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rivers carrying water from land runoff to the sea. These 

 waterways range from the Mississippi River, which drains 

 41 percent of the conterminous land mass of the United 

 States, down to tiny trickles across a beach. The volumes 

 of water and sediment moved reflect not only the total 

 amount of precipitation and its annual cycle, but also 

 the sizes and slopes of drainage basins and the types of 

 soil over which the rivers flow. 



(5) Sedimentation . The general outlines of many estuaries, 

 lagoons, and embayments in the estuarine zo^e were formed 



by erosion from land runoff durinq the last ice age when 

 sea levels were much lower than they are now. As the sea 

 level rose, the drowned river mouths became zones of 

 mixing, sediment deposition, and erosion where the rivers 

 and tidal currents met. These erosion and sedimentation 

 processes molded the estuarine zone into its present shape 

 and continue to change it. 



(6) Climate . Solar energy striking the earth sets up 

 complex cycles of water and energy flow from the oceans to 

 the sky and the land and back again. That part of the 

 energy cycle occurring in the atmosphere gives rise to the 

 various combinations of weather phenomena which make up 

 local climates. Land, sea, and sky are mutually dependent 

 in producing specific climates, and the great ocean cur- 



