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1

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Abundance and biomass of heterotrophic microorganisms in Lake Tanganyika (2005)

PIRLOT, SAMUEL ; VANDERHEYDEN, JULIE ; DESCY, JEAN-PIERRE ; [et al.]

Oxford, UK : Blackwell Science Ltd

Freshwater biology 50 (2005), S. 0

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ISSN: 1365-2427

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: 1. This study focused on heterotrophic microorganisms in the two main basins (north and south) of Lake Tanganyika during dry and wet seasons in 2002. Bacteria (81% cocci) were abundant (2.28–5.30 × 106 cells mL−1). During the dry season, in the south basin, bacterial biomass reached a maximum of 2.27 g C m−2 and phytoplankton biomass was 3.75 g C m−2 (integrated over a water column of 100 m).2. Protozoan abundance was constituted of 99% of heterotrophic nanoflagellates (HNF). Communities of flagellates and bacteria consisted of very small but numerous cells. Flagellates were often the main planktonic compartment, with a biomass of 3.42–4.43 g C m−2. Flagellate biomass was in the same range and often higher than the total autotrophic biomass (1.60–4.72 g C m−2).3. Total autotrophic carbon was partly sustained by the endosymbiotic zoochlorellae Strombidium. These ciliates were present only in the euphotic zone and usually contributed most of the biomass of ciliates.4. Total heterotrophic ciliate biomass ranged between 0.35 and 0.44 g C m−2. In 2002, heterotrophic microorganisms consisting of bacteria, flagellates and ciliates represented a large fraction of plankton. These results support the hypothesis that the microbial food web contributes to the high productivity of Lake Tanganyika.5. As the sole source of carbon in the pelagic zone of this large lake is phytoplankton production, planktonic heterotrophs ultimately depend on autochthonous organic carbon, most probably dissolved organic carbon (DOC) from algal excretion.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2427.2005.01395.x

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2

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Estimating phytoplankton carbon from microscopic counts: an application for riverine systems (2000)

Gosselain, Véronique ; Hamilton, Paul Brian ; Descy, Jean-Pierre

Springer

Hydrobiologia 438 (2000), S. 75-90

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ISSN: 1573-5117

Keywords: phytoplankton counts ; biomass ; centric diatoms ; river

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Algal biomass, in addition to cell numbers, is a measure of the successful conversion of inorganic to organic carbon. Consequently, carbon is the main currency used in aquatic models and in flux and budget studies. On the other hand, microscopic observation and counts remain the only means for determining species composition and biomass, which is relevant to many aspects of aquatic ecology. In this study, we focus on the way to convert biovolume to carbon biomass for algal assemblages of two rivers, using a computerized system that records dimensions of phytoplankton (Gosselain & Hamilton, 2000). We first compare different equations found in the literature for converting algal cell volume to cellular carbon content. We then evaluate the accuracy of a biomass estimate based on less time-consuming measurements, using pre-determined biovolume values instead of measuring cells in all samples. Biovolume/carbon equations are evaluated using total phytoplankton carbon biomass determined from measured chlorophyll a. Equations established for freshwater taxa seem to provide better estimates of algal biomass in the two case studies presented here, the Rideau and Meuse rivers (Canada and Belgium, respectively) than do more numerous equations defined for marine taxa. Furthermore, equations that make a distinction between diatoms and other algae appear more appropriate than those considering all algal groups as a whole. Finally, mean values of algal biovolumes, determined using sufficient measurements of cell dimensions from representative sampling series, may prove sufficient for carbon estimates of taxa in relatively homogenous size ranges. The careful choice of appropriate volumetric shapes and taxa categories remains of prime importance to get precise results.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1004161928957

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Development and ecological importance of phytoplankton in a large lowland river (River Meuse, Belgium) (1994)

Descy, Jean-Pierre ; Gosselain, Véronique

Springer

Hydrobiologia 289 (1994), S. 139-155

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ISSN: 1573-5117

Keywords: potamoplankton ; regulated river ; transport of carbon and nutrients ; photosynthesis ; respiration ; dynamics

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The ecological importance of the River Meuse phytoplankton with regard to carbon and nutrient transport has been examined in two reaches of the Belgian course of the river. Field measurements of total particulate organic carbon (POC), particulate organic nitrogen (PON) and particulate phosphorus (PP) show that the large autochtonous production of organic matter strongly affects the carbon and nutrient budget of the aquatic system. During the growing season, phytoplankton accounts for nearly 60% of the POC and dominates the PON. Calculations of the carbon and oxygen budget in the upper reach of the Belgian Meuse demonstrates that the ecosystem is autotrophic, i.e. that autochtonous FPOM (fine particulate organic matter) production is the major carbon input. This suggests that in large lowland rivers, primary production (P) may exceed community respiration (R), i.e. P:R〉1, whereas they are assumed to be heterotrophic (P:R〈1) in the River Continuum concept. The question of maintenance of phytoplankton in turbid mixed water columns is also addressed, and the case of the River Meuse is treated on the basis of studies of photosynthesis and respiration (ETS measurements). The results suggest that the potamoplankton may show some low-light acclimation, through an increase of chlorophyll a relative to biomass, when it comes to deep downstream reaches, and that algal respiration rate may be reduced. A simulation of the longitudinal development of the algal biomass shows the different phases of algal growth and decline along the river and brings support to the ‘importation hypothesis’ for explaining maintenance of potamoplankton in the downstream reaches.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00007415

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4

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The zooplankton of the lower river Meuse, Belgium: seasonal changes and impact of industrial and municipal discharges (1996)

Marneffe, Yves ; Descy, Jean-Pierre ; Thomé, Jean-Pierre

Springer

Hydrobiologia 319 (1996), S. 1-13

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ISSN: 1573-5117

Keywords: river ; zooplankton ; seasonal succession ; pollution ; Meuse

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Between 1991 and 1993, samples were collected upstream and downstream of the industrial basin and urban centre of Liège. Rotifers and crustaceans (cladocerans and copepods) were identified and counted. Their population dynamics were related to physical and chemical factors (temperature, oxygen, ammonium, nitrates, nitrites, phosphates) and to phytoplankton biomass. The zooplankton was dominated by rotifers; crustaceans (cladocerans and copepods) were less abundant. There was a succession of groups and species, some thriving in the spring and others in summer or autumn. The dominant rotifer species were Brachionus calyciflorus Pallas, Brachionus angularis Gosse, Keratella cochlearis (Gosse) and Synchaeta spp.; B. calyciflorus and B. angularis are spring species. K. cochlearis was present between May and November. Crustacean biomass was important in summer and autumn, but the faunal spectrum and biomass also varied with sampling location. Low spring and summer discharges allowed the phytoplankton to develop significantly. The zooplankton development followed a similar pattern. During low flow, when plankton populations become established, some declines in phytoplankton could only be explained by sedimentation and grazing pressure by zooplankton. Although these factors provided a good explanation of the longitudinal variation, some local conditions (e.g. oxygen deficit, high level of phosphate) also induced changes (e.g. industrial and municipal waste water discharge).

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00020966

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5

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Grazing by large river zooplankton: a key to summer potamoplankton decline? The case of the Meuse and Moselle rivers in 1994 and 1995 (1998)

Gosselain, Véronique ; Descy, Jean-Pierre ; Viroux, Laurent ; [et al.]

Springer

Hydrobiologia 369-370 (1998), S. 199-216

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ISSN: 1573-5117

Keywords: potamoplankton ; plankton interactions ; in situ grazing ; European rivers

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract To explain summer declines in phytoplankton biomass in large rivers, we compared the effect of zooplankton grazing on the planktonic algae of two large European rivers, the Meuse and the Moselle. In situ grazing was measured during two years (1994 and 1995), using the Haney method. Total zooplankton community filtration rates recorded in the river Meuse ranged between 1 and 32% of the water volume filtered per day. A drastic algal decline was observed early July both years and may be explained by high densities of a rotifer-dominated zooplankton community (500–700 ind. l-1) with more than 75% of Brachionus calyciflorus. During the summer period in 1994, when grazing was over 20%, edible algal biomass was controlled by a diversified rotifer community (up to 2500 ind. l-1), while a non-edible algal assemblage developed. In contrast, phytoplankton biomass remained comparatively low in the Moselle throughout the low-flow period, as did zooplankton numbers during most of this time (fewer than 200 ind. l-1 during the summer period). The proportion of crustaceans in this zooplankton was rather higher than in the Meuse, and they dominated at times, in biomass as well as in numbers. Nevertheless, measured in situ grazing rates (1–15%) could not explain the low summer algal biomass, even if low filtration rates may at times represent a significant carbon loss for phytoplankton, when and where net algal production was low. As a conclusion, the role of phytoplankton – zooplankton interactions in controlling algal biomass in large rivers is discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1017071909997

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6

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The phytoplankton community of the River Meuse, Belgium: seasonal dynamics (year 1992) and the possible incidence of zooplankton grazing (1994)

Gosselain, Véronique ; Descy, Jean-Pierre ; Everbecq, Etienne

Springer

Hydrobiologia 289 (1994), S. 179-191

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ISSN: 1573-5117

Keywords: potamoplankton ; community structure ; European rivers ; grazing

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Qualitative and quantitative aspects of the phytoplankton of the River Meuse were studied during 1992, at a point 537 km from the source. The phytoplankton was dominated by diatoms and green algae. The Stephanodiscus hantzschii-group was especially prominent. Other important taxa were Cyclotella meneghiniana, small Cyclotella and Thalassiosira, Aulacoseira ambigua and Nitzschia acicularis. Cell abundances varied from less than 1000 units ml−1 to about 25 000 – 30 000 units ml−1 during the blooms. The Stephanodiscus hantzchii-group constituted almost entirely the first spring bloom. During the summer period, small Thalassiosiraceae developed markedly and large Thalassiosira weissflogii appeared. During this period, green algae dominated diatoms as expressed in cell abundances. The main Chlorococcales were Scenedesmus quadricauda, Scenedesmus div. sp., Dictyosphaerium ehrenbergianum and Pediastrum duplex. Dinophyceae contributed a significant biomass during the summer period. Total biomass varied between 100 and 3 650 µg Cl−1. As previously observed (Descy, 1987), the factors regulating the phytoplankton growth were clearly physical variables: discharge, temperature and irradiance. However, in the summer period, low abundances might indicate a regulation by biotic factors. The impact of grazing by zooplankton is discussed, on the basis of observations of zooplankton development in the River Meuse and on the basis of simulation by a mathematical model. A comparison is carried out with recent data of phytoplankton in large European rivers.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00007419

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