306 



nities, but the specific processes and causal relationships of complex 

 whole systems and interacting subsystems have only recently been 

 partially understood. 



Modification of estuarine ecological systems is nevertheless a trend 

 which can be qualitatively, if not quantitatively, observed. Figure 

 IV.6.1 indicates the general relationships between man's activities 

 and estuarine ecological system modification. 



The Nation's population and economy have expanded rapidly in the 

 recent past and will continue to grow substantially in the foreseeable 

 future. Moderate projections indicate a doubling of national popula- 

 tion by the turn of the century. Much of this growth, probably more 

 than one-third, will occur in the estuarine zone. Population growth 

 will spur the expansion of urban and suburban developments. Major 

 portions of urban development will develop along all major coastlines 

 of the United States — particularly the Atlantic coastline north of 

 North Carolina, Florida, the middle portions of the Gulf of Mexico 

 and California. The economy will also expand both in scope and diver- 

 sity to meet the demands of an increasing, wealthy population. Much 

 of this economic activity will be centered on or closely adjacent to the 

 Nation's estuaries and coastal shoreline. These economic activities will 

 vary from place to place due to the location of natural resources and 

 the demands for these resources, historic circumstance, availability 

 of markets and changes in technology. 



The general growth of both the population and economy is reflected 

 in expanding trends noted for more specific activities related to the 

 estuarine environment : marine fisheries, civilian and national defense 

 transportation, marine mining and processing, outdoor recreation and 

 waste discharge. All of these activities, as well as the associated second- 

 ary and marginal activities located in the estuarine zone, will intensify 

 in future years. Marine fisheries and outdoor recreation are highly 

 dependent upon naturally occurring properties of estuarine ecological 

 systems. Transportation, mining and waste discharge are much less 

 tied to these systems, although at some point in the continuum of degra- 

 dation these too would be adversely affected. 



The case has been made that although all of these activities vary 

 in their impact and dependence on estuarine systems, they all tend 

 increasingly to modify those systems in a multitude of ways. 



There appear to be at least three forms of estuarine system modifi- 

 cation common to the specific activities described above: waste dis- 

 charge, dredging, and construction of physical structures. In other 

 words, these activities, and many others, contribute significantly to 

 not only one identified form of estuarine system modification, but are 

 usually responsible for a number of alterations of the biophysical 

 environment. 



Although generalizations about the effects of man's activities on 

 estuarine ecology are hazardous at best, the following results generally 

 characterize the modifications associated with significant waste dis- 

 charges, dredging and filling, and construction of physical structures 

 either on fresh water inflows or in the estuaries themselves : 



(1) Productivity of biotic communities is generally reduced. This 

 is due to many factors including reduction or over provision of nutri- 

 ents, abrupt changes in temperatures and salinities, changes in circula- 

 tion patterns, and destruction of physical components of the system. 



(2) Species diversity and organization is simplified. 



(3) Trends toward severely modified ecosystems are established. 



J 



