'n Ondersoek na die rol van soöplankton in Roodeplaatdam

[摘要] English: Roodeplaat Dam is a warm monomictic and eutrophicwaterbody, which is situated in a summer rainfall area.A definite thermocline and hypolimnion are found insummer, together with a high primary production, whichgives rise to a large anaerobic hypolimnion duringsummer. The Pienaars River/Hartbees Spruit arm of the dam wasmuch more turbid than the Edendale Spruit arm and themain basin of the dam. Large water inflows duringsummer had a dilutionary effect on the electricalconductivity, nitrate, nitrite, and phosphate concentrations.High chlorophill values and dominance for extended periods by the blue-green algae, Microcystis and Anabaena, were indications of the degree of eutrophication in the dam.Five fish species were found in Roodeplaat Dam, of whichOreochromis mossambicus and Chetia flaviventris weredominant. The fry of these species are known to bepredators of zooplankton.Low total zooplankton biomass was found in summerbecause of decreased living space, due to a largeanaerobic hypolimnion. The high zooplankton numbersduring summer, in spite of low total biomass, resultedfrom a change of dominance from the large Daphnia spp.to the smaller Thermocyclops and Ceriodaphnia spp.There were marked increases in zooplankton numbers withthe change of· phytoplankton dominance from blue-greenalgae to green algae and cryptomonads.Twenty two zooplankton species in numbers warrantingexamination were found in Roodeplaat Dam.By the use of correlation coefficients, Cluster Analysisand correlation with environmental conditions, thezooplankton were separated into eight groups. The mostinfluential conditions governing the density ofzooplankton taxa in Roodeplaat Dam were those relatingto food type and temperature, and to a lesser extent pHand electrical conductivity.Thermocyclops oblongatus was present throughout thestudy period and dominated the zooplankton community.Extremely high annual p/B ratios of 82,63 and 88 werefound by two production-determination methods.Correspondingly an annual production of589,24 kgC.annum-1 was derived for thetotal zooplarikton population.In comparison with the zooplankton communities of otherSouth African systems, Roodeplaat Dam's zooplanktoncorresponded most closely with that of HartbeespoortDam, which is also a warm monomictic and eutrophicsystem.

[发布机构] University of the Free State