GASES IN WATERS OF WISCONSIN LAKES. 



1277 



hundred small lakes. About 60 

 in this region have been studied 

 that the month of August and 

 critical period for the distribu- 

 tion of gas in lakes, and that 

 from observations made at this 

 time the general history of a lake 

 may be inferred when the cycle 

 is known in detail from a num- 

 ber of lakes which may serve as 

 standards. The lakes of north- 

 eastern Wisconsin contain, in gen- 

 eral, soft water, the carbonates 

 being much lower than in the 

 southeastern lakes — frequently 

 not more than one-sixth as great 

 and not infrequently less than 

 one-tenth. 



The lakes in the northwestern 

 district are scattered in two some- 

 what ill-defined elongated seiies 

 extending north and south for a 

 distance of 70 miles or more. 

 Between 50 and 60 of these lakes 

 also have been examined. Their 

 water is intermediate in character 

 between that of the two other 

 districts, the content in carbon- 

 ates averaging nearly one-half 

 as great as that of the south- 

 eastern lakes. 



of the more important and deeper lakes 

 during the summer. The survey has found 

 the early part of September represent the 



Cb 

 CT N 34 36 38 40 



„2 2 4 6 8 10 12 14 16 Id 20 22 



2 

 3 



'5 



9 



lo- 

 ll - 

 12 

 13- 

 14- 



15- 



16- 



17- 



18- 



19- 



20- 



21 



22- 



CT 







N 



Cb 



Fig. 2. — Lake Mendota. Vertical distribution of gases, carbonates, 

 and temperature. January 26, 1906. C, carbon dioxide; Cb, carbon- 

 ates of lime and magnesia; N, nitrogen; O, oxygen; T, temperature. 

 See footnote. 



GASEOUS CHANGES IN LAKE MENDOTA. 



WINTER. 



Let me begin my account by a short sketch of the cycle of changes in Lake 

 Mendota. Figure 2 shows the condition under the ice in early winter. The 



free from the monocarbonates. Since, in the lakes of southeastern Wisconsin, the amount of dissolved 

 carbonates is considerable, the numeration of the horizontal scale is interrupted in order not to make 

 the diagram too large. For instance, the numbers at the top of figure 2 change abruptly from 22 to 34. 

 The larger numbers refer solely to the line Cb, indicating the number of cubic centimeters of COj 

 represented in the monocarbonates. A similar arrangement will be seen in other diagrams. 



The points at which observations were taken are indicated by small circles in the lines of the dia- 

 grams. The lines are drawn directly from one point of observation to the next, no attempt being 

 made to round off the curves. 



