Phytoplankton dynamics in a shallow, hypertrophic reservoir (Lake Blankaart, Belgium) in relation to nutrients and zooplankton
Geenens, V.; De Schuijmer, C.; Declerck, S.; Sabbe, K.; Muylaert, K.; Vyverman, W. (1998). Phytoplankton dynamics in a shallow, hypertrophic reservoir (Lake Blankaart, Belgium) in relation to nutrients and zooplankton. Biol. Jb. Dodonaea 65: 147-148 In: Biologisch Jaarboek (Dodonaea). Koninklijk Natuurwetenschappelijk Genootschap Dodonaea: Gent. ISSN 0366-0818, more Also appears in:Beeckman, T.; Caemelbeke, K. (Ed.) (1998). Populations: Natural and manipulated, symposium organized by the Royal Society of Natural Sciences Dodonaea, University of Gent, 29 October 1997. Biologisch Jaarboek (Dodonaea), 65. Koninklijk Natuurwetenschappelijk Genootschap Dodonaea: Gent. 257 pp., more |
| Keywords | Aquatic communities > Plankton > Phytoplankton
Aquatic communities > Plankton > Zooplankton
Conferences
Nutrients (mineral)
Water bodies > Inland waters > Water reservoirs
Belgium [Marine Regions]
Fresh water |
| Authors | | Top | - Geenens, V.
- De Schuijmer, C.
- Declerck, S., more
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| Abstract | Lake Blankaart is a shallow lake situated in western Belgium. During the last century, the lake turned eutrophic mainly due to sewage discharge and intense agriculture in the catchment-area. In 1994, lake Blankaart was dredged in an at tempt to restore its former state, i.e. a clear-water system dominated by aquatic vegetation. In order to evaluate the effects of this operation and the potential success of biomanipulation measures, phytoplankton species composition and seasonal dynamics were investigated from March 1996 to June 1997. The relationship between the observed trends and selected environmental factors, including nutrient concentrations and zooplankton, was studied in detail. Although nutrient concentrations have decreased since 1994, they are still comparable to those in other hypertrophic systems. However, nitrate concentrations have increased. Chlorophyll a content is still comparable to the pre-dredging conditions. In spring 1996, phytoplankton community is characterised by a pronounced succession of species, with biomass peaks of Bacillariophyta (Stephanodiscus hantzschii-complex, S. medius), Chlorophyta (Dictyosphaerium pulchellum var. pulchellum), Cyanobacteria (Gloeocapsa minor) and Cryptophyta (Cryptomonas sp. 1) respectively. During summer, Chlorophyta (Eutetramorus tetrasporus, E. fottii, Pediastrum-species, Closterium limneticum var. limneticum) constitute the most important taxonomical group. Biomass of Bacillariophyta, Cyanobacteria and Cryptophyta increases again during autumn. In spring 1997, the chlorophyte Dictyosphaerium pulchellum var. pulchellum and the cyanobacterium Planktothrix agardhii are the main contributors to total biomass. Diatoms (mainly Stephanodiscus medius) are less important in 1997. Species composition and seasonal trends in 1996 and 1997 were typical for eutrophic and hypertrophic lakes (Reynolds 1996). The observed large inter-annual variability in phytoplankton composition and dominance can as yet not be explained. Ordination analyses indicated that both physical and chemical factors, and especially nitrate, explain a large part of the variation in the phytoplankton data (up to ± 40 % ). In addition, 34 % of the variation could significant I y be related to zooplankton. However, the independent contribution of zooplankton is considerably lower (about 15 % ) when the effect of the physical and chemical parameters is partial- led out, indicating that although both bottom-up (nutrients) and top-down (zooplankton) processes influenced phytoplankton species composition during the study period, the influence of the latter is less pronounced. This might be related to the predominance of small zooplankton (especially Bosmina longirostris), which are known to be less efficient grazers than larger species such as Daphnia sp. In conclusion, it can be stated that the phytoplankton communities in lake Blankaart are still typical for eutrophic aquatic systems, despite the dredging activities in 1994. |
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