89 



within which management must operate. In the fullness of time and 

 with greater understanding of the world it may be possible to modify 

 the environmental conditions to some extent, but for the present the 

 existing environmental limitations must be accepted.^ 



This discussion has so far considered only those environmental 

 factors which dominate the estuarine environment, not the environ- 

 ment itself. Management's fundamental concerns, however, are with 

 the appearance and quality of the individual environment and with 

 the variety and usefulness of the life forms a particular environment 

 will support. 



There are many life forms which exist throughout the estuarine 

 zone, most of them being particularly adaptable forms of plankton, 

 crustaceans, and fish. In addition to these, however, there are some less 

 adaptable life forms which require a limited range of conditions to 

 survive and yet others which need a very specific environment to 

 reproduce. 



Maine lobsters, for example, are numerous in the North Atlantic 

 estuarine region, scattered in the Middle Atlantic, and cannot be found 

 in other regions. The commercial shrimp, on the other hand, are 

 abundant throughout the Gulf, Caribbean, and South Atlantic regions, 

 but sparse beyond this range. Maine lobsters thrive in the cold Labra- 

 dor Current waters, while the major commercial species of shrimp need 

 warm waters like those of the Gulf Stream to reproduce. 



Within the general range of the regional estuarine environment are 

 specific local conditions with which management in particular estua- 

 rine systems must deal. The next part of this discussion considers local 

 conditions of land and water interaction and their relationship to the 

 living communities present. 



Section 4. The Land and the Water 



Nowhere on the earth's surface are land and water as intimately 

 related as in the estuarine zone, and nowhere are their interactions so 

 significant in the ultimate effect on man's environment. 



Concern with the quality of the environment is couched ultimately 

 in terms of its effect on life forms — -whether it is safe for human beings 

 to be near, whether it looks clean, and whether desirable aquatic life 

 forms can live and reproduce in it. These conditions are measured in 

 terms of the magnitudes of water quality parameters which tell in- 

 directly what the w^ater quality is. These magnitudes depend not only 

 upon the character and concentrations of waste materials, but also 

 upon the rapidity with which a particular system can purge itself of 

 damaging agents. 



The shape of land along the land-sea interface goes far toward deter- 

 mining what water movement and circulation patterns exist in partic- 

 ular local areas, and, consequently, how fast a particular estuarine 

 system will rid itself of pollutants. Within the estaurine regions dis- 

 cussed in the preceding section, different structural types define 

 patterns of water movement typical of particular structures, no matter 

 what the external environment may be. 



1 One environmental factor, river flow, is already being freely modified — sometimes with 

 less understanding than may be desirable. A case study on damages associated with river 

 flow modification in Charleston Harbor is presented in chapter 5 (IV-1-3). 



