IV-71 



Nearshore ocean surface salinities are stronqly Influenced by river 

 runoff and local precipitation. The effects of the Mississippi on 

 the Gulf of Mexico are shown 1n Figure IV. 1.29. Less dramatic, 

 but nonetheless significant, are the effects of the Hudson on the 

 Atlantic and of the Columbia on the Pacific. 



The turbidity of ocean water 1s generally low except where it meets 

 the shore; there the amount of turbidity 1s a direct reflection of 

 the Intensity of wave action and the nature of bottom material. 



Dissolved oxygen is essential for all aquatic life. The amount of 

 dissolved oxygen present in surface ocean water is very close to the 

 total amount the water can contain. Since this saturation concentra- 

 tion depends on both temperature and salt concentration, the warm, 

 saline waters of the Gulf contain far less oxygen than the cold, 

 relatively fresh waters off the Alaskan coast. 



The natural quality of water free from human impact in the rivers 

 entering the estuarine zone depends primarily on the nature of the 

 ground over which they flow. Minerals enter the water by dissolving 

 from soil and rock as the water flows over it or carries 1t along. 

 Water flowing over limestone or other sedimentary material usually has 

 greater concentrations of dissolved minerals than water flowing over 

 volcanic rock and sand. Insoluble minerals are carried along as 

 sediments, some dissolving slightly and others settling out in quiet 

 reaches of the rivers or in the estuarine zone. 



