the geographical and pJiysiographic features of the terrain surround- 

 ing the water (or, in the case of a river, the land drained by it), all 

 have their bearing on the carbon dioxide content. 



Because of its crucial position in the lake's metabolism, a radical 

 unbalancing of the amount of carbon dioxide in solution is felt 

 throughout the entire biological cycle. A minimum amount will limit 

 the quantity of phytoplankton a body of water can support, as 

 indicated above in the remarks on Crystal Lake. A boundless 

 supply, together with other favorable conditions, may influence the 

 development of a superabundant water bloom, followed by a series 

 of disturbed biological conditions. Examples of this are to be 

 found in the prevalent water blooms in southern Michigan and 

 Wisconsin, in Minnesota, and in some northern Iowa lakes. Only 

 rarely have northern lakes been found with floras which approach 

 the bloom condition. In southern parts of Wisconsin, the richness of 

 the algal flora in the limestone region, as previously mentioned, is 

 related to a high bound and half-bound carbon dioxide content. 

 For example. Lake Geneva in Walworth County contains an average 

 of 20.7 ppm of calcium and 3.7 ppm of carbonates. Trout Lake in 

 Vilas County, a medium hard water lake, contains but 6.7 ppm of 

 calcium and no carbonates. This great difference in the amount of 

 available carbon dioxide is correlated with a great dissimilarity of 

 the floras. Lake Geneva has at times a dense bloom of the eutrophic 

 type, but in Trout Lake there is a relatively scant growth of algae in 

 the main body of water. Birge and Juday ( 1911 ) have shown that 

 there may be as many as 1000 phytoplankters per liter (mostly Oscil- 

 latoria sp.) at a depth of 15 meters in Lake Geneva At this level, 

 free oxygen was 2.4 ppm and the temperature was 13.6° C. It may 

 be of interest here to point out that the number of phytoplankters 

 may be as high as 9 million (filaments, not cells) per liter in hard 

 water lakes during periods when water blooms flourish (Prescott, 

 1932). 



Although an adequate supply of carbon dioxide is essential, an in- 

 crease in carbon dioxide tension, especially if rapid, may either kill 

 fish or seriously upset their physiology. Death is brought about more 

 or less directly through failure in elimination of carbon dioxide from 

 the body on account of the high concentration of carbon dioxide in 

 the water, or indirectly through ionization forming injurious car- 

 bonic acid ( Powers, Shields, and Hickman, 1939 ) . 



Again, the basic chemistry of a lake varies greatly as carbon diox- 

 ide is removed from the bicarbonates. Some Iowa lakes that I sur- 

 veyed developed a pH of 9.6-9.8 in the upper zones during the sum- 

 mer period of accelerated photosynthesis; an increase for the period 



[39] 



