A LIMNOLOGICAL RECONNAISSANCE 37 



supply of heat and of wind were such as to add 4° to the 

 temperature of each stratum below 10 m. (the temperature 

 m.-lO m. remaining as in the 1916 series), the work 

 would rise only to 2561 g. cm. — an amount which would 

 seem within the limits of the capacity of Okoboji. Under 

 these conditions the summer heat-income would be only 

 24,690 caL, a small gain over 1916 or 1550 cal. for 581 g. cm. 

 of work. Apparently, therefore a summer heat-income of 

 about 24,500 cal. is a maximum for lake Okoboji. This in- 

 come would involve a mean temperature of 24° for the water 

 of the lake, and this would imply a mean temperature of 

 about 20° for water in the 15 m.-40 m. region of the lake. 

 The distributing agencies seem theoretically able to effect 

 this. But it would require a rare conjunction of delivery 

 of heat and efficiency of distribution to secure results much 

 greater than those recorded in 1916. 



Systematic study of the lake, therefore, is required to 

 show whether temperatures even higher than those of 1916 

 are attainable in lake Okoboji. Such speculations as that 

 just given have very little value, but they may be per- 

 missible in the case of a lake so exceptional as Okoboji. 

 The possibilities of life in the lower water of such a lake 

 are profoundly influenced by these exceptional possibilities 

 of temperature, and the lake therefore offers chances for 

 unusual problems in the ecology of the plankton as well as 

 similar problems in the physics and chemistry of lakes. 



V. DISSOLVED GASES 

 West Okoboji lake belongs to the temperate tjT)e in which 

 there are two circulation periods and two stratification 

 periods each year; these periods correspond in general to 

 the four seasons of the year. The water is in complete 

 circulation for a time in the spring and again in the autumn, 

 but it is in a state of stratification in summer and in win- 

 ter. During the periods of complete circulation the tem- 

 perature of the water is substantially uniform from surface 

 to bottom and the dissolved substances are practically the 

 same at all depths; but during stratification the water of 

 the upper and lower strata show important thermal and 



