Hard Water Drainage Lakes 



These lakes are numerous and are to be found in such drainage 

 systems as the Wisconsin River, the St. Croix River, the Fox River, 

 and the Yahara River in Wisconsin, and in the Crooked River and 

 Cheboygan River in Michigan. In general, they are high in calcium 

 and half -bound carbon dioxide (see Table 1) and correspondingly 

 have a high pH (pH 7.2-9.4), Reference has aheady been made to 

 this type of lake and its characteristics. In southern Michigan and 

 Wisconsin, most drainage lakes are naturally harder than in the 

 northern parts of the states because of the difference in the chemis- 

 try of the soil. It is noteworthy that when the drainage type of lake 

 in the highland region has a sandy bottom, and few flat beaches 

 or shallow bays, it may be as poor a producer as some of the soft 

 water lakes. In Table 1, 13 hard water drainage lakes are listed to 

 show something of the quality of their algal floras in relation to 

 critical limnological features. Compare Table 1 with Table 2, 

 which summarizes collections made in Wisconsin from December 

 through July. 



These general quantitative and qualitative observations contribute 

 to the evaluation of the hard water lake as an habitual producer of 

 blue-green and diatom floras which are rich both in number of spe- 

 cies and in number of individuals. Chlorophycean species, on the 

 other hand, while not always fewer in number than the components 

 of the cyanophyte-diatom flora, comprise but a small portion of the 

 bulk of algal vegetation in hard water lakes. Except for the Volvo- 

 cales, they seldom, if ever, form water blooms. Certain members of 

 the Volvocales, Volvox and Pandorina, in some lakes may reach cli- 

 maxes that form blooms, though of relatively short duration. 



Drainage prevents hard water lakes from achieving a constantly 

 high concentration of nutrients; yet the chemistry of the water, 

 together with such eutrophic features as shallowness and high sum- 

 mer temperatures, make possible the characteristic luxuriant flora. 

 This type of lake may also have a high productivity of larger aqua- 

 tic vegetation — Sweeny Lake in Oneida County and Lake Mendota 

 in Dane County, Wisconsin, and Ocqueoc Lake in Presque Isle 

 County, Michigan, for example. 



Although there is conflicting evidence regarding the role that 

 phosphorus plays as a controlling factor in the development of 

 aquatic floras, many critical studies indicate that it is a regulator. 

 It is well known that soluble phosphorus in a lake decreases with 

 the seasonal increment in plankton and increases as organisms die 

 and disintegrate. Tressler and Domogalla (1931) have shown that 

 in Lake Wingra (Wisconsin) soluble phosphorus declines and 



[15] 



