Box 1.1 The Coastal Zone

The 19 coastal states of the coterminous United States include about 8,000 kilometers (5,000 miles) of coastline along the Gulf of Mexico, the Pacific Ocean, and the Atlantic Ocean. Adding Alaska, Hawaii, and island territories, the United States has a total of 20,600 kilometers (12,400 miles) of coastline.

The United States has an Exclusive Economic Zone (EEZ) jurisdiction to a distance of 200 miles (333 kilometers) offshore of the coastline, an area of approximately one million square miles (2.65 million square kilometers). This is about half again as large as the land area of the contiguous United States. The EEZ area contains about 125,000 cubic kilometers of sea water, an amount about 180 times the volume of all inland estuaries and providing a comparable larger dilution capacity for waste.

Despite the dilution capacity of coastal waters, there are large variations in the characteristics of the United States' coastal zone that warrant caution in marine waste disposal. Divisions of the coastal zone that are of concern in wastewater management include: 1) estuaries (i.e., inland extensions of the ocean, progressively diluted by fresh water); 2) open coastal waters overlying the continental shelf; and 3) ocean waters themselves, overlying the deepening slopes, submarine basins, and canyons beyond the coastal continental shelf. Much of the Pacific coastline is straight with deep waters that have open shelf or oceanic characteristics. In contrast, most of the Atlantic and Gulf shoreline of the United States is indented with hundreds of shallow estuaries along which much of the population lives and works. These estuaries connect inland freshwater systems to the ocean. Indeed, there is no dividing line in the estuarine environment between the fluvial and marine world; gradations between sea and river are subtle, occurring sometimes over hundreds of kilometers as a function of river flow, tidal flow, channel gradient, and oceanic conditions. Because estuaries are shallower and more confined than the open coastline, these environments are less able to accept and disperse effluents. In addition, the circulation associated with estuaries often leads to the trapping of particles in the region where the fresh and saline waters meet. This trapping region is a potential site for the accumulation of toxic compounds.

Estuaries provide critical habitat for much of the productivity and diversity of marine fish, shellfish and coastal wildlife of the United States. Most of the major fisheries of the United States (finfish, oysters, clams, shrimp) are based on species that are highly dependent on estuarine habitats for reproduction and growth. Critical habitats include intertidal and subtidal mudflats; thousands of acres of submerged aquatic vegetation and dense salt marshes, which provide refuge for fish, crabs, and shrimp and for complex food chains that lead to large fish; and great populations of shore birds, ducks, geese, and numerous mammals, reptiles, and amphibians. These are the ecosystems in most need of protection from coastal development and pollution.

Continental shelf waters, which often are chemically, physically, and biologically distinct from the adjoining ocean, extend between the coast or



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement