Yahara River system, but water blooms occasionally develop in it. 

 The average number of individuals per liter of lake water for the 

 Chlorophyta, the Cyanophyta, and the diatoms are listed in Table 3. 

 These figures were obtained by counts from centrifuged plankton 

 samples from Lake Mendota, Wisconsin, a typical hard water drain- 

 age lake. It will be noted that it is only in the months of May, June, 

 and July that the Chlorophyta exceed the Cyanophyta in numbers 

 per liter. It is interesting also to note that the numbers represent 22 

 species of Chlorophyta, only 6 species of Cyanophyta, and 15 species 

 of diatoms. This is a more nearly equal distribution of species among 

 these three groups of algae than usually occurs in a hard water 

 drainage lake when sedentary or attached species, as well as plank- 

 tonic forms, are considered. 



Hard Water Seepage Lakes 



This type of lake is rarely found in our region, for seepage lakes 

 are characteristically soft. Spider and Round Lakes, Vilas County, 

 Wisconsin, are examples. Sloughs which have no outlet and some 

 swampy ponds might be included in this class. Characteristics of 

 hard water seepage lakes are shown in Table 4. These habitats, as 

 might be expected, are not unlike the northern hard water drainage 

 lakes except that the chlorophycean flora equals or exceeds the cyan- 

 ophycean in abundance. Although the pH of the water in such lakes 

 was found to be always above neutral, it is likely that great varia- 

 tions would be discovered if readings were made throughout the 

 year. A much higher pH would be expected in late summer months 

 because of increased photosynthetic activity which removes the half- 

 bound carbon dioxide from the bicarbonates. 



Euglenoid genera, such as Phacus, Euglena, and Trachelomonas, 

 and some of the Chrysophyta, Tribonema spp. and Synura uvella, 

 for example, are typical components of the algal flora in hard water 

 seepage lakes. 



Soft Water Drainage Lakes 



Soft water lakes are nearly always of the seepage type; a soft 

 water lake with drainage, or a seepage lake with hard water, is sel- 

 dom found. It will be noted in Table 5 that soft water drainage lakes 

 have limnological and biological characteristics very similar to the 

 soft water seepage type. The algal flora, in both quality and quantity, 

 is predominantly chlorophycean. The phytoplankton is sparse, some- 

 times lacking except for an occasional diatom. It is noteworthy also 

 that the available total-nitrogen readings for soft water drainage 



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