Build-up and decline of summer phytoplankton biomass in the eastern Weddell Sea,Antarctica

The seasonal development and decline of phytoplankton was investigated in the eastern Weddell Sea during summer and fall 1991. During the first half of the study (15 Jan–13 Feb) in an area off Vestkapp, favourable irradiance/mixing regimes initiated net phytoplankton growth in ice-free waters on the shelf and in stretches of open water over the partially ice-covered deep ocean. Chi a concentrations in the upper water column were moderate (0.2–0.8 g l^–1), but significantly above winter values. Later in the season (16 Feb–11 March), a phytoplankton bloom with surface Chl a concentrations ranging from 1.6–2.3 g l^–1 was encountered in an area further to the east. We suggest that the upper water column must have been stratified in this region for time scales of weeks to faciliate bloom development. Bacterial biomass and productivity generally paralleled the seasonal development of the phytoplankton. Nitrate concentrations in the upper mixed layer were substantially lower than would be expected from the existing phytoplankton standing stock, suggesting that heterotrophic consumption of organic matter by bacteria and zooplankton removed a large fraction of the primary production. The shallow seasonal pycnocline was eventually eroded by the passage of a storm, resulting in a homogeneous distribution of phytoplankton biomass over the entire water column, followed by sedimentation and deposition of phytodetritus on the sea floor. After the storm induced destratification, bacterial productivity was particularly high, amounting to more than half of the primary production (range: 10%–120%) in the upper water column. Subsequently, phytoplankton biomass in the upper water column decreased to values <1 g Chl a l^–1. The combination of low incident irradiances and incessant deep mixing prevented the phytoplankton biomass to increase again. During the last week of the investigation, extensive new-ice formation was observed. A major fraction of the residual surface plankton was incorporated into new sea ice, thus terminating the pelagic growth season of the phytoplankton in the eastern Weddell Sea.     

Distribution and activity of bacteria in the headwaters of the Rhode River Estuary,Maryland, USA

A transect along the axis of the headwaters of a tidal estuary was sampled for microbial, nutrient, and physical parameters. Chlorophylla averaged 42g 1^–1 and phytoplankton comprised an estimated 80% of the total microbial biomass as determined by adenosine triphosphate (ATP). Bacterial concentrations ranged from 0.3–53.9×10⁶ cells ml^–1 and comprised about 4% of the total living microbial biomass. Bacterial production, determined by³H-methyl-thymidine incorporation was about 0.05–2.09× 10⁹ cells 1^–1 h^–1, with specific growth rates of 0.26–1.69 d^–1. Most bacterial production was retained on 0.2m pore size filters, but passed through 1.0m filters. Significant positive correlations were found between all biomass measures and most nutrient measures with the exception of dissolved inorganic nitrogen nutrients where correlations were negative. Seasonal variability was evident in all parameters and variability among the stations was evident in most. The results suggest that bacterial production requires a significant carbon input, likely derived from autotrophic production, and that microbial trophic interactions are important.     

The contribution of size-fractionated plankton to biomass and primary production of phytoplankton in saline–alkaline ponds

Primary productivity, biomass and chlorophyll-a of size fractionated phytoplankton (<0.22 m, <3 m, <8 m, <10 m, <40 m, <64 m, <112 m and <200 m) were estimated in 6 ponds and 5 experimental enclosures. The results showed that the planktonic algae less than 10 m are important in the biomass and production of phytoplankton in saline–alkaline ponds. The production of size fractionated phytoplankton corresponding to <112 m, <10 m and <3 m in saline–alkaline ponds were 10.5 ± 6.6 , 8.6 ± 5.4 and 0.33 ± 0.1 mgC l^–1 d^–1, respectively. Mean community respiration rate was 1.80 ± 0.73, 1.69 ± 0.90 and 1.38 ± 1.12 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) were 1.61, 8.30 and 0.33 mgC l^–1 d^–1, respectively. The ratio of those to the total phytoplankton production was 15%, 79% and 3%, respectively. The mean respiration rate of the different size groups was 0.11, 0.31 and 1.38 mgC l^–1 d^–1; the ratio of those to total respiration of phytoplankton was 6%, 17% and 77%, respectively. The production of size-fractionated phytoplankton corresponding to <200 m, <10 m and <3 m in enclosures was 2.19 ± 1.63, 2.08 ± 1.75 and 0.22 ± 0.08 mgC l^–1 d^-1, respectively. Mean community respiration rates were 1.25 ± 1.55, 1.17 ± 1.42 and 0.47 ± 0.32 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton was 0.11, 1.86 and 0.22 mgC l^–1 d^–1, respectively. The ratio of those to the total production of phytoplankton was 5%, 85% and 10%, respectively. The mean respiration rate of different size groups were 0.08, 0.72 and 0.46 mgC l^–1 d^–1, the ratio of those to total respiration of phytoplankton was 6%, 57% and 37%, respectively. The concentrations of chlorophyll-a of the phytoplankton in the corresponding size of micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) plankton in the experimental ponds were 19.3, 98.2 and 11. 9 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 15%, 76% and 9%, respectively. The concentrations of chlorophyll-a of phytoplankton micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton in enclosures were 1.7, 34.3 and 3.0 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 4%, 88% and 8%, respectively.     

Heterotrophic bacterial production in Lake Xolotlán (Managua) during 1988–1989

The biomass and production (thymidine incorporation) of heterotrophic bacterioplankton has been assessed from July, 1988, to October, 1989. in Lake Xolotlán, Nicaraqua. Bacterial abundance was high, 2–3.10¹⁰ cells.l^–1, and bacterial biomass averaged ca. 0.75 mg C.l^–1, or roughly 20% of the partivculate organic carbon. Bactrial production averaged between 3.5–5 g C.l^–1.h^–1 and on a areal basis was 650–959 mg C.m^–2.d^–1 or 13–20% ofthe primary production. Although bacterial production (volumetric basis) was typical for eutrophic lakeks, the bacterial specific growth rate was low, the bacteial population doubling time was ca. 1 week, perhaps indicating that there was a low grazing pressure on the bacteria.     

Bacterial lipolytic activity in a hypertrophic dead arm of the river Danube in Vienna

The kinetic parameters of lipase, bacterial secondaryproduction (BSP) and bacterial numbers (BN) were determined fortnightlyduringthe development of the summer phytoplankton bloom at twostationsof Alte Donau, a hypertrophic stagnant dead arm of the riverDanubein Vienna. Until the middle of August we observed a gradualincrease in lipase activity as well as BN and BSP rates tothe maximum of 19.9 nmol l^–1 h^–1,4.5×10⁹cells l^–1 and 8.1 g C l^–1 h^–1,respectively. Atthe end of August and during September we found a markeddecreasein all bacterial parameters, coinciding with a progressingincreaseof chlorophyll a concentrations at both sampling sites. Themaximalvalues of lipase V^max were determined in the bottom waterlayer (avg. 13.7±6.5 nmol l^–1 h^–1) probablyowingto the predominating importance of polymeric matter in thesubstrate pool for microheterotrophs in this water zone.Differential filtration experiments showed that 20.1% to56.3% ofthe total lipase activity and 4.2% to 9.0% of the totalbacterialnumbers in Alte Donau water samples occurred in 0.2-mfiltrate. Further experiments indicated that the highcontributionto lipase activity in the 0.2-m filtrate was rather dueto thepresence of 0.2 m filterable bacteria than to solubleenzymemolecules. Moreover, we observed higher bacterial lipaseactivityin 0.2 m filtrate than in unfiltered samples. Thepossibleinfluence of limiting factors on the metabolism of insitubacteria is discussed.     

Influence of hydrological seasonality on bacterioplankton in two neotropical floodplain lakes

Seasonal fluctuation in river stage strongly affects the ecological functioning of tropical floodplain lakes. This study was conducted to assess the influence of hydrological seasonality on bacterial production and abundance in two floodplain lakes of the Autana River, a blackwater river in the Middle Orinoco basin, Venezuela. Water samples for nutrient chemistry, chlorophyll a, and microbiological determinations were collected in two floodplain lakes and in the mainstem of the river during 1997–98. DOC and chlorophyll a concentrations were similar between mainstem and lake sites during high water when river and lakes were well connected but became different during the period of low water when the interaction was minimal. Higher values of bacterial production were observed in the floodplain lakes (0.62–1.03 g C l^–1 h^–1) compared to the mainstem sites (0.17–0.19 g C l^–1 h^–1) during the period of low water, while during the period of high water river and lake sites showed similar levels (0.04 g C l^–1 h^–1). Bacterial numbers followed bacterial production in the floodplain lakes, reaching higher numbers during the period of low water (1.41–2.40 × 10⁶ cells ml^–1). Availability of substrate and inorganic nutrients, pH, and inputs and losses of bacterial cells could be determining the observed seasonal patterns in bacterial production and abundance. The Autana lakes exhibited a strong seasonal pattern in the chemical and biological conditions, showing higher productivity during the lentic phase that lasted between 5 and 6 months.     

Seasonal changes in the dissolved free amino acid and DOC concentrations in a hypertrophic African reservoir and its inflowing rivers

Dissolved free amino acid (DFAA) concentration and composition and dissolved organic carbon (DOC) concentration were measured over 16 months at three depths in hypertrophic Hartbeespoort Dam, South Africa and in its two perenially inflowing rivers. The range of DFAA concentrations in the reservoir and both rivers were similar with dominant DFAA consisting of serine, glycine, alanine and ornithine in all three systems. The range of DOC concentrations in the rivers was 1.5–11.1 mg l^–1, the major river (Crocodile) having about twice the DOC concentration of the Magalies River. The DFAA/DOC ratios ranged between 0.02–1.1% in the Crocodile River and 0.13–3.7% in the Magalies River. DFAA and DOC concentrations were positively correlated to the Magalies River flow, but for the Crocodile River, which received domestic and industrial effluents, DOC was inversely correlated to flow. The source of DFAA in both rivers was mainly terrestrial, in contrast to the main DOC source in the Crocodile River which was the effluents. The DFAA load of the Crocodile River ranged between 0.22 and 208 kg C d^–1.DOC (5.0–24.8mg l^–1) in Hartbeespoort Dam generally decreased with depth but DFAA (15–4800 nmol l^–1) concentration showed no clear trend. The DFAA/DOC ratios varied between 0.02 and 2.9%. DFAA concentrations were correlated (r = 0.3, n = 30, p = 0.04) with bacterial numbers at 0 and 10 m only while no significant correlations were found with bacterial production, chlorophyll a concentration and phytoplankton primary and EDOC (extracellular DOC) production at any depth. The rate of bacterial utilization of DFAA was low compared with data from other lakes. Diurnal phytoplankton production of DFAA in the euphotic zone of the whole lake was calculated to vary between 268 and 30 780 t C d^–1 indicating autochthonous DFAA sources were dominant to allochthonous DFAA sources. The autochthonous production of DFAA was > 2 × gross bacterial production of the euphotic zone indicating that although DFAA concentrations were frequently < 10 g C l^–1, the rate of DFAA production exceeded bacterial requirements.     

Phosphate uptake capacity of summer phytoplankton of the Loosdrecht Lakes in relation to phosphorus loading and irradiance

Summer populations of the phytoplankton of the Loosdrecht Lakes were enclosed in laboratory scale enclosures (LSE), supplied with 7.5 g P.l^–1.d^–1 and 105 g P.l^–1.d^–1, respectively. The maximum initial phosphate uptake rate (V_m) was related to irradiance and primary production. At phosphate uptake saturating light-irradiance V_m values up to 4 times the V_m values in the dark were measured.The phosphate uptake capacity per unit dry weight remained more or less constant throughout the experiments in the LSE receiving the lower amount of phosphorus, and declined in the LSE receiving the higher amount of phosphorus. Within the range of V_m values measured (<10 g P.mg DW^–1.h^–1 or 1,3 g P. g chla ^–1.h^–1), the growth rate of the phytoplankton was not influenced by alterations in phosphorus availability.     

Phytoplankton biomass and primary production in semi-enclosed reef lagoons of the central Great Barrier Reef,Australia

Phytoplankton biomass and primary production rates within semi-enclosed reef lagoons of the central Great Barrier Reef were compared with adjacent shelf waters. Chlorophyll concentrations and surface primary production rates were usually higher in lagoons although seasonal differences were only significant during the summer. Nitrate concentrations were higher in lagoons than in shelf waters year-round. Nano- (<20 m size fraction) or pico-phytoplankton (<2 m size fraction) dominated phytoplankton biomass and production within reef lagoons throughout the year. Net phytoplankton (>10–20 m size fraction), however, were relatively more important in both reef lagoons and open shelf waters during the summer. Biomass-specific production within lagoons (range 41–90 mg C mg chl^–1 day^–1) was high, regardless of season. Lagoonal phytoplankton production (range 0.2–1.6 g C m^–2 day^–1) was directly correlated with standing crop and inversely related to lagoon flushing rates. Phytoplankton blooms develop within GBR reef lagoons during intermittent calm periods when water residence times exceed phytoplankton generation times.     

Bacterial production in a mesohumic lake estimated from [14C]leucine incorporation rate

Incorporation of [¹⁴C]leucine into proteins of bacteria was studied in a temperate mesohumic lake. The maximum incorporation of [¹⁴C] leucine was reached at a concentration of 30 nm determined in dilution cultures. Growth experiments were used to estimate factors for converting leucine incorporation to bacterial cell numbers or biomass. The initially high conversion factors calculated by the derivative method decreased to lower values after the bacteria started to grow. Average conversion factors were 7.09 × 10¹⁶ cells mol^–1 and 7.71 × 10¹⁵ m³ mol^–1, if the high initial values were excluded. Using the cumulative method, the average conversion factor was 5.38 × 10¹⁵ m^–3 mol^–1 I . The empirically measured factor converting bacterial biomass to carbon was 0.36 pg C m^–3 or 33.1 fg C cell^–1. Bacterial production was highest during the growing season, ranging between 1.8 and 13.2 g C liter^–1 day^–1, and lowest in winter, at 0.2–2.9 g C liter^–1 day^–1. Bacterial production showed clear response to changes in the phytoplankton production, which indicates that photosynthetically produced dissolved compounds were used by bacteria. In the epilimnion bacterial production was, on average, 19–33% of primary production. Assuming 50% growth efficiency for bacteria, the allochthonous organic carbon could have also been an additional energy and carbon source for bacteria, especially in autumn and winter. In winter, a strong relationship was found between temperature and bacterial production. The measuring of [¹⁴C]leucine incorporation proved to be a simple and useful method for estimating bacterial production in humic water. However, an appropriate amount of [¹⁴C]leucine has to be used to ensure the maximum uptake of label and to minimize isotope dilution.     

Phytoplankton dynamics in a deep, tropical, hyposaline lake

The annual variation of the phytoplankton assemblage of deep (64.6 m), hyposaline (8.5 g l^–1) Lake Alchichica, central Mexico (19 ° N, 97° W), was analyzed in relation to thermal regime, and nutrients concentrations. Lake Alchichica is warm monomictic with a 3-month circulation period during the dry, cold season. During the stratified period in the warm, wet season, the hypolimnion became anoxic. N–NH₃ ranged between non detectable (n.d.) and 0.98 mg l^–1, N–NO₂ between n.d. and 0.007 mg l^–1, N–NO₃ from 0.1 to 1.0 mg l^–1 and P–PO₄ from n.d. to 0.54 mg l^–1. Highest nutrient concentrations were found in the circulation period. Chlorophyll a varied from <1 to 19.8 g l^–1 but most values were <5 g l^–1. The euphotic zone (>1% PAR) usually comprised the top 15–20 m. Nineteen algae species were identified, most of them are typical inhabitants of salt lakes. Diatoms showed the highest species number (10) but the small chlorophyte Monoraphidium minutum, the single-cell cyanobacteria, Synechocystis aquatilis, and the colonial chlorophyte, Oocystis parva, were the numerical dominant species over the annual cycle. Chlorophytes, small cyanobacteria and diatoms dominated in the circulation period producing a bloom comparable to the spring bloom in temperate lakes. At the end of the circulation and at the beginning of stratification periods, the presence of a bloom of the nitrogen-fixing cyanobacteria, N. spumigena, indicated nitrogen-deficit conditions. The well-stratified season was characterized by low epilimnetic nutrients levels and the dominance of small single-cell cyanobacteria and colonial chlorophytes. Phytoplankton dynamics in tropical Lake Alchichica is similar to the pattern observed in some deep, hyposaline, North American temperate lakes.     

Dynamics of bacterioplankton in a mesotrophic French reservoir (Pareloup)

Bacterioplankton abundance, biomass and production were studied at a central station (35 m depth) from April 1987 to September 1988 in a mesotrophic reservoir. Bacterial production was calculated by the (³H) thymidine method.For the water column, integrated estimates of bacterioplankton abundance ranged from 2.3 10⁹ to 4.6 10⁹ cells l^–1, and carbon biomass from 0.037 to 0.068 mg C l^–1; the thymidine incorporation rates ranged from 0.8 to 17.2 picomoles l^–1 h^–1, leading to net bacterial production estimates of less than 0.7 µg C l^–1 d^–1 in winter to 18 µg C l^–1 d^–1 in summer. About 55% of the production occurred in the euphotic layers.Over the year, the bacterial carbon requirement represented 90% of the autotrophic production for the whole lake. It was five times lower than autotrophic production in spring, but twice as high in summer. This important temporal lack of balance suggests that not all the spring primary production products are consumed immediately and/or that other carbon sources probably support bacterial growth in summer.     

Bacterial and phytoplankton dynamics in a sub-tropical estuary

Heterotrophic bacterial and phytoplankton biomass, production, specific growth rates and growth efficiencies were studied in July 2001 and January 2002 during both spring and neap tides, along a tidal cycle, at three sites in a subtropical estuary. Major freshwater inputs located in the Northern region led to differences in both phytoplankton and bacterioplankton biomass and activity along the estuary. While in the Northern region phytoplankton is light-limited, with mean phytoplankton production (PP) between 1.1 and 1.9 μg C l⁻¹ h⁻¹ and mean specific growth rates (PSG) between 0.14 and 0.16 d⁻¹, the Southern region registered values as high as 24.7 μg C l⁻¹ h⁻¹ for PP and 2.45 d⁻¹ (mean PP between 3.4 and 7.3 μg C l⁻¹ h⁻¹; mean PSG between 0.28 and 0.57 d⁻¹). On the other hand, maximum bacterial production (BP: 63.8 μg C l⁻¹ h⁻¹) and specific growth rate (BSG: 32.26 d⁻¹) were observed in the Northern region (mean BP between 3.4 and 12.8 μg C l⁻¹ h⁻¹; mean BSG between 1.98 and 6.67 day⁻¹). These bacterial activity rates are among the highest recorded rates in estuarine and coastal waters, indicating that this system can be highly heterotrophic, due to high loads of allochthonous carbon (mainly derived from mangrove forest). Our results also showed that, despite that BP rates usually exceeded PP, in the Southern region BP may be partially supported (∼45%) by PP, since a significant regression was observed between BP and PP (r = 0.455, P < 0.001). Handling editor: P. Viaroli     

Vertical structure and photosynthetic activity of Lake Shira phytoplankton

This study was conducted to analyse vertical dynamics of phytoplankton distribution in Shira Lake during the summer stratification regime. From late June to September phytoplankton in Shira Lake were stratified with the maximum in the lower part of the thermocline, at a depth of 8–12 m, with a chlorophyll concentration up to 23 g and biomass up to 5 mg l^–1. Maxima of chlorophyll and biomass of cyanobacteria and green algae were in different layers. From June to September a major part of chlorophyll a was in green algae, while under ice – in cyanobacteria. The variable fluorescence proves high photosynthetic activity of algae in the depth assemblage. Epifluorescent analysis disclosed that additional light-harvesting pigments were better developed in cells from the depth maximum. The maximum of gross primary production calculated from fluorescence corresponded to the depth maximum of phytoplankton. Primary production over a season was 2.7 gO₂ m^–2. Formation mechanisms of the depth maximum of phytoplankton are discussed in this paper.     

Examining the relationship between bacteria and heterotrophic nanoflagellates in Funka Bay (Japan) using the size-fractionation method

The chemical and biological conditions, and the bacteria-heterotrophic nanoflagellate (HNF) relationship were investigated in the vicinity of Funka Bay, southwest of Hokkaido, Japan during early spring 1999. At the time of sampling, chlorophyll a concentration, bacteria, phycoerythrin rich-cyanobacteria, and HNF abundance were in the following ranges: 0.3–3.6 g l^–1, 2.5–5.6 × 10⁵ cells ml^–1, 0.6–1.2 × 10³ cells ml^–1, and 2.2–4.2 × 10³ cells ml^–1, respectively. Dissolved inorganic nitrogen, phosphate and silicate concentrations were in the ranges: 8.7–12.2 M, 0.9–2.0 M, and 21.6–25.5 M, respectively. Primary production ranged from 6.4 to 76.3 mg C m^–3 d^–1. Using water samples from regions of different productivity levels (in and outside bay), the bacteria - HNF relationship was uncoupled experimentally by the size-fractionation technique. Higher primary production (19.9 mg C m^–3 d^–1) in the bay supported higher bacterial growth rate (0.029 h^–1). However, outside the bay both primary production (6.4 mg C m^–3 d^–1) and bacterial growth rate (0.007 h^–1) were lower. The HNF growth rates and grazing rates were similar for both but by comparing both HNF grazing capacity and bacterial production, there was net decrease in bacterial abundance outside the bay and net increase inside the bay. The microbial parameters (rates and abundance) and the amount of carbon flow estimated through the phytoplankton – dissolved organic matter (DOM) – bacteria loop were different between the coastal station and the open ocean station. However HNF grazing and growth rates was similar for both stations.     

Variations saisonnières de la production primaire dans les eaux de surface de la rivière du Saguenay

Experiments of primary production were carried out at weekly intervals in the surface waters at one station (maximum depth of 20 m) in the Saguenay River, near Chicoutimi, during May–December 1978. The photic zone was very thin (maximum depth of 2 m). Phosphates are very low during the season sampling (maximum of 0.1 µat-g.^–1). Maximum of production rates and biomass are respectively 3.5 mg C.m^–3.h^–1 and 3.7 mg.m^–3. The river receives both industrial and urban runoff. Trace metals (Mercury, Copper, Lead, and Iron) seemed to be one of the important limiting factors for phytoplankton growth.

     

Enzyme formation by a yeast cell wall lytic Arthrobacter species: formation of amylase

The kinetics of amylolytic enzyme formation by a yeast cell wall lytic Arthrobacter species were studied. Cultivation on autoclaved cells of baker's yeast showed that amylase formation was closely related to trehalose and glycogen dissimilation. Growth on yeast glycogen (0.5%) proceeded quite rapidly ( = 0.31 h^–1) with extensive amylase formation during exponential cell multiplication and a further low increase in activity during the stationary phase. Beside amylolytic activity [450 units (U) l^–1] the formation of a relatively high level of -glucosidase (90 U l^–1) was detected, the latter almost exclusively bound to bacterial cells. Growth on 0.5% trehalose occurred at a reduced rate ( = 0.22 h^–1) with post-logarithmic enzyme synthesis in the stationary phase. Amylase activity attained a level of 1200 U l^–1, whereas -glucosidase was very low at 7.7 U l^–1. Continuous culture experiments in the chemostat showed maximal volumetric productivity of amylase (105 U l^–1 h^–1) at a dilution rate of 0.15 h^–1. Growth on various carbohydrates revealed low levels of amylolytic activity (<100 U l^–1), which were increased by a -1,4-glucans and oligosaccharides such as starch, dextrin, maltotriose and maltose. On 0.5% maltose, growth-associated enzyme synthesis (230 U l^–1) was detected at a reduced growth rate ( = 0.14 h^–1). Amylolytic enzyme preparations from the culture fluid showed an unusual cleavage pattern; acting on starch, the polymer was almost completely hydrolysed to maltotriose and maltose in a molar ratio of 3:1.Correspondence to: W. A. Hampel     

Contribution of flow cytometry to estimate picoplankton biomass in estuarine systems

Picoplankton (plankton 3 m) biomass was determined by flow cytometry in three European estuarine systems (Krka Estuary in Croatia, Rhône Delta in France, and Lena Delta and Laptev Sea in Russia). The size of natural phytoplankton groups was obtained by a calibration curve, with different picoplankton's strains (from 1.6 to 3.4 m), measured by a Coulter counter (size) and a flow cytometer (light-scattering). Two natural groups of picoplankton were identified by flow cytometry in the three systems: Synechococcus sp and picoeukaryotes. Picoplankton cells abundance ranged between: 2800 and 42000, 5000 and 37000, 1000 and 50000 cells ml^–1 in the Krka estuary, in the Rhône delta and in the Lena-Laptev system, respectively. In the Krka estuary, picoplankton biomass ranges between 11 and 68 gC l^–1. It can make up as much as 88% of the total photosynthetic plankton population and 50% of total organic particulate carbon. Picoplankton biomass was greater in the summer than in the autumn. At the halocline layer this biomass can attempt ca. 390 gC l^–1during the summer cruise. In the Rhône delta, a lower picoplankton biomass (6–39 gC l^–1) was observed at the end of the winter. These biomass represented between 0.4 and 22% of the particulate organic carbon, which could reach 71% of the total photosynthetic plankton biomass at the marine station. In the Lena-Laptev system, picoplankton biomass varied between 6 and 56 gC l^–1 in surface waters. Picoplankton biomass decreased with depth, but picoeukaryotes were still observed in deep samples (20, 30 m) in the Laptev Sea, showing a considerable autotrophic activity in spite of low temperatures (0–1 °C). Although the widely dispersed estuary geographic distribution and their different estuarine characteristics, the data point out that these small organisms can also play an important role in the transfer of organic carbon from rivers to oceans and that flow cytometry can be able to detect these small cells in turbid systems.     

Development of a continuous system for the degradation of a cyanuric acid by adsorbed Pseudomonas sp. NRRL B-12228

Cyanuric acid in high concentrations (15.5 mm) was degraded completely by Pseudomonas sp. NRRL B-12228 independently of glucose concentration. In the batch fermentations there was a relation between the glucose concentration, on the one hand, and the liberation of ammonia or production of protein, on the other. The greater the supply of carbon, the more biomass was produced, and fewer NH _inf4 ^sup+ ions were released. Continuous fermentations using adsorbed cells could be performed to degrade cyanuric acid. In spite of different glucose feeding there was only a negligible difference in residues of s-triazine. In a one-step continuous system with dilution rates between 0.021 h^–1 and 0.035 h^–1, even a ratio of 0.65 between glucose and cyanuric acid was not sufficient to degrade the cyanuric acid supplied (320–540 mol l^–1 h^–1) completely. When a continuous two-step system was applied with dilution rates between 0.035 h^–1 and 0.056 h^–1, the consumption of carbon source could be minimized while s-triazine degradation up to 860 mol l^–1 h^–1 was complete. In this way the ratio between glucose and cyanuric acid could be increased to 0.25 (molar C:N ratio = 0.33:1). Thereby the process was made considerably more economic.     

Heterotrophic bacterial activity and primary production in a hypertrophic African lake

The relationship between heterotrophic bacteria and phytoplankton in the epilimnion (0–10 m) of hypertrophic Hartbeespoort Dam, South Africa, was examined by statistically analyzing three years of parallel measurements of heterotrophic bacterial activity (glucose uptake) and phytoplankton particulate and dissolved organic carbon production. Algal biomass ranged between 4.0 and 921.1 mg Chl a m^-3 at the surface. Primary production varied between 69.5 and 3010.0 mg C m^-2h^-1 while algal production of dissolved organic carbon (EDOC) ranged from 2.5 to 219.2 mg C m^-2h^-1. Bacterial numbers reached a summer peak of 44.23 × 10⁶ cells ml^-1 in the first year and showed no depth variation. The maximum rate of glucose uptake, V_max, reached a peak of 5.52 g C l^-1h^-1. V_max, maximum glucose concentration (K_t + S_n) and glucose turnover time (T_t) were usually highest at the surface and decreased with depth concomitant with algal production. At the surface, V_max was correlated to EDOC (r = 0.59, n = 67, p < 0.001) and primary production (r = 0.71, n = 70, p < 0.001). At 5 and 10 m, V_max was correlated to integral euphotic zone (~ 4 m) algal production and bacterial numbers. Glucose turnover time was inversely related to integral algal production (r = -0.72, n = 70, p < 0.001) and less strongly to bacterial numbers. The data indicated that although bacterial numbers and biomass were low relative to algal biomass in this hypertrophic lake, the heterotrophic bacteria attained high rates of metabolic activity as a result of enhanced algal production of available organic carbon.