IV-4yb 



systems, although at some point in the continuum of degradation 

 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 modi- 

 fication common to the specific activities described above: waste 

 discharge, dredging, and construction of physical structures. In 

 other words, these activities, and many others, contribute signif- 

 icantly 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 discharges, dredging and filling, and construction of physical 

 structures either on fresh water inflows or in the estuaries 

 themsel ves : 



(1) Productivity of biotic communities is generally 

 reduced. This is due to many factors including 

 reduction or over provision of nutrients, abrupt 



