44 Interrelationships of Fishes and Lake Habitats 



applied to lands may later appear in streams draining these lands,^^ and 

 the total phosphorus content of the stream water may vary from 10 to 

 nearly 200 ppb.* Without considering the extent that land fertihzation 

 may have influenced the phosphorus and nitrogen content of drainage 

 water from southern Wisconsin land, Sawyer ^^ estimated tlie relationship 

 between the nitrogen and phosphorus content of biologically treated 

 human sewage and this drainage water. Treated human sewage supplied 

 about 6 pounds of nitrogen and 1.2 pounds of phosphorus per person per 

 year, and the wastes of 750 persons were equivalent to the agricultural 

 drainage of one square mile of land area in southern Wisconsin on the 

 basis of nitrogen; similarly, treated wastes of 212 persons were equivalent 

 to drainage from the same area on a phosphorus basis.^^ 



Phosphorus was proved to be the most important item in the pro- 

 ductivity of water.-^' ^- With the greatly increased use of detergents, 

 which are largely complex phosphates, alkyl benzene sulfonates, and other 

 surface active agents, the problems associated with the discharge of 

 effluents from sewage plants, even where processing is complete, have 

 become at least twice as great as they were previous to the beginning of 

 the wide use of these detergents. Because of them, smaller amounts of 

 sewage effluents will cause greater fertilization of aquatic habitats than 

 formerly. It has been suggested that chemical methods may eventually 

 be used to remove a part of the phosphates from sewage effluents. ^- 



While alkyl benzene sulfonate is not very toxic to warm-blooded verte- 

 brates,-^^ concentrations greater than 1 to 2 ppm are toxic to sensitive fish 

 and aquatic organisms, ^^ and excessive phosphates and nitrates may 

 stimulate algal blooms to the extent that much of the esthetic value of a 

 water area may be lost. Moreover, the fish population is subjected to 

 constant danger, due to the fact that a sudden die-off of the algae might 

 result in a severe oxygen deficiency or in the actual poisoning of the fish. 

 These aspects of lake fertilization are discussed further in Chapter 6. 

 Needless to say, pollution may create real nuisance problems and even 

 dangers in the management of fishes in artificial lakes as well as in the 

 navigation pools of large rivers. 



pH AND CHEMISTRY OF WATER 



No attempt will be made here to describe variations in the mineral 

 content of impounded waters found throughout North America; rather 

 we are interested in waters containing abnormal amounts of certain 

 chemicals picked up from contact with natural deposits of minerals. As 

 is to be expected, the mineral composition of pond or lake water is 



* Parts per billion. 



