826 



ANIMALS AND THEIR ENVIRONMENT 



Table 16. A COMPARISON OF A SINGLE MAIN RIVER RESERVOIR PLAN 

 \VI I n A PLAN FOR MULTIPLE SMALLER HEADWATERS RESERVOIRS 



MAIN 



STREAM 



RESERVOIR 



MULTIPLE 



HEADWATERS 



RESERVOIRS 



Number of reservoirs 



Drainage area, square miles 



Flood storage, acre feet 



Surface water area for recreation, acres 



Flood pool, acres 



Bottom farm land inundated, acres 



Bottom farm land protected, acres 



Total cost: 



From E. P. Odum: Fundamentals of Ecology. 



less, destroys a smaller amount ot productive farm land, impounds more 

 water and is more effective in controlling floods and soil erosion. The 

 management of the fish population in the lakes created by large dams 

 is more difficult than the management of a pond. Sport fishing is usually 

 very good when a dam has first been built, but gradually the silting up 

 of the reservoir and the decrease in productivity change the nature of 

 the fish community from game fish to less desirable catfish and shiners. 

 The three chief sources of stream pollution are industrial materials 

 which are either directly toxic themselves or which reduce the oxygen 

 supply in the water, sewage and other materials which decrease the 

 oxygen content of the water and introduce bacteria and other septic 

 organisms (Fig. 40.2), and turbidity due to soil erosion in the watershed. 

 As the silt settles out downstream it may cover up the spawning grounds 

 of fish and have other direct deleterious effects. Erosion can be pre- 

 vented by proper soil management, industrial wastes can be prevented 

 by suitable design of the manufacturing process, and properly treated 

 sewage can be emptied into a stream without deranging its ecologic 

 relations. 



372. Marine Fisheries 



The primary productivity of the sea, as measured by the pounds of 

 organic carbon produced per year per acre of surface, is very high. The 

 productivity of the western Atlantic off the coast of North America is 

 2.5 to 3.5 tons of organic carbon per acre and that of Long Island 

 Sound is 2.5 to 4.5 tons per acre. The productivity of the average forest 

 is about one ton per acre, most cultivated land fixes only about three- 

 quarters of a ton of organic carbon per acre, and only the rich, in- 

 tensively cultivated cornfields of Ohio produce as much as 4 tons per 

 acre. Despite this high productivity, man's actual harvest from the 

 ocean, in terms of pounds of fish caught per acre of surface, is very low. 

 Only the rich fishing grounds of the North Sea produce as much as 15 

 pounds of fish per acre. The ecologic reasons for this are clear: the fish 

 are secondary or tertiary consumers and are on top of a vast "pyramid 

 of protoplasm." There are many organisms competing for the food 



