Limnologie van de overstromingsmeren van de Rufiji rivier, Tanzania
Vervaeke, B. (2003). Limnologie van de overstromingsmeren van de Rufiji rivier, Tanzania. MSc Thesis. Katholieke Universiteit Leuven (KUL), Laboratorium voor Aquatische Ecologie: Leuven. 119 pp.
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Documenttype: Doctoraat/Thesis/Eindwerk
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| Abstract |
Nine lakes of the Rufiji River floodplain in Tanzania were investigated on water quality, macrophyte density, fish amount and zooplankton. This study is based on one survey in August 2002 after the major flood of that year. Also one isolated lake, Zimbwini, was investigated during this study. This lake is situated outside the floodplain. There are clear differences between the floodplain lakes in physical parameters, mainly due to differences in pH and Secchi-depth. Lake Mtanza had a significant lower oxygen-level than the other lakes. Conductivity was extremely high in Lake Umwe. Lakes Chemchem and Lungola had also a higher conductivity, but not that extreme. Except for Lake Mtanza, Lake Ruwe and Lake Weme, there were no differences between the pelagic and littoral zones within the lakes. The isolated lake, Zimbwini, differed particularly in temperature and oxygen level. Between the lakes there were also significant differences in chemical characteristics. Lakes Zumbi, Chemchem, Ruwe, Uba, Lungola and Zimbwini were clearly distincted from other lakes. This was based on their phosphorus and ammonia concentrations. Lake Chemchem had a much higher phosphorus and ammonia concentration. Less higher was the phosphorus concentration of Lake Ruwe. Lake Zumbi differd by the lack of ammonia. Macrophyte cover percentage was generally very low. This was probably due to overhanging trees which surrounded most of the lakes. Lake Umwe was the only floodplain lake that had a macrophyte cover of over 85%. The cover of the other lakes was less than 30%. Only the isolated lake had a higher macrophyte cover. Significant differences in chlorophyll concentration in the water were noticed. The extremes were found in Lake Mtanza (highest concentration) and Lake Umwe (lowest concentration). Also Lake Zumbi was significantly different in chlorophyll concentration. Zooplankton community within the floodplain lakes of the Rufiji River were mainly dominated by Copepods. Cladocera expressed a high variety in both composition and abundance between the lakes. However, there were no differences in densities of the zooplankton between the lakes (except for Lake Lungola). The amount of different taxa differed between the lakes. Secchi-depth had a negative effect on both total density and amount of taxa. Increase in pH meant an increase in density and number of taxa. Increasing macrophyte cover also meant an increase in number of taxa, but a decrease in total density. The further away from the Rufiji River, the lower the amount of taxa. Finally there was an increase in number of taxa with increasing lake surface area. The Shannon-Wiener diversity index H was mainly determined by characteristics of the lakes. The bigger the lake and the higher the cover of macrophytes, the higher H. On the contrary H decreased with distance from the river and the clarity of the lakes. The Simpson index D increased proportionally with the circumference of the lake and reversed proportionally with, again, the distance to the Rufiji River and the saturation level of oxygen. All lakes were significantly different in plankton community structure. species which occur in Zimbwini were not different from those in the floodplain. A distinction between pelagic and littoral zones based on the structure of the plankton community was only possible in Lakes Mtanza, Zumbi, Umwe and Zimbwini. This observation suggests that the zooplankton community in the lakes would not be significantly different without a periodical flood. Notice that diurnal and seasonal changes were not considered in this study. A more intensive study during all seasonal phases would allow us to formulate more founded statements about the possible consequences when the proposed dam at Stiegler’s Gorge is built. |
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