12 



Middle Atlantic estuarine region: Cape Cod to Cape Hatteras^ 

 exclusive of Chesapeake Bay 



A wide, gently sloping continental shelf with a smooth shoreline is 

 cut by the entrances of several major river systems carrying moderate 

 amounts of sediments. The same cool, fertile waters as in the North At- 

 lantic estuarine region wash this coastline but with a smaller tidal 

 range. The evolution of drowned river valleys into coastal marshes is 

 in a secondary stage in the larger estuarine systems, with sand spits 

 and barrier islands forming, 



Chesapeake Bay estuarine region: All of the Chesapeake Bay 

 system from Cape Charl-es and Cape Henry Island 



Isolation from direct oceanic effects in much of the greatly branched 

 systems, the many subsystems with major river flows, and the reduced 

 concentration of the ocean salt throughout the bay and its tributaries 

 make this a unique estuarine system. This is a drowned river valley 

 with numerous similar tributary systems in various stages of evolution. 



South Atlantic estuarine region: Cape Hatteras to Fort Lau- 

 derdale^ Fla. {about 26° north latitude) 



The generally wide Continental Shelf is brushed by the warm waters 

 of the well-defined Gulf Stream. The low-lying Coastal Plain termi- 

 nates in barrier islands and marshes in which large amounts of sedi- 

 ments are being continually deposited by moderate-sized rivers fed by 

 heavy summer rainfall. Many of the drowned river valley estuaries 

 have evolved all the way to coastal marshes. Tidal ranges are small to 

 moderate, depending on local conditions. 



Caribbean estuarine region: Fort Lauderdale to Cape Romano 



{the Florida peninsula south of 26° north latitude)^ plus 



Puerto Rico and the Virgin Islands 



High temperatures, heavy rainfall, and warm ocean currents along 



practically nonexistent continental shelves result in tropical estuarine 



environments throughout this region. Coral reefs and mangrove 



swamps are the typical coastal features of south Florida, while the 



islands are mountainous and are fringed with coral reefs and beaches. 



Tidal ranges are small. 



Gulf Coast estuarine region: Cape Romano to the Mexican 

 border 



A wide Continental Shelf extends all the way around this large 

 embayment, in which warm tropical waters are moved gently by weak 

 currents and small tidal ranges. Heavy rainfall over most of the area 

 brings sediments from the broad coastal plain to be deposited in the 

 estaurine zone. Most of the drowned river valleys have evolved to a 

 point intermediate between those of the Middle and South Atlantic 

 regions — barrier islands are extensive and have large shallow bays 

 behind them. 



The Mississippi, carrying drainage from 41 percent of the co- 

 terminous land mass of the United States, forms one of the major 



