lakes are higher than those for hard water drainage or soft water 

 seepage types. This suggests that if other essential nutrients were 

 present, the soft water drainage lake might be more productive. 

 High nitrogen content is correlated seasonally with a low plankton 

 count, for when the plankton is high, especially during summer 

 months, the nitrogen content of the lake water is low, increasing, 

 however, as the biota decreases in fall and winter. In many seepage, 

 acid lakes (Lynx and Mary Lakes, Wisconsin, for example), the 

 desmid flora has an abundance approaching that of bog lakes, which 

 are highly productive. 



Soft Water Seepage Lakes 



In Table 6 three typical hard water drainage lakes are compared 

 with three soft water seepage bodies. The latter type of lake usually 

 has a sandy bottom, with few bays and shallows; the nutrients are 

 low in concentration and the half -bound carbon dioxide content is 

 much less than in the drainage lake. In soft water habitats the algal 

 flora is almost entirely planktonic, and even this is relatively scant. 

 Filamentous algae are practically non-existent. In many such lakes, 

 only sterile Mougeotia and Zygnema can be found, entangled about 

 the cuhns of rushes that form sparse beds. Zooplankton is scarce in 

 the soft water lakes, which further explains their general low produc- 

 tivity of fish. The total plankton residue (dry weight analysis) in 

 Crystal Lake, Wisconsin, is only 0.48 mg. per liter (Birge and 

 Juday ) . When a soft water lake is found capable of supporting a sub- 

 stantial fish population, it is obvious that at least periodically there 

 must be crops of phytoplankters of sufficient magnitude to support 

 the intermediate zooplankton elements of the food chain. The pro- 

 portionate production of fish in a soft water lake has been made very 

 graphic in a paper by Juday ( 1942 ) . One of his diagrams is shown 

 in Figure 3. This illustrates the quantitative relationships of the sev- 

 eral components of the biota as expressed in kilograms per hectare of 

 lake surface (wet weight, ash-free computation). See also Table 7 

 for analyses of 27 soft water seepage lakes. 



One of the many interesting problems involved in the differences in 

 production of soft and hard water lakes is the role played by hetero- 

 trophic bacteria. The unanswered question is: Do the nature and 

 abundance of the biota determine the kind and quantity of the bac- 

 terial flora, or does the bacterial flora function critically in releasing 

 nutrients which, if sufficient, make possible an abundant and varied 

 algal flora through the overturn of organic matter? This is doubtless 

 a vicious circle, but Henrici and McCoy ( 1938 ) and Henrici ( 1939 ) 

 have shown that soft water, oligotrophic lakes have fewer bacteria 



[23] 



