Factors controlling primary production in a hypertrophic lake (Hartbeespoort Dam, South Africa) |
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Authors: | Robarts Richard D |
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Institution: | National Institute for Water Research, CSIR PO Box 395, Pretoria 0001, South Africa |
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Abstract: | The physical factors controlling algal primary production weredemonstrated from data collected for a hypertrophic lake. Amaxranged between 12.4 and 5916 mg C m3 h1. Arealrates ( A) varied between 46.9 and 3381 mg C m2 h1.The factors permitting and controlling production were subjectivelyseparated into two categories. In category 1, nutrients (N +P), which were in overabundance, permitted large standing cropsof Microcystis aeruginosa to develop (>1000 µg chla 11). Wind patterns determined the dramatic spatialand temporal changes in algal standing crop which could dropto 2.7 µg chl a 11. In category 2 were the factorswhich affected the rate processes. The buoyancy mechanism ofMicrocystis usually kept the alga in the euphotic zone. A powerrelationship (r = 0.92, n = 54) between A and Amax/ min showedthat with increasing phytoplankton vertical stratification,Amax was increasingly important in the integral. The saturationparameter IK and photosynthetic capacity were temperature dependent.Variations of A were significantly related to changes in watercolumn stability (g cm cm2) because both axes of thephotosynthesis depth-profile were affected by stability changes. |
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