with this distribution is the first graph to the right, which shows the 

 amount of bound carbon dioxide that occurs in the lakes ( expressed 

 in parts per miUion). As would be expected, since the majority have 

 a pH above neutral, most of the lakes have a relatively high bound 

 carbon dioxide content in the form of calcium and magnesium car- 

 bonates. In the particular group of lakes under consideration the 

 bound carbon dioxide content was no higher than 14 ppm, however. 



The graphs on the right of this diagram show the distribution of 

 green and blue-green algal species ( expressed in percentages of the 

 lakes' total algal flora). It will be noted that where both the bound 

 carbon dioxide and the pH are high the percentages of blue-green 

 and green species are approximately equal. With a lowering of the 

 pH and a corresponding decrease in the amount of bound carbon 

 dioxide, however, there is an increase in the percentage of green 

 algal species, reaching 100 per cent of the flora in the highly acid 

 lakes. This increase is in almost exact inverse proportion to the 

 decrease in the carbon dioxide content. In this connection it should 

 be pointed out that there is no causal relationship between large 

 numbers of individuals or numbers of species and high bound car- 

 bon dioxide content since in this form it is unavailable to most vege- 

 tation. Bound carbon dioxide content is significant, however, and is 

 useful in providing an index of algal production, because almost in- 

 variably a lake with a high bound carbon dioxide content will also 

 be high in bicarbonates. Half-bound carbon dioxide in Ca( 003)2 

 and MgCa( 003)2 is available to photosynthetic organisms, and it 

 follows that such lakes are able to support an abundant algal flora, 

 other factors being also favorable. Whereas the relationship between 

 half-bound and bound carbon dioxide mentioned above usually 

 holds, it is possible in senescent lakes to have a high bound carbon 

 dioxide content with little or no half-bound or free carbon dioxide. 

 In such cases one would expect to find a very scanty algal flora and 

 a heavy deposition of marl or some similar carbonate. See Welch 

 ( 1935 ) for an outline of the relationship between available carbon 

 dioxide and bicarbonates. 



In Figures 5 and 6, the lakes used in this analysis are divided into 

 four groups: hard water drainage (HD), soft water drainage (SD), 

 hard water seepage (HS), and soft water seepage (SS). In Figure 5 

 the distribution of the hard and soft water drainage lakes according 

 to pH readings is shown in the graph on the left. With this distribu- 

 tion is compared bound carbon dioxide content, as in Figure 4. As 

 was noted in Figure 4, the blue-green and green algae are present in 

 almost equal percentages in the hard water lakes; the acid lakes have 

 by far the larger percentage of green algae and almost no blue-green 



[30] 



