A LIMNOLOGICAL RECONNAISSANCE 43 



ther decline to 2.23 cc. at 15 m. Thus the greater part of 

 the decrease took place in the upper half of the mesolim- 

 nion. 



The last item in table 21 shows the results obtained on 

 water from the well of the Lakeside Laboratory. This 

 water had a temperature of 11.3°. It will be noted that 

 there was an abundance of free carbon dioxide, about seven 

 times as much as was noted in the lake water at a depth of 

 33 m. It also contained almost two and a half times as 

 much fixed carbon dioxide as the surface water of the lake. 

 There was a fairly large supply of dissolved oxygen in this 

 well water; the result shown in the table is undoubtedly 

 too high since, in obtaining the samples, the water was ex- 

 posed to the air as it was being pumped into the bottles. 



A set of observations on the dissolved gases of lake Men- 

 dota was made on August 6, 1919, and the results are shown 

 in table 22. The epilimnion of lake Mendota showed the 

 same degree of alkalinity as that of West Okoboji lake, but 

 the lower water of the former had a distinctly larger 

 amount of free carbon dioxide. The epilimnion of lake Men- 

 dota possessed a smaller amount of fixed carbon dioxide 

 than West Okoboji lake, averaging about 5 cc. per liter less, 

 but the difference in the hypolimnion was not so marked. 

 The amount found at the bottom, 22 m., in the former lake 

 was the same as that at 15 m. and 20 m. in the latter, while 

 that at 15 m. and 18 m. in lake Mendota was the same as 

 that in the upper water of West Okoboji lake. Both lakes 

 belong to the "hard water" group, with the water of West 

 Okoboji lake carrying a somewhat larger quantity of car- 

 bonates in solution. 



A slightly larger amount of oxygen was found in the 

 upper water of lake Mendota but there was a distinctly 

 smaller amount in the hypolimnion than in West Okoboji 

 lake. 



