Phosphorus dynamics in shallow eutrophic lakes: an example from Zeekoevlei,South Africa |
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Authors: | Supriyo Kumar Das Joyanto Routh Alakendra N. Roychoudhury J. Val Klump Rajesh Kumar Ranjan |
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Affiliation: | (1) Department of Geology and Geochemistry, Stockholm University, Stockholm, 10691, Sweden;(2) Department of Geological Sciences, University of Cape Town, Rondebosch, 7700, South Africa;(3) Department of Biological Sciences and Department of Geosciences, Great Lakes WATER Institute, University of Wisconsin-Milwaukee, 600 East Greenfield Avenue, Milwaukee, WI, 53204, USA;(4) School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, 110067, India |
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Abstract: | Zeekoevlei is the largest freshwater lake in South Africa and has been suffering from hyper-eutrophic conditions since last few decades. We have used total P (TP), dissolved phosphate (PO4 3−), organic P (OP), calcium (Ca) and iron (Fe) bound P fractions to investigate the relevant physical, chemical and biological processes responsible for sedimentation and retention of P and to study phosphorus (P) dynamics in this shallow lake. In addition, redox proxies (V/Cr and Th/U ratios) are used to study the prevailing redox conditions in sediments. Adsorption by CaCO3 and planktonic assimilation of P are found to control P sedimentation in Zeekoevlei. Low concentration of the labile OP fraction in surface sediments restricts the release of P by bacterial remineralisation. Low molar Ca/P and Fe/P ratios indicate low P retention capacity of sediments, and P is most likely released by desorption from wind-induced resuspended sediments and mixing of pore water with the overlying water column. Handling editor: J. Saros |
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Keywords: | Phosphorus Primary productivity Lake Sediment Dredging |
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