COPPER SULPHATE IN ALGAL CONTROL AND IMPLICATIONS 83 



treatment. In the Fairmont lakes, it appears that the removal of such 

 an excess has had little effect on the yield of rough fish. Expressed another 

 way, organic production has not been reduced below, or much below, the 

 critical optimum level despite a long history of copper sulphate treatment. 



There are several reasons why such a result might be expected. First, 

 waters which have objectionable algal crops are very fertile and produce 

 an abundance of other aquatic life besides specific bloom formers. Second, 

 destruction of an algal crop by copper sulphate does not destroy the organic 

 material that this crop represents. The organic material is released into 

 the water upon decay of the algal cells. Often this decay is accompanied 

 by a great bacterial increase (Whipple 1927). Third, usually following a 

 copper sulphate treatment, rapid growth is made by copper tolerant forms 

 which were not killed. After the destruction of a heavy Aphanizomenon 

 bloom in Hall Lake on June 3, 1946, the population of planctonic diatoms 

 and green algae rose from 300,000 to 41,000,000 per 100 liters in 5 days. 

 During this same period, the population of animal plankters and euglenoids 

 rose slightly from 34,000 to 40,000 per 100 liters (Moyle and Wilson 1946). 



Schoenfeld (1947) concludes that since copper precipitates from hard 

 water as insoluble copper carbonate, this salt accumulates on the bottom 

 to the detriment of fish-food animals living there. This conclusion is evi- 

 dently based on the work of Nichols et al. (1946) on the accumulation of 

 copper in the treated lakes at Madison, Wisconsin, and the statement of 

 Hasler (1947) that Lake Monona, a treated lake of this chain, had 800 

 bottom fauna organisms per square meter in contrast to 9,000 for untreated 

 Lake Mendota. 



It is well known that copper carbonate is poisonous to snails and its 

 toxicity is utilized for controlling swimmer's itch. McMullen (1941) found 

 that when high concentrations of copper sulphate or mixtures of copper 

 sulphate and copper carbonate were applied to the shallow waters in Michi- 

 gan, "crayfish, leeches, tubificides and insect larvae were usually killed." 

 He also notes that the use of 20 ppm copper sulphate resulted in the ac- 

 cumulation of 78.6 mg of copper per square foot of bottom 4 hours after 

 treatment. 



It is certain from this and other similar observations by McMullen 

 and also from the experimental work of Whipple (1927) that following 

 a copper sulphate treatment, copper does precipitate onto the bottom mud. 

 It is also certain that high concentrations of precipitated copper are 

 poisonous to aquatic invertebrates. There is, however, an important ques- 

 tion to be answered. Do these precipitated copper compounds remain 

 insoluble and accumulate on the lake bottom to such an extent that pro- 

 duction of fish food is affected? 



Whipple (1927) noted that copper carbonate may be decomposed into 

 copper ''hydrate" (hydroxide?) and carbonic acid, and that although the 

 hydrate is insoluble, the carbonate is slightly soluble in the presence of 

 carbonic acid. Since carbon dioxide is being continually generated from 

 bottom muds, it is likely that at least some of the precipitated copper car- 



