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in the estuarine zone as well as his use of it. The major sources of 

 pollution : 



(1) Those sources associated with the extent of development of the 

 estuarine zone, including waste discharges from municipalities and 

 industries, and land runoff from these as well as agriculture ; 



(2) Those sources associated with particular activities of great 

 pollutional significance, specifically dredging and filling, watercraft 

 operation, underwater mining, and heated effluent discharges; 



(3) External sources having impact derived through flow regula- 

 tion and upstream water quality. 



Over 8 billion gallons of municipal wastes are discharged daily into 

 the waters of the estuarine zone. While most of this volume is domestic 

 sewage, many municipal waste discharges also contain significant 

 amounts of industrial wastes, which may add to the variability and 

 complexity of the wastes discharged. Municipal waste discharges have 

 four important effects on receiving water quality: depletion of dis- 

 solved oxygen, and introduction of pathogenic organisms, settleable 

 material, and inorganic nutrients. 



Sewage treatment reduces and alters the impact of municipal waste 

 on the environment. Primary treatment with chlorination will remove 

 part of the decomposable organic material, nearly all of the settleable 

 and suspended solids, and almost eliminate the possibility of pathogens 

 in the effluent. Secondary treatment can almost eliminate decompos- 

 able organic material, and some special processes can eliminate certain 

 kinds of dissolved salts. About one half the municipal wastes dis- 

 charges to estuarine waters receive secondary treatment, with the most 

 extensive use of secondary treatment being in the Chesapeake Bay 

 estuarine region. 



Associated with the major metropolitan developments are large num- 

 bers of industrial complexes with their attendant waste products. 

 Many of these industrial wastes ^ especially from the chemical industry, 

 are of such a complicated nature that it is difficult both to identify them 

 and to assess their effects on the receiving streams. Only 4,000 of the 

 more than 200,000 manufacturing plants in the coastal States account 

 for 97 percent of the total liquid wastes discharged. Of the nearly 22 

 billion gallons of industrial wastes discharge daily, only 29 percent 

 receive any kind of waste treatment. 



Intensification of use of the estuarine zone has resulted in many 

 artificial changes being made in the physical structure. Shoreline areas 

 have been filled to create more land area for residential and commercial 

 use ; channels have been dredged and maintained to permit safer and 

 better navigation ; and harbor facilities have been dredged and bridges 

 and causeways have been built. All of this activity has had impact on 

 the coastal zone ecosystem, but the activities having the most impact 

 on water quality are dredging and filling. The potential for pollution 

 of the system exists in both filling and dredging; both can introduce 

 foreign materials into the water, destroy aquatic habitat, and physical 

 circulation patterns. 



The primary source of thermal pollution is from industrial cooling 

 water effluents. Powerplants are the major users of cooling water in the 

 estuarine zone, and power-generation capacity has approximately 

 doubled each decade du'ring this century. The impact of this growth 

 on the estuarine areas is evidenced by the fact that in 1950 22 percent 



