open water, or a quotient of 5.0 when this is compared with 

 2,599,320 in the total bottom count. 



The activity of bacteria produces food substances for bottom or- 

 ganisms, as previously mentioned, and at the same time increases the 

 concentration of nutrients available for plant and animal life in the 

 upper levels. It is obvious that the quantity and quality of the bac- 

 teria in both bottom and open water floras can produce effects in 

 the chemical nature of the water, and in the chemistry and physical 

 condition of the bottom sediments. In a sense a closed cycle is in- 

 volved here. In the first place a rich bacterial flora, through the rapid 

 breakdown of organic matter, may produce (at least indirectly) a 

 varied and rich phytoplankton and zooplankton. The quantity and 

 quahty of the microbiota, in turn, have far reaching effects on the 

 productivity of other kinds of animal life, both on the bottom and 

 in open water. And finally, the relative abundance and quality of the 

 organisms (i. e., productivity) within a lake determine whether the 

 bottom sediments will support a rich bacterial flora. The role of 

 bacteria in this cycle has been clearly summarized by Waksman 

 (1941). 



The characteristic paucity of nutrients in a seepage lake is explain- 

 able, at least in some instances, by the source of the water, which 

 percolates through sand and crystalline soils. Frequently there is 

 seepage from bogs and marshes, with the result that the water is 

 rich in humic acids. Birge and Juday found only 3-4 grams of or- 

 ganic matter per cubic meter in the soft water type of lake; of this 

 amount, 15-18 per cent was accounted for by the plankton. Over a 

 three-year period they found that the total nitrogen content of such 

 a lake averaged 7.2 per cent of the dry weight of the plankton per 

 cubic meter of water ( as determined by ash-free analyses ) . 



Table 7 lists 27 typical soft water seepage lakes with their biota 

 and critical limnological features. 



Acid Bog Lakes 



The acid bog lake, usually found in Sphagnum bogs, is of the 

 kettlehole type. The water is at times acid, although the marginal mat 

 may be more acid than the open water. Here are found a great vari- 

 ety of desmids and a few Cyanophyta, such as Scytonema ocelhtum, 

 Hapalosiphon pumilus, and Chroococcus Prescottii. The plankton 

 of these lakes is not abundant, usually, but the filamentous forms 

 are luxuriantly developed, especially in the marginal waters and 

 in the small seeps leading into the lake. Such bodies of water are 

 aging rapidly, and there is a great accumulation of organic matter, 



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