Chapter 5 

 The Estuarine 

 System 



Authors: Peter Larsen, Lee Doggett, Chris Garside, Jerry Topinka, Tim Mague, Toby 

 Garfield, Ray Gerber, Stewart Fefer, Patricia Shettig, Lawrence Thornton 



Estuaries are the major link between the sea and fresh water and terrestrial 

 environments. Cities and towns historically have been built on estuaries, 

 consequently, estuaries have been used as major transportation corridors and 

 waste disposal systems. Estuaries also receive the flow of rivers, which is 

 comprised of runoff from the landmass and includes pollutants from upstream 

 developments. They are used as finfish spawning and nursery grounds, 

 shellfish habitats, migratory bird feeding and breeding areas, and 

 recreational areas. This chapter examines the basic concepts and information 

 on the functions of the complex estuarine system of coastal Maine. 



The U.S. Fish and Wildlife Service (FWS ; Cowardin et al. 1979) defines the 

 estuarine system as "deepwater tidal habitats and adjacent wetlands which are 

 usually semi-enclosed by land but have open, partially obstructed, or sporadic 

 access to the open ocean and in which ocean water is at least occasionally 

 diluted by freshwater runoff from the land." Furthermore, "estuaries extend 

 upstream and landward to the place where ocean-derived salts measure <0.5 ppt 

 during the period of annual low flow. The seaward limit of the estuarine 

 system is: 1) a line closing the mouth of a river, bay or sound; 2) a line 

 enclosing an offshore area of diluted sea water with typical estuarine flora 

 and fauna; or 3) the seaward limit of wetland emergents, shrubs or trees where 

 these plants grow seaward of the line closing the mouth of a river, bay or 

 sound." Since estuaries most often are semienclosed by land they are somewhat 

 protected from marine influence and are a low-energy environment compared to 

 the marine system. Tides and riverine inputs are the dominant physical 

 factors within estuaries, although currents and wind also may be important 

 (Cowardin et al. 1979). 



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