10 



PROBLEMS OP LAKE BIOLOGY 



Qeographic Location 



Human 

 Influence 



Longitude . 

 ^Altttu 



Seuaie 

 A^ricultiire 

 ^Alining 



Bothm \ Precipitation Wind Insolation 

 Conformation 



Heat Penetroiion OxygenPenetr Developmentj>f Seasoned Cycle 

 5tr.mcahon ^ Utiir/ahon '-'^'"^^ '^'J?"'" ^d'ri^f^fUS^" 



Trophic feature of the Lake 



Amount, eoniposi'tionaitd distribution of 

 plants and animals . Also 

 rates of circulation. 



Productivity 



Fig. 1. A chart suggesting the interrekitions of factors affecting the metabolism of a lake. 



numerous exceptions these conclusions ap- 

 pear to be substantially correct. Str0ni 

 (1928) and others believe that the relation 

 of water volume to extent of surface and 

 bottom is the most important factor in the 

 development of eutrophy. Mean depth, 

 being a direct indication of this relation, 

 becomes a significant index. 



It is not to be expected, however, that a 

 single measure will provide a sure index of 

 eutrophy and oligotrophy. Probably the 

 greatest number of the exceptions in this 

 case will be due to the edaphic factor. 



Thus, if a drainage area provides insuffi- 

 cient nutritive salts, a shallow lake maA' be 

 prevented from developing eutrophy. On 

 the other hand, a deep lake may become 

 somewhat eutrophic if supplied with un- 

 usual amounts of nutritive materials. Such 

 exceptions provide practical problems but 

 do not detract from the value of the original 

 thesis. 



The area of a lake also affects its metabo- 

 lism in a number of ways, most directly 

 perhaps through its effect on exposure to 

 wind and consequently on water circula- 



