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  • 11
    Electronic Resource
    Electronic Resource
    Reduction of Microcystis blooms in a hypertrophic reservoir by a combined ecotechnological strategy (1999)
    Springer
    Hydrobiologia 408-409 (1999), S. 31-38 
    Details
    ISSN: 1573-5117
    Keywords: eutrophication ; Microcystis ; reservoir restoration ; phosphorus precipitation ; carbon dioxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In Bautzen reservoir, a shallow, hypertrophic water in Eastern Saxony, biomanipulation led to structural changes in the phytoplankton community but did not reduce algal biomass. To supplement the top-down management, a new type of water treatment technology was tested during two seasons (May–August 1996/1997), aiming at the bottom-up control of mass developments of the cyanobacterium Microcystis aeruginosa.The technology is based on a combined lake–internal phosphorus precipitation and a transport of hypolimnetic water rich in free carbon dioxide into the upper layers. During the treatment periods, there were found both an increase of CO2concentrations in the mixed layer and an extension of the period in which free CO2was detected in the epilimnion. The concentrations of phosphorus could be lowered drastically in the whole water body. Microcystiswas almost totally suppressed (1996) or appeared with a delay (1997) compared to the regular annual pattern observed before the treatment. In contrast to the preceding year (1995), diatoms played a major role in the summer phytoplankton during the treatment years (1996/1997). The two application periods are compared with respect to the influence of meteorologically determined variables.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017097502883
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  • 12
    Electronic Resource
    Electronic Resource
    Predation by piscivorous fish on age-0 fish: spatial and temporal variability in a biomanipulated lake (Bautzen reservoir, Germany) (1999)
    Springer
    Hydrobiologia 408-409 (1999), S. 39-46 
    Details
    ISSN: 1573-5117
    Keywords: perch ; zander ; predation ; selectivity ; biomanipulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Predation by perch (Perca fluviatilisL.) and zander (Stizostedion luciopercaL.) on their new-hatched fish was studied in the littoral and pelagic zone in the biomanipulated Bautzen reservoir (Germany). Sampling was conducted from the middle of May to the middle of August in 1997. To investigate predation, we compared the littoral and pelagic zone, because the littoral zone could provide a refuge area for age-0 fish. This study focused on: 1. timing of predation, 2. selectivity of predation and 3. feeding pressures. In the littoral zone, age-1 perch fed first on age-0 percids at the beginning of June, when age-0 percids reached a mean length of 20 mm. Age-2 and older perch and zander started feeding on age-0 percids in the middle of June in both habitats. At this time, age-0 percids reached a mean length of 30 mm. In both habitats, species selective feeding on age-0 perch and age-0 zander was found. Most of the sampling time zander fed selectively on their own descendants. In general, mean lengths of age-0 fish found in the predator stomachs were smaller than those in situ. The strongest decrease of age-0 fish abundance started in both areas before percids began to feed on age-0 fish. In the middle of June, predation pressure on age-0 fish was higher in the pelagic zone, whereas in July and August it was higher in the littoral zone. After a strong initial decline due to unknown factors, age-0 fish abundance was controlled by piscivores. Predation started at the time when age-0 fish gape sizes were big enough to feed on large daphnids. As age-1 perch started first feeding on age-0 fish, at high densities they could be an important source of early mortality on age-0 zooplanktivores. This would be advantageous for the daphnid population in two ways, because the efficiency of two different predators would be reduced. Age-0 fish are consumed by age-1 perch, and age-1 perch feed on age-0 fish and not on daphnids. Consequently, the feeding behaviour of age-1 perch could be a key to achieve a stable long-term biomanipulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017049719721
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  • 13
    Electronic Resource
    Electronic Resource
    Phytoplankton responses to grazing by Daphnia galeata in the biomanipulated Bautzen reservoir (1998)
    Springer
    Hydrobiologia 389 (1998), S. 101-114 
    Details
    ISSN: 1573-5117
    Keywords: phytoplankton ; Microcystis aeruginosa ; grazing ; Daphnia galeata ; size shift ; biomanipulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We studied the response of phytoplankton to grazing by Daphnia galeata in the hypertrophic Bautzen reservoir (Dresden, Germany) from January 1995 to May 1996 during a long-term whole-lake biomanipulation experiment. The correlation between clearance rate of D. galeata and total phytoplankton biomass was negative only if biomass of Microcystis aeruginosa was excluded. This suggests that M. aeruginosa is the main grazing resistant phytoplankton species in the Bautzen reservoir. Except for M. aeruginosa and grazing-resistant Staurastrum quadridentatum spec. nov. (Scharf, 1995) no other phytoplankton species was able to reach a biovolume above 1 mm3 L-1 when the clearance rate of Daphnia exceeded 0.1 L L-1 d-1. There was significant positive correlation between mean cell or colony size of phytoplankters and clearance rate of D. galeata, showing an advantage of bigger cells or colonies at high grazing pressure. Cross-correlation indicated a time lag of about one month between changes in grazing pressure and a change in phytoplankton mean size. The phytoplankton species were divided into edible and inedible fractions, depending on their width and length. No edible species were able to reach high biovolumes during high biomasses of D. galeata but a positive correlation was found between the edible fraction of phytoplankton biovolume and the clearance rate of D. galeata. However, this relationship disappeared when the ‘ingestible edible’ fraction of M. aeruginosa was excluded, suggesting a rejection of ‘edible’ Microcystis colonies by D. galeata. A negative correlation was found between the inedible fraction of phytoplankton biovolume without M. aeruginosa and the clearance rate of D. galeata which might be due to superior competition of M. aeruginosa. We could clearly show that biomanipulation might not work well with respect to the reduction of total phytoplankton biomass under hypertrophic conditions and finally discuss a theoretical threshold of phosphorus (probably around 80 μg L-1), below which biomanipulation should become effective.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003531732222
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