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wkh the gravitational attracition of the sun and the moon. The results 

 of this are the imique estuarine water movement patterns caused by 

 the differenceis in density between fresh river water and salt ocean 

 water, and the tidal ebb and flow which is noticeable only in the estua- 

 rine zone. 



All forms of life on earth depend on the sun as their ultimate source 

 of energy. Tliis energy is incorporated into plant material which in 

 turn supports all animal life. Plants need water and light to grow. 

 There is a profusion of both in the estuarine zone together with a 

 plentiful supply of dissolved nutrients derived from both land and sea. 

 These conditions make coastal areas the most productive environments 

 in the world, and as a result very specialized biological communities 

 have developed in the estuarine zone. Such communities cannot only 

 tolerate the dynamic balance of conditions but actually depend on the 

 constantly recurring environmental variations to sustain themselves. 



The wide range of interaction of the two basic driving forces of 

 gravity and solar energy brings about a bewildering variety of indi- 

 vidual environments in the estuarine zone, each being dominated and 

 controlled by a different combination of factors. Some may be domi- 

 nated by tidal range, some by river flow, some by geometry of the 

 coastline, some by climate, some by the sediments deposited, and some 

 by combinations of these. The variety is infinite. 



Yet, within this variety, there is order which lends itself to measure- 

 ment and through measurement to management of the estuarine zone 

 to preserve it for continuing multiple use. The purpose of this dis- 

 cussion is not to present a detailed analysis of the differences among 

 the parts of the estuarine zone, but rather to outline what these dif- 

 ferences are, why they exist, and what must be measured to establish 

 a basis for sound teclinical management within the overall framework 

 of wise institutional management. 



It would be convenient if the state of knowledge were such that the 

 estuarine environment and its variety could be described in terms of 

 the primary forces which control it ; then it would be possible to man- 

 age each estuarine system efficiently and exactly for optimum use. 



Unfortmiately, the present extremely limited state of knowledge 

 requires the measurement of a wide variety of attributes, and manage- 

 ment must be derived through the pragmatic application of knowl- 

 edge gained from such measurement. 



There are six different kinds of characteristics that should be under- 

 stood to make a rational effort at sound technical management : 



Shape and size. — Fresh water carries sediments eroded from the 

 land to the coast where they are deposited and molded along with the 

 original shoreline by the energy of ocean waves and currents. Shape 

 and size go far toward determining water movement, the life forms 

 present, and the speed with which pollutants can be absorbed or passed 

 through the estuarine zone. These are characterized by length of shore- 

 line, water and marsh area, and water volume. 



Water movement. — The slight difference in density between fresh 

 water and ocean, combined with tidal, weather, and shape effects, 

 causes diversity of water movement patterns in the estuarine zone. 

 These patterns are important in pollution control and in determining 

 the ecological balance. Parameters of water movement are river inflow, 

 tidal range, currents, density difference, and volume of tidal inflow. 



