during spring and summer months, with respective maxima of 16x103 organisms 1-1 and 219 μg Cl-1 recorded at N. W. Netley. Estimates of the potential production of the ciliate community ranged from 100% of the energy requirements of metazoan zooplankton at these locations, although comprising only 8 and 10% of their available food.