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studies. A long term drought has resulted in an intrusion of 

 a saline wedge into the upper reaches of the river. A power 

 plant has been introducing thermal effluents into the river. 

 It has been impossible to distinguish between thermal effects 

 and effects of the saline wedge (resulting from a long term 

 natural fluctuation) on the river animals in many instances. 

 In this case, a history of intensive physical observations, 

 correlated with occasional biological surveys accumulated over 

 an extended period of time (such as has been extensively dis- 

 cussed earlier in connection with baseline studies), may well 

 have resulted in a basis for separating the natural from the 

 man-made alterations in animal populations. These observations 

 need not have been carried out on the Patuxent River itself, 

 but rather need only to have been concerned with the detailed 

 documentation of saline encroachment into a brackish system. 

 Another example of the importance of knowing natural variations 

 occurs in the bays along Texas, Louisiana, and other areas of 

 the Gulf Coast. In general, these bays are shallow bodies of 

 water with large surface areas. They are thus subject to natural 

 build-up of temperature and salinity. While the fauna of these 

 areas has adapted to the natural build-ups, the discharge of 

 heated waters and reduction of freshwater inflows may result 

 in build-ups to a level above that of any natural condition. 

 In order to provide a firm basis for the evaluation of the 



