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  • 1
    Electronic Resource
    Electronic Resource
    Modelling the impact of benthic filter-feeders on the composition and biomass of river plankton (2003)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 48 (2003), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY 1. The POTAMON model [Everbecq E. et al. (2001) Water Research, 35, 901] has been used to simulate the effect of benthic bivalves (mainly Dreissena polymorpha) on the phytoplankton and zooplankton in a lowland Western European river (the Moselle). Here we use a modified version of the POTAMON model with five categories of phytoplankton (Stephanodiscus, Cyclotella-like, large diatoms, Skeletonema and non-siliceous algae) to model filter-feeding effects of benthic bivalves in the Moselle. Zooplankton has been represented in the model by two categories, Brachionus-like and Keratella-like rotifers.2. According to density estimates from field surveys (Bachmann V. et al. (1995) Hydroécologie Appliquée, 7, 185, Bachmann V. & Usseglio-Polatera P. (1999) Hydrobiologia, 410, 39), zebra mussel density varied among river stretches, and increased through the year to a maximum in summer. Dreissena filtration rates from the literature were used, and mussels have been assumed to feed on different phytoplankton categories (but less on large and filamentous diatoms) as well as on rotifers.3. The simulations suggest a significant impact of benthic filter-feeders on potamoplankton and water quality in those stretches where the mussels are abundant, their impact being maximal in summer. Consequently, different plankton groups were not affected to the same extent, depending on their period of development and on indirect effects, such as predation by mussels on herbivorous zooplankton.4. A daily carbon balance for a typical summer shows the effect of benthic filter-feeders on planktonic and benthic processes: the flux of organic matter to the bottom is greatly enhanced at high mussel density; conversely, production and breakdown of organic carbon in the water column are reduced. Mussel removal would drive the carbon balance of the river toward autotrophy only in the downstream stretches.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2003.01017.x
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  • 2
    Electronic Resource
    Electronic Resource
    Phytoplankton pigments and community composition in Lake Tanganyika (2005)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 50 (2005), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. A 2-year (2002–2003) survey of chlorophyll and carotenoid pigments is reported for two off-shore stations of Lake Tanganyika, Kigoma (Tanzania) and Mpulungu (Zambia), and from three cruises between those sites. Chlorophyll a concentrations were low (0.3–3.4 mg m−3) and average chlorophyll a integrated through the 100 m water column were similar for both stations and years (36.4–41.3 mg m−2). Most pigments were located in the 0–60 m layer and decreased sharply downward. Chlorophyll a degradation products (phaeophytins and phaeophorbides) were detected at 100 m depth, whereas carotenoids became undetectable. Temporal and seasonal variation of the vertical distribution of pigments was high.2. The biomass of phytoplankton groups was calculated from marker pigment concentrations over the 0–100 m water column using the CHEMTAX software. On average for the study period, chlorophytes dominated in the northern station, followed by cyanobacteria T1 (type 1, or Synechococcus pigment type), whereas cyanobacteria T1 dominated in the south. Cyanobacteria T2 (type 2, containing echinenone), presumably corresponding to filamentous taxa, were detected in the rainy season. Diatoms (and chrysophytes) developed better in the dry season conditions, with a deep mixed layer and increased nutrient availability. Very large variation in the vertical distribution of algal groups was observed.3. Our observations on phytoplankton composition are broadly consistent with those from previous studies. Our pigment data provide evidence for the lake-wide importance of picocyanobacteria and high interannual variation and spatial heterogeneity of phytoplankton in Lake Tanganyika, which may render difficult assessment of long-term changes in phytoplankton driven by climate change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.2005.01358.x
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  • 3
    Electronic Resource
    Electronic Resource
    Can a community of small-bodied grazers control phytoplankton in rivers? (1998)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 39 (1998), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Phytoplankton, zooplankton and grazing were monitored throughout the growing season for three years (1994–96) in the Belgian section of the River Meuse.2. A size structure analysis of the algal community shows that there was a summer shift toward larger algal units, following a decline in phytoplankton biomass. These changes occurred after an increase in zooplankton biomass and diversity.3. Daily filtration rates of grazers ranged from 1 to 113% day–1 and maxima were observed during the summer period. Higher rates tended to correspond with peaks of rotifer biomass. A decline in total phytoplankton biomass within two weeks followed the increase in zooplankton biomass and filtration rate. A rapid biomass recovery was then observed, along with a shift of the algal community toward larger units. When grazing activity was not sustained, due to zooplankton fluctuations, the change in phytoplankton size structure was less marked.4. We suggest that the composition of the phytoplankton community of large rivers may at times be controlled by grazers. However, such biotic interactions can take place only when physical constraints are reduced, i.e. when discharge is low, and when increased transfer time, high temperature and availability of grazeable algae allow high zooplankton biomass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1998.00258.x
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  • 4
    Electronic Resource
    Electronic Resource
    Relative importance of the trophic and direct pathways on PCB contamination in the rotifer species Brachionus calyciflorus (Pallas) (1995)
    Springer
    Hydrobiologia 313-314 (1995), S. 249-257 
    Details
    ISSN: 1573-5117
    Keywords: PCB ; rotifer ; trophic pathway ; Direct pathway ; Meuse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To determine the contribution of food ingestion (trophic pathway) to PCB contamination of zooplankton in the river Meuse (Belgium), we used 14C-labelled algae (Dictyosphaerium ehrenbergianum) to measure ingestion and assimilation rates in the rotifer species Brachionus calyciflorus. When the concentration of algae in the culture medium varied from 20 103 to 200 103 algal cells ml−1 (0.12 to 1.18 mg Cl−1), the Brachionus calyciflorus ingestion rate varied from 0.25 ± 0.12 to 1.52 ± 0.43 ng C ind−1 h−1 at 15 °C and from 0.74 ± 0.17 to 5.93 ± 0.61 ng C ind−1 h−1 at 20 °C. The assimilation efficiency (ratio of the assimilation rate to the ingestion rate) measured in a culture medium containing 200 103 algal cells ml−1 was 55.7 ± 5.8%. Since the PCB concentration measured in the phytoplankton of the river Meuse is about 3 µg PCBs g−1 D.W., the estimated PCB contamination of zooplankton ascribable to the trophic pathway ranges from 0.22 ± 0.17 to 1.31 ± 0.77 µg PCBs g−1 D.W. at 15 °C and from 0.64 ± 0.34 to 5.10 ± 2.10 µg PCBs g−1 D.W. at 20°C. The lower figure based on measurements effected at 20 °C is comparable to the actual level measured in zooplankton samples collected in the river Meuse (0.69 ± 0.20 µg PCBs g−1 D.W.). The applicability of the formula used in our estimate was checked in a 48-hour in vitro experiment in which the rotifers were fed contaminated algae. The PCB accumulation measured in the rotifers was found to coincide with the calculated PCB contamination. Additional experiments were carried out to determine the contribution of the direct pathway to PCB contamination of zooplankton living in the river Meuse (0.02 µg PCBs l−1 of water; average dissolved organic matter: 3 mg C 1−1). The PCB concentration in zooplankton resulting from direct uptake of PCBs from the water was estimated at 0.19 ± 0.05 µg PCBs g−1 D.W. These results show that in zooplankton living in polluted ecosystems, PCBs are likely to accumulate via the trophic pathway to concentrations up to 30 times higher than by direct contamination. Furthermore, our estimates of PCB contamination via the trophic pathway coincide quite well with actual concentrations measured in situ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00025957
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  • 5
    Electronic Resource
    Electronic Resource
    Lake Muzahi, Rwanda: limnological features and phytoplankton production (1993)
    Springer
    Hydrobiologia 257 (1993), S. 107-120 
    Details
    ISSN: 1573-5117
    Keywords: Lake Muhazi ; tropical lakes ; phytoplankton production ; fish production ; Rwanda ; Africa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Lake Muhazi, a small lake of Rwanda (East Africa) was studied from 1986 to 1990. A dramatic decrease of the catch of Oreochromis niloticus (350 T y−1 in the fifties vs 30 T y−1 in 1982) suggested a loss of productivity or overfishing. In the same period, other ecological changes occurred: the submerged macrophytes regressed and there was a decrease in Secchi depth (0.65 m in 1987 vs 1.5 m in the fifties). Compared to other lakes of the same area, the plankton production seemed low. The results of the present study characterize lake Muhazi as a shallow lake with a rather unstable diurnal stratification and with slight differences in mixing regime between its eastern, deepest part and its western, shallowest part. Secchi disk depth does not vary seasonally to a large extent. The water has a rather high mineral content (conductivity of about 500 µS cm−1 at 25 °C) and low concentrations of dissolved N and P, except in the hypolimnion, where NH inf4 sup+ -N can be high. Two species, Microcystis aeruginosa and Ceratium hirundinella, account for most of the phytoplankton biomass, which is about 50–80 mg chlorophyll a m−2 in the euphotic zone, usually with little seasonal variation. Daily gross production estimates amount to about 6 to 9.5 g O2 m−2 d−1 with a significant difference between the two parts of the lake. Data on C:N and C:P ratio in the phytoplankton suggest that some N deficiency might occur in the eastern part. Moreover, the Zm:Zc ratio could also lead to rather low net production rates (0.21–0.25 d−1 for a mixed layer of 4 m) In conclusion, the primary production of lake Muhazi is medium for African lakes and the hypothesis that decreased planktonic production could account for a reduced fish production should be discarded. Whereas the present yield of the fishery is only 20 kg ha−1 y−1, the yield estimated from primary production ranges between 46 and 64 kg ha−1 y−1. This could be reached through proper management. Finally, some hypotheses are given to explain the ecological changes which occurred in the lake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00005951
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  • 6
    Electronic Resource
    Electronic Resource
    Are phytoplankton dynamics in rivers so different from those in shallow lakes? (1994)
    Springer
    Hydrobiologia 289 (1994), S. 1-7 
    Details
    ISSN: 1573-5117
    Keywords: phytoplankton ; rivers ; shallow lakes ; turbulence ; turbidity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This paper introduces a series of contributions to the ninth meeting of the International Association of Phytoplankton Taxonomy and Ecology, held in Belgium during July, 1993. It draws from the original papers a synthesis which supports the view that the successful species in rivers and turbid shallow lakes are selected primarily on their ability to survive high-frequency irradiance fluctuations as they are circulated through steep light gradients. The selective distinction is less than that which discriminates between plankton of deep lakes and shallow lakes or even between clear and turbid shallow ones. River plankton is, however, dependent on fast growth rates but its survival in rivers is aided by a suite of water-retentive mechanisms. The ecology of turbid systems is dominated by physical interactions, those biotic interactions traditionally believed to regulate limnetic communities being suppressed and rarely well-expressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00007404
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  • 7
    Electronic Resource
    Electronic Resource
    Ecology of the phytoplankton of the River Moselle: effects of disturbances on community structure and diversity (1993)
    Springer
    Hydrobiologia 249 (1993), S. 111-116 
    Details
    ISSN: 1573-5117
    Keywords: phytoplankton ; river ; community composition ; disturbance ; diversity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A data set on community composition of the phytoplankton of the River Moselle (France) has been used for testing the ‘intermediate disturbance hypothesis’ (IDH). After a short presentation of the ecology of the river and of its phytoplankton, the main changes in composition and diversity of the suspended algal assemblage are described. It is emphasized that discharge fluctuations, related to weather changes, play a key role, but that biotic factors such as grazing and parasitism may also influence diversity in ‘stable’ summer conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00008847
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  • 8
    Electronic Resource
    Electronic Resource
    Foreword (1994)
    Springer
    Hydrobiologia 289 (1994), S. vii 
    Details
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00007402
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  • 9
    Electronic Resource
    Electronic Resource
    Impact of the Tihange nuclear power plant on the periphyton and the phytoplankton of the Meuse River (Belgium) (1984)
    Springer
    Hydrobiologia 119 (1984), S. 119-128 
    Details
    ISSN: 1573-5117
    Keywords: nuclear plant ; site study ; periphyton ; phytoplankton ; biomass ; diatom communities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A survey was made from 1976 to 1981 of the possible effects of Tihange nuclear power plant on the Meuse river. Phytoplankton and periphyton were affected only during low water flow. Both decreases and increases of biomass were recorded for phytoplankton but, for periphyton, only increases. The structure of diatom communities is affected downstream of the plant during low water flow, because sensitive species are replaced by more tolerant ones. In the reach downstream of the plant, the maximum observed temperature increase is 4.2 °C and the maximum decrease in dissolved oxygen is 15%. Except for these two parameters immediately below the plant, any changes observed cannot be attributed solely to the nuclear power plant, but rather to the combination of thermal effects with effluents from other industries which together contribute to the more significant changes observed further downstream.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00011951
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  • 10
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    Phytoplankton biomass and production in the river meuse (Belgium) (1987)
    Elsevier
    Details
    Publication Date: 1987-12-01
    Print ISSN: 0043-1354
    Electronic ISSN: 1879-2448
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Elsevier
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