11 



THE BIOPHYSIOA-L ESTUARINE REGIONS 



Each estuarine system along the coastline is affected to some extent 

 by all of these dominating environmental factors. In some cases the 

 dominance of one particular factor is readily apparent. It is much 

 more often the case that the competing environmental factors are so 

 evenly balanced that none can be said to dominate and the estuarine 

 zone appears to be composed of a bewildering variety of unique 

 systems. 



Yet, the dominating environmental factors listed above form a set 

 of natural guiding principles which govern the general characteristics 

 of the estuarine zone of the United States, and the occurrence of vari- 

 ous combinations of these environmental factors permits the grouping 

 of the national estuarine system into 10 geographical zones, each gov- 

 erned by a different combination of environmental conditions (figure 

 IV. 1.19). 



Characteristics of the Biophysical Regions 



North Atlantic estitarine region: Canadian horder to Cape Cod 



Cool, fertile waters with a large tidal range strike a steep, indented 

 coast with deep water close inshore, but protected from the full force 

 of the ocean waves by a wide continental shelf. Moderate precipitation 

 with heavy snowfall leads to heavy spring river runoff which domi- 

 nates local circulation. Natural erosion and sedimentation are not 

 severe problems, and the evolution of drowned river valley estuaries 

 is in an early stage in this region. 



ngmlV.I.I9 

 BIOPHYSICAL REGIONS OF THE UNITED STATES 



