SIDE EFFECTS OF 58 YEARS OF COPPER SULFATE TREATMENT OF THE FAIRMONT LAKES,MINNESOTA1 |
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Authors: | Mark J Hanson Heinz G Stefan |
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Institution: | 1. Senate Counsel to the Agricultural and Natural Resources Committee, Minnesota State Senate, and Research Fellow, St. Anthony Falls Hydraulic Laboratory, 605 Portland Avenue, No. 4, St. Paul, Minnesota 55102.;2. Professor and Associate Director, St. Anthony Falls Hydraulic Laboratory, University of Minnesota, Mississippi River at 3rd Avenue S.E., Minneapolis, Minnesota 55414. |
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Abstract: | The shallow Fairmont Lakes in southern Minnesota have been treated with copper sulfate for 58 years to reduce excessive algal growth. Copper sulfate was applied to five lakes at cumulative rates upo to 1647 kg/ha (1470 1b/acre), totaling 1.5 million kilograms. Data collected since treatment of the Fairmont Lakes began in 1921 provide alarming insights into lake responses to sustained chemical treatment with copper sulfate. Short-term and long-term effects have occurred. Short-term effects include: a) the intended temporary killing of algae, b) dissolved oxygen depletion by decomposition of dead algae, c) accelerated phosphorus recycling from the lake bed and recovery of the algal population within 7 to 21 days, and d) occasional fish kills due to oxygen depletion or copper toxicity or both. Long-term effects are shown to include: a) copper accumulation in the sediments, b) tolerance adjustments of certain species of algae to higher copper sulfate dosages, c) shift of species from green to blue-green algae and from game fish to rough fish, d) disappearance of macrophytes, and e) reductions in benthic macroinvertebrates. The conclusion is that while copper sulfate treatments enjoy great popularity because they kill and remove algae almost instantaneously, other immediate or cumulative side effects can be harmful to many other aquatic organisms. |
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Keywords: | lakes eutrophication lake management lake restoration toxicity lake ecosystems copper sulfate |
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