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Please use this identifier to cite or link to this item: http://hdl.handle.net/10204/725

Title: Cyanobacteria-phytoplankton dynamics of a hypertrophic African lake
Authors: Zohary, T
Pais-Madeira, AM
Robarts, RD
Hambright, KD
Keywords: Haartebeesport dam
Species composition
Microcystis aeruginosa
Oocystis lacustris
Competitive exclusion
Issue Date: 1995
Publisher: Pergamon-Elsevier Science Ltd
Citation: Zohary, T, et al. 1995. Cyanobacteria-phytoplankton dynamics of a hypertrophic African lake. Water Science and Technology, vol. 32(4), pp 103-104
Abstract: Phytoplankton species composition and abundance were recorded weekly or biweekly for nearly 7 years in a hypertrophic lake ( Hartbeespoort Dam, South Africa), together with a range of physical and chemical parameters. A total of 73 species were recorded, of which only 20 were occasionally abundant, and only 5 became dominant (>50% of total biomass) at least once (Microcystis aeruginosa, Oocystis lacustris, Aulacoseira (= Melosira) granulata, Cyclotella meneghiniana, Carteria cordiformis). The earlier years of the study (1982-1986) were drought years characterized by low water levels (10-15 m below the level at full supply), excess supply of nutrients at all times of the year, and overwhelming dominance of Microcystis aeruginosa. This K-selected species proved to be well adapted to withstand the range of environmental conditions throughout summer, fall and winter but it declined in spring each year when a fast successional episode followed. Several small-celled chlorophytes, diatoms and cryptophytes appeared and disappeared until Oocystis lacrustris became dominant for a few weeks, to be replaced by M. aeruginosa early in the summer. During the following rainy years (late 1986 to 1988), the lake re-filled. Major washout losses, concomitant with a considerable decline in surface water phosphorus concentrations and elevated TN/TP ratios, apparently led to the reduction in the abundance of M. aeruginosa. Its bloom extended over a smaller portion of the year in 1986 and 1987, and disappeared in May 1988, permitting the development of a more diverse phytoplankton community subject to control by 2ooplankton grazing. This long-term phytoplankton record from Hartbeespoort Dam demonstrates the key role of a dominant species in controlling community composition and diversity in hypertrophic lakes. Stable environments lead to low-diversity and high-biomass phytoplankton assemblages dominated by K-strategists, while disruptions of suitable strength and frequency allow for the development and maintenance of higher species diversity.
Description: Copyright: 1995 Pergamon-Elsevier Science Ltd
URI: http://hdl.handle.net/10204/725
ISSN: 0273-1223
Appears in Collections:Pollution and waste
Water resources and human health
General science, engineering & technology

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