In-lake concentration changes of phosphorus (P) and nitrogen (N) in lakes Vättern, Vänern, Mälaren, and Hjälmaren in response to diminished input has been examined from the mid-1960s onwards. In the former two deep and oligotrophic lakes with slow water renewal, drastic reductions in P-input from the middle of 1970s caused just minor reductions in P-concentration over a very long time. At the same time accumulation occurred in the water mass of inorganic N and possible reasons are discussed. In the latter two mesotrophic to hypertrophic lakes, two shallow basins in L. Hjälmaren showed slow recovery due to release of P from sediments. The same basins and two basins in L. Mälaren have suffered from N-deficiency, particularly during the pre-phosphorus reduction years, and nitrogen fixation was indicated. In two L. Mälaren basins recovery of in-lake P concentrations was better than expected in comparison to the so-called IMSA-model for lake recovery from nutrient pollution. In the other five lakes/basins chlorophyll concentrations after 20 years were similar compared to those modeled.
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1 December 2001
Recovery from Eutrophication: Experiences of Reduced Phosphorus Input to the Four Largest Lakes of Sweden
Anders Wilander,
Gunnar Persson
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AMBIO: A Journal of the Human Environment
Vol. 30 • No. 8
December 2001
Vol. 30 • No. 8
December 2001