ESTUARIES are recognized as being of critical 

 importance in man's harvest of economically 

 useful living marine resources. It is in these areas 

 that the maximum conversion of solar energy into 

 aquatic plant life takes place and they are jusdy 

 identified as "nurseries" since so many animals 

 utilize them for feeding their early life stages. Some 

 species, such as the oyster, spend their entire life 

 span in the estuary, while the shrimp and men- 

 haden reside there only as juveniles. The salmon 

 and a few others use the estuary primarily as a 

 pathway. In sum, however, more than half of the 

 over 4.5 billion pounds of fishery products har- 

 vested by U.S. fisherman annually is derived from 

 animals dependent for their existence on clean 

 estuarine waters during some part or all of their 

 life cycle. 



Pollution of estuarine and coastal waters is diffi- 

 cult to assess because of the special qualities of 

 this environment. Technically, any foreign sub- 

 stance or environmental condition that inter- 

 feres with a desired use may be considered a pol- 

 lutant, but we are concerned with those substances 

 present at high enough concentrations or en- 

 vironmental changes great enough to cause de- 

 leterious effect. Many naturally occurring sub- 

 stances in salt water become toxic when their 

 concentrations are increased artificially or by 

 natural processes. 



The problem in establishing criteria in estuaries 

 arises from the fluctuating nature of the water 

 quality, both daily and seasonally, and geograph- 

 ically within the estuary. Changes in salinity, pH, 

 turbidity, and temperature may alter greaUy the 

 critical toxic concentration of a pollutant. Most 

 chlorinated hydrocarbon pesticides, for example, 

 are significantly more acutely toxic at summer 

 rather than winter water temperatures and at least 

 one of the common detergents becomes decidedly 

 more toxic to fish as salinity levels increase. 



The most obvious effect of tidal action in the 

 estuary is to change water depth. This indirectly 

 changes current patterns, water temperature, and 

 the density of motile animal populations. Depend- 

 ing on the geography of the estuary and the 

 amount of fresh water drainage into it, salinity 

 patterns may vary from relatively uniform condi- 

 tions throughout a tidal cycle to situations in 

 which the> water is clearly stratified with a layer of 

 relatively fresh water overlying the bottom salt 

 water, or to situadons in which the major portion 

 of the water mass changes from fresh to salt and 

 back to fresh again. 



In shallow, broad estuaries, wind may be the 

 dominant factor in causing water movements 

 which change salinity and temperature patterns. 



The volume of fresh water discharged into an 

 estuary may be a major factor in establishing 

 coastal currents that transport pollution loads from 

 one region to another. 



We are dealing, then, with an environment in 

 which the characteristics of the receiving water are 

 usually fluctuating, frequently unexpectedly. As a 

 result, its ability to dilute and disperse a burden of 

 toxicants is unpredictable without detailed local 

 investigations. 



Pollution in the estuary may be derived from 

 contamination hundreds of miles upstream in the 

 river basin or it may be of purely local origin. Silt 

 plays a major role in the transport of toxicants, 

 especially pesticides, down to the estuary. Agri- 

 cultural chemicals are adsorbed on silt particles. 

 Under poor farming practices, as much as 11 tons 

 of silt per acre per year may be washed by surface 

 water into a drainage basin. Surface mining and 

 deforestation further accelerate the process of ero- 

 sion and permit the transport of terrestrial chemi- 

 cal deposits to the marine environment. 



Atmospheric drift is also an important factor in 

 the transport of pollutants to the aquatic environ- 

 ment (Cohen and Pinkerton, 1966). Much of the 

 tonnage of aerially applied pesticides fails to reach 

 the designated spray areas and the presence of 

 5 /xg/1 of DDT in presumably untreated Alaskan 

 rivers indicates the magnitude of this facet of the 

 pollution problem. The continuous presence of 

 5 /xg/1 of DDT in the marine environment would 

 decrease the growth of oyster populations by 

 nearly 50 percent. 



Toxic pollutants may be passed directly into 

 the marine environment as contaminants of in- 

 dustrial and domestic waste effluents or they may 

 be intentionally placed there as in the control of 

 various noxious insects by spraying marsh and 

 littoral habitats with synthetic pesticides. Experi- 

 mentally, some synthetic insecticides have been 

 applied direcfly to estuarine bottoms in efforts to 

 control oyster pests. 



Finally, there are naturally occurring substances 

 such as lignins and phosphate compounds which 

 in times of flood may be carried to the estuary in 

 sufficient quantity to constitute a pollution hazard. 



Salinity 



The spadal and temporal distribution of salinity 

 profoundly affects the activides of many estuarine 

 species in tidal tributaries (Andrews, 1964; Emery 

 and Stevenson, 1957; Hargis, 1965 and 1966; 

 Pearse and Gunter, 1957; Pritchard, 1953). Some 

 bottom organisms, e.g., Crassostrea virginica, are 



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