THE USE OF COPPER SULPHATE FOR ALGAL CONTROL 

 AND ITS BIOLOGICAL IMPLICATIONS^ 



By JOHN B. MOYLE 



FISHERIES RESEARCH UNIT, MINNESOTA DEPARTMENT OF 

 CONSERVATION, ST. PAUL, MINN. 



Inteoduction 



During the last 40 years coppers sulphate (CuSO^.SHoO) has been 

 used widely and effectively for the control of objectionable algal growths 

 in lakes and reservoirs. This salt is also poisonous to fish and aquatic 

 invertebrates. However, experimental work (Moore and Kellerman 1905; 

 Marsh and Robinson 1910; Ellis 1937) and the general observations of 

 many field workers show that usually plankton algae can be destroyed 

 with concentrations below those toxic to aquatic animals. 



Most users of copper sulphate and investigators like those already 

 cited have been principally concerned with the comparative toxicity of 

 the salt to different animals and plants and with the immediate practical 

 results of algal control. To the conservationist there is another and a 

 wider viewpoint which is worthy of consideration. Evaluation of algal 

 control with copper sulphate in terms of immediate toxicity or in terms 

 of sanitary or esthetic gain is not enough. The long-time effect of repeated 

 copper sulphate treatments on the biological productivity of a water, espe- 

 cially on fish production, should also be taken into account. In an increas- 

 ing number of lakes algal growths are being controlled for such reasons 

 as elimination of obnoxious odors, improving conditions for swimming 

 and maintaining the value of shore property. For these waters, considera- 

 tion of the effect of copper sulphate on fish production is essential. Many 

 municipal water supplies also are used for public fishing. In these recrea- 

 tional values should not be overlooked. 



Growth of most objectionable algae can be controlled with concentra- 

 tions of copper sulphate between .12 and .50 ppm. Fish, on the other hand, 

 tolerate considerably greater amounts. In a Minnesota hard-water lake, 

 concentrations as great as 1.2 ppm have been used without damage to a 

 mixed game and rough fish population. Surber (1943) reports that 2 ppm 

 copper sulphate did not kill small-mouth bass in hard-water ponds. Much 

 higher local concentrations have been used for snail control in hard waters 

 without fish loss (McMullen 1941) and Nichols et al. (1946) found that 

 in the hard water of Lake Mendota (alkalinity about 170 ppm) the lethal 

 concentration for large-mouth bass was ''about 200 parts of applied copper 



* Investigational Report No. 76, Fisheries Research Unit, Minnesota Department of 

 Conservation, St. Paul. 



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