2l6 



BULLETIN OP THE BUREAU OF FISHERIES. 



tion in the amount of heat as stated in terms of units of surface area. The upper 20 

 m. of these lakes contains 75 to 80 per cent of the total quantity of heat, and the reduced 

 thickness of this stratum in Cayuga Lake is nearly 14 per cent less than in Seneca Lake. 

 (See Table 3 .) The slightly higher temperature of the stratum in Cayuga Lake is not great 

 enough to compensate for this difference in thickness (cf. Birge and Juday, 19 14, p. 574). 



A longer series of years would undoubtedly change the figures stated above. But 

 it is not probable that such a series would greatly alter them or that it would change 

 the general relations of the heat income of the several lakes to each other. The smaller 

 lake has the smaller income, largely because of its thinner epilimnion. Cayuga Lake 

 has less heat than Seneca, largely because of the smaller ratio between maximum and 

 mean depth. The differences are not so great but that the series of budgets overlap, 

 the largest heat income of Canandaigua being larger than the smallest of Cayuga, and 

 Cayuga's series overlapping in a similar way that of Seneca. The largest heat income 

 in the series is that of Seneca in 1914, nearly 38,000 cal. 



Table 2 also shows the distribution of heat to the three thermal regions of the 

 lakes. The epilimnion contains about 60 per cent of the summer heat income, ranging 

 from 53 to more than 70 per cent. This stratum, together with its thermal depend- 

 ency, the thermocline, contains from 70 to nearly 90 per cent of the heat. Thus in Seneca 

 Lake, which may be nearly 200 m. deep, a surface stratum occupying little more than 

 the upper one-tenth of the depth contains from three-fourths to nine-tenths of the heat 

 accumulated from the sun during the season. 



Table 3 shows the distribution of the summer heat income by 10 m. intervals. 

 It shows the same facts as Table 2 but in another form. It makes especially clear the 

 small amount of heat which can be carried to considerable depths. In Canandaigua 

 Lake, for example, the total quantity of heat transmitted below 50 m. during the season 

 does not exceed the quantity delivered to the surface in one summer day ; and even in 

 the much larger and deeper Seneca Lake it does not exceed two days' supply. 



Table 3. — Distribution op Temperatures and of Calories of Summer Heat Income. 



[Note. — R. T.=reduc€d thickness of stratum in meters; T.= temperature in degrees centigrade; Cal. =calories of s umm er heat 

 income, i. e. , gain of heat above 4°; P. ct. =per cent of heat income in stratum.] 



CANANDAIGUA LAK8. 



