32 



present chance for a catastrophic spill of oil or other hazardous mate- 

 rials. The large volumes of petroleum and chemical products trans- 

 ported through the estuarine zone by ships, barges, pipelines, tracks, 

 and railroads present a continuing opportunity for accidental bulk 

 spills. Tlie consequences of these spills depend on the amount and type 

 of material released and the characteristics of the receiving water. 

 They may range in magnitude from tragic loss of life to little more 

 than economic loss for the transporter. 



The effect any pollutant has on an estuarine environment depends 

 on where it goes, how strong it is, and how rapidly it is assimilated or 

 flushed out of the environment. All of these conditions depend on water 

 movement and circulation patterns which are in turn governed by the 

 relationship of tide and riverflow to estuarine shape and size. Physical 

 modifiGations such as the dredging of new or deeper navigation chan- 

 nels, building of causeways or jetties, and even construction of pier 

 bridges can cause subtle changes in water movement that can change 

 the balance of environmental conditions in an estuarine system and 

 result in ^adual undesirable changes in the ecosystem in addition to 

 direct habitat damage. 



SOURCES OF POLLUTION 



Nearly all of man's activities can result in environmental degrada- 

 tion. Pollutants and polluting conditions are very rarely unique to a 

 particular use or specific activitv, but ma^ result from man's existence 

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

 lution are these : 



(1) Those sources associated with the extent of development 

 of the estuarine zone, including waste discharges from munici- 

 palities and industries, and land runoff from these as well as 

 agriculture ; 



(2) Those sources associated with particular activities of great 

 pollutional si^ificance, specifically^ dredging and filling, water- 

 craft operation, underwater mining, and heated effluent 

 discharges ; 



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

 lation and upstream water quality. 



Over 8 billion gallons of tnurdcipal 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 si^ificant 

 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- 

 charged to estuarine waters receive secondary treatment, with the 



