96 



MAN ON THE LANDSCAPE 



FIG. 50. Pollution of the most vicious variety. In this collection of dead fish, 

 many species are represented, carp being' most common. When the durable carp 

 dies, the pollution is indeed severe. Most pollution has no such obvious result 

 as this. Usually the better fish move out if they can, or die young 1 , or are un- 

 able to reproduce. The water quietly, slowly becomes barren of valuable species. 



Toxic chemicals introduced into streams or bodies of water kill or 

 discourage aquatic plant life, which is the basis of aquatic animal life, 

 which is of great value to man. (Fig. 50.) 



Siltation: Many water power reservoirs, stock ponds, water con- 

 servation pools, navigation pools, and natural or artificial lakes of 

 recreational value have been and are being rapidly filled with silt. 

 This is caused primarily by denudation and erosion of the water- 

 sheds, which in turn is caused by ignorance or carelessness in the 

 biologic management of the land. The U. S. Department of Agricul- 

 ture has made a study of 20 power reserviors along the south Appala- 

 chian fall line which have filled completely with silt in an average of 

 30 years each, some in as little as 20 years. (Fig. 51.) The cause was 

 determined to be erroneous land use with its resulting erosion. 

 O'Shaugnessy reservior on the Scioto River above Columbus, Ohio, 

 was reported in the same study to have a use expectancy of 145 years, 

 due to its less hilly and less eroding watershed. 8 Even this situation 

 is far from satisfactory to Columbus since the capacity of this water 

 supply reservior is shrinking while the city is growing. This situation 



8 U. S. Department of Agriculture, Siltation of Reservoirs, 1940, pp. 139-140. 



