26 Nature of Aquatic Environment 



that deltas are built and hills eroded. Water is the 

 chief factor in all those eternal operations of flood and 

 floe by which the surface of the continent is shaped. 



Transparency. — Water has many properties that fit 

 it for being the abode of organic life. Second only in 

 importance to its power of carrying dissolved food 

 materials is its transparency. It admits the Hght of 

 the sun; and the primary source of energy for all 

 organic life is the radiant energy of the sun. Green 

 plants use this energy directly; animals get it in- 

 directly with their food. Green plants constitute 

 the producing class of organisms in water as on land. 

 Just in proportion as the sun's rays are excluded, 

 the process of plant assimilation (photosynthesis) is 

 impeded. When we wish to prevent the growth of 

 algae or other green plants in a reservoir or in a spring 

 we cover it to exclude the light. Thus we shut off 

 the power. 



Pure water, although transparent, absorbs some of 

 the energy of the sun's rays passed through it, and 

 water containing dissolved and suspended matter 

 (such as are present in all natural water) impedes 

 their passage far more. From which it follows, that 

 the superficial layer of a body of water receives the 

 most light. Penetration into the deeper strata is 

 impeded according to the nature of the water content. 

 Dissolved matters tint the water more or less and give 

 it color. Every one knows that bog waters, for 

 example, are dark. They look like tea, even like very 

 strong tea, and like tea they owe their color to their 

 content of dissolved plant substances, steeped out of 

 the peaty plant remains of the bog. 



Suspended matters in the water cause it to be turbid. 

 These may be either silt and refuse, washed in from 

 the land, or minute organisms that have grown up in 



