The Plankton Algae of the Palisades Interstate Park 125 



gradual adoption of filtration for municipal water supplies interest 

 in algicides has decreased, and the literature of the past decade con- 

 tains but few references on the subject. 



The following discussion of the method is based in large part 

 upon a study of the literature rather than actual experience, since 

 the Park lakes produced but one " bloom " which required treatment 

 ■during the summer of 1918, and this was composed of a single 

 organism. Although the copper sulphate method is simple in theory- 

 it is complicated in application since it rests upon variable factors. 

 Attention has been repeatedly called to the fact that each lake must 

 be studied as an individual and the use of copper sulphate controlled 

 by preliminary studies of the particular body of water to be treated. 

 The variable factors that should be investigated in each individual 

 case are: the volume of the lake, the particular organisms to be elimi- 

 nated, the temperature of the water, the organic matter in solution, 

 the temporary hardness of the water, and the amount of dissolved 

 carbon dioxid. 



The computation of the volume of water should rest upon accurate 

 hydrographic maps which show, by means of contour intervals, the 

 depths in the various portions of the lake. Birge and Juday ('14) 

 recommended the formula of Penck for computing the volume of 

 the different strata on a hydrographic map. In this formula .?i is 

 the area of the upper surface, Sn the area of the lower surface of 

 the section whose volume is to be determined, and h the vertical thick- 

 ness of the stratum. The volume of the stratum {V) then is 



V=^- (s,-fs.+ VsT%). 

 3 



This computation must be repeated for each contour interval, and 

 the total volume of the lake obtained by combining those of the 

 different strata. A rougher method for approximating the volume 

 of a lake is given by Whipple ('14), who states that an acre of water 

 three feet deep represents a million gallons of water. The approxi- 

 mate volume in millions of gallons may be calculated by multiplying 

 the acres of surface by the average depth of the water and dividing 

 by three. This, of course, involves making a number of soundings 

 to determine the average depth of the lake. 



Thermal stratification of deep lakes is a common occurrence in 

 summer. In the warmer upper epilimnion there is a vertical circula- 

 tion of water, but in the lower colder hypolimnion no circulation 

 takes place. The region of transition between the two is quite sharp, 

 and cases have been reported by Birge and Juday ('ii) of a drop of 

 5 to 8 degrees Centigrade in a depth of tw'O meters at the point of the 

 thermocline. Investigations by Goodnough ('05) on Jamaica Pond 

 at the time of thermal stratification have shown that two days after 

 an application of copper sulphate at the rate of 1/2,000,000, the cop- 

 per sulphate content of the epilimnion was several times that of the 

 hypolimnion. If, therefore, the lake to be treated has a marked 

 thermal stratification the computation of the volume of water to bs 

 treated should include only the epilimnion and thermocline and not 

 the hypolimnion. 



