IV-69 



waters; 1n stratified systems, however, the small amounts of 

 minerals entering 1n the fresh water may be as Important 1n some 

 parts of the estuarlne zone as the much larger concentrations from 

 the sea are In others. The Interface between fresh and salt water 

 1s a region of complex chemistry where some material may be pre- 

 cipitated out or otherwise changed, much as lye soap used to be 

 "salted out" when soap was made by boiling lard with wood ash extract 

 in the backyard. Organic matter from decaying vegetation 1s partic- 

 ularly susceptible to this type of chemical effect. 



Climate also plays a direct role 1n determining estuarine water 

 quality. Excessive evaporation can drive salinities far above those 

 of ocean water, as in Laguna Madre, and create an inverse estuarine 

 system. Sunlight beating down on shallow embayments may raise 

 temperatures so high that use of the estuarine waters for cooling 

 may be seriously Impaired. 



Table IV. 1.8 summarizes ocean and river water quality 1n each of the 

 estuarine regions. Ocean water quality Itself varies 1n different 

 areas off the coast, generally reflecting ocean currents and climate 

 as discussed earlier. Ocean temperatures reflect not only the varia- 

 tion 1n latitude, but also the temperature differences of the cold 

 and warm currents around the coast. The temperature difference north 

 and south of Cape Hatteras 1s particularly striking, because the Gulf 

 Stream and Labrador Current water each dominate on one side of the Cape. 



