Lake restoration. Why oxygenation and artificial mixing cannot substitute for a decrease in the external phosphorus loading |
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| Authors: | René Gächter |
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| Institution: | 1. Swiss Federal Institute for Water Resources and Water Pollution Control (EAWAG) at Swiss Federal Institute of Technology (ETH), CH-6047, Kastanienbaum
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| Abstract: | Data obtained from Lakes Baldegg and Sempach, two artificially mixed and oxygenated lakes, show that it is technically possible to significantly improve redox conditions, even in large eutrophic lakes. It is discussed why - the well-known release of phosphorus from anoxic sediments does not necessarily result from an abiotic reduction of phosphorus containing iron compounds, - net phosphorus retention by sediments is not simply linearly related to the phosphorus content of a lake, - artificial oxygenation of a previously anoxic hypolimnion does not permanently increase phosphorus retention capacity of lake sediments. From this it is concluded that improvement of hypolimnic redox conditions by lake internal measures such as aeration or oxygenation may accelerate the rate of recovery induced by a reduction of the external phosphorus loading, but that oxygenation per se will hardly be able to cause a reduction of trophic state. |
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