108 



PROBLEMS OF LAKE BIOLO(iY 



have resulted from geologic agents that 

 have caused the deposition of the finer 

 sediments. In those regions of glacial scour 

 the former type of lake is common, and the 

 vegetation in these lakes is usually very 

 scarce. In regions of glacial dissipation 

 the lake basins are usually constructed of 

 drift materials. Here the vegetation is 

 much more abundant. This also may be 

 true of lakes of non-glacial origin that 

 possess finer sediments. 



It has been aptly stated that a lake be- 

 gins to die immediately after it is born. 

 Thus sedimentation enters into the develop- 

 ment of lakes, and determines the soils, the 

 color of the water, the abundance of elec- 

 trolytes, the hydrogen-ion concentration, 

 and the quality and quantity of the vege- 

 tation in them. 



The diagram below is suggested as an 

 example of lake development and the ac- 

 companying physio-chemical changes. This 

 scheme is the result of observations on more 

 than 200 lakes in northern Wisconsin, and 

 a complete discussion is shortly to be pub- 

 lished. 



Classification of Lakes with Respect to 

 THE Rooted Hydrophytes 



To construct an entirely satisfactory 

 classification of lakes, that can be widely 

 applied with respect to the rooted hydro- 

 phytes, is very difficult and probably should 

 not be attempted until much more work is 

 completed. There are possible classifica- 

 tions that consider one or more factors such 

 as origin, structure, geography, and mor- 

 phology, but it is soon apparent in nature 

 that many of these factors occur in com- 

 binations which make it difficult to compare 

 lakes of one region with another without 

 involving elaborate descriptions. 



A classification of use to workers in 

 aquatic plant ecology must consider the 

 dynamic factors of lake development, and 

 these must be well enough understood to 

 enable one to trace them from one lake to 

 another, and from one region to another, 

 in order that the dynamic nature of aquatic 

 plants may be determined. These factors 

 are closely related, and the part played by 



the plants in the sedimentation of lakes is 

 an important one. When a large number 

 of lakes are examined they show properties 

 that characterize them as one type of lake 

 or another, for example clear water, sandy 

 soils, and sparse vegetation, or turbid water 

 rich in phytoplankton and rooted hydro- 

 phytes, or brown water, organic soils, and 

 little vegetation. These lake types have 

 received the names oligotrophic, eutrophic, 

 and dystrophic, respectively, and they serve 

 well in rough descriptive work on the 

 rooted aquatic plants. This classification, 

 however, does not give a complete repre- 

 sentation of the dynamics of plant ecology 

 for any one locality, much less for widely 

 separated regions. Within regions where 

 hundreds of lakes are present one en- 

 counters many intermediate types, and 

 parts of large lakes may belong to all three 

 types. The very fact that all three types 

 may occur in a single lake is indicative of 

 lake development, and the use of these 

 terms is very convenient in describing the 

 character of a lake or portion of it. 



Pearsall (1920, 1921, 1929) in several 

 papers has used the terms "primitive" and 

 "evolved" lakes, and has shown that the 

 vegetation is distinctive in each. He 

 further shows that they are dynamic in 

 their development and that evolved lakes 

 have developed from primitive lakes by silt- 

 ing. 



The AA^'isconsin Geological and Natural 

 History Survey has for a number of years 

 used the terms drainage and seepage in 

 describing the lakes of Wisconsin. This 

 classification though incomplete in its mor- 

 phological description appears to have the 

 advantage in that many physical, chemical, 

 faunal, and floral characteristics can be pre- 

 dicted for lakes when information pertain- 

 ing to the drainage system is known. For 

 example, a lake belonging to a drainage 

 system is often eutrophic in character, 

 while a seepage lake in Wisconsin is seldom 

 of this type, but usually oligotrophic, or 

 dystrophic in character. The seepage lakes 

 of Wisconsin, and the Middle West in gen- 

 eral, are located in kettle holes of pitted 

 outwash plains, or in moraines. They have 



