COPPER SULPHATE IN ALGAL CONTROL AND IMPLICATIONS 85 



ponds because "they take up nutrient materials and light that would 

 otherwise produce algae." 



A few general observations have been made on algal control and the 

 growth of larger aquatic plants. Huff (1923) notes that concurrent with 

 algal control in Lake Vadnais there was "cutting and removal of great 

 quantities of submerged vegetation each year." Domogalla (1935) states 

 that during 11 years of treatment of Lake Monona "weeds have grown 

 luxuriantly in 18 feet of water" and flourished despite the use of a 

 weed cutting machine. 



It appears that control of plankton algae with copper sulphate can 

 be expected to have little or no detrimental effect on larger aquatic plants 

 and may even increase their growth. 



Acquired Tolerance of Algae to Copper Sulphate 



Hale (1942) and Whipple (1927) are both definitely of the opinion 

 that algae do not acquire a tolerance to copper. However, acclimatization 

 of other microorganisms to copper and similar heavy metals is fairly well 

 known (Heilbrun 1937, p. 294). 



In the Fairmont lakes, Aphanizomenon seems to have acquired an 

 increased tolerance to copper as a result of 26 years of treatment. These 

 lakes were first treated in 1921 by Huff (1922). He carefully noted the 

 kinds of algae present, the concentrations of copper sulphate used and the 

 results. The concentrations used for successful control in the 4 lakes at 

 that time were: Amber, .15 ppm; Hall, .14 ppm; Budd, .20 ppm; and 

 Sisseton, .24 ppm. In the period 1943-46 much higher concentrations were 

 necessary to obtain the same results; the average of treatments in these 

 years being Amber, .35 ppm; Hall, .73 ppm; Budd, .80 ppm; and Sisseton, 

 .50 ppm. Two to five times as much copper sulphate must now be used as 

 was necessary in 1921. 



The high concentrations used in later years on the Fairmont lakes 

 were necessary and not due to calculation or judgment errors of the Fair- 

 mont Water Department. Moyle and Wilson (1946) supervised treatment 

 of Hall Lake with .5 ppm and achieved only partial success in eliminating 

 Aphanizomenon — a reduction of 1,200,000,000 to 21,800,000 filaments per 

 100 liters 5 days after treatment. This alga made a rapid recovery and 

 it was soon necessary to treat the lake again. In both 1921 and 1946 the 

 boat and burlap bag method of application was used. 



Two other hard-water Minnesota lakes with Aphanizomenon blooms 

 were treated for the first time in the summer of 1947. No filaments were 

 found following treatments with .3 ppm in Little Elk Lake, Sherburne 

 County, and no return of the bloom for a month was noted in Spring Lake, 

 Scott County, which was treated with .11 ppm. 



Summary 



Although much work has been done on the toxicity of copper sulphate 

 to different aquatic plants and animals, little consideration has been given 



