574 



between thermal effects and effects of the saline wedge (resulting from 

 a long term natural fluctuation) on the river animals in many in- 

 stances. In this case, a history of intensive physical observations, cor- 

 related with occasional biological surveys accumulated over an ex- 

 tended period of time (such as has been extensively discussed earlier 

 in connection with baseline studies) , may well have resulted in a basis 

 for separating the natural from the manmade 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 buildup of temperature 

 and salinity. While the fauna of these areas has adapted to the natural 

 buildups, the discharge of heated waters and reduction of freshwater 

 inflows may result in buildups to a level above that of any natural 

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

 effects of proposed thermal and high dissolved residue content waste 

 discharges, investigations into the temperature and salinity charac- 

 teristics of each estuarine area are needed. Correlated with this is the 

 need to understand the biological principles of estuarine management. 



Timing of natural variation 



For the most part, we know that brackish water is necessary for the 

 maintenance of a large fraction of our coastal fisheries. We do not, 

 however, know exactly what are the limits of salt concentration that 

 will encourage optimal development of desirable species. In addition 

 to this, we have little idea of the optimal seasonality of salinity 

 changes. Although it is apparent that a seasonal fluctation of salinity 

 may be desirable, we scarcely have an idea as to when it would be best 

 to reduce or raise the salinity. We do know when certain important 

 food animals reproduce, so we might assume that reduced salinity 

 would be most optimal at this time, but we do not know what would 

 be the effects of raised salinities in other seasons. All work of this kind 

 on natural variations ties back to the baseline studies proposed earlier 

 in this report. 



INTERFACE FACTORS 



An important portion of understanding the ecology of the estuarine 

 system is a knowledge of interface factors. By this we mean the ex- 

 changes which occur between the estuarine waters and offshore waters, 

 the influx of fresh water and other drainage from the land ; between 

 the water mass and the bottom sediments ; and between the water mass 

 and the atmosphere. Another area of interface concern, the movement 

 of materials between the biological compartment and the aquatic com- 

 partments of the estuary, is the major theme of much of this chapter 

 and hence will not be discussed here. 



Land drainage — estuary — sea interface 



Because the estuary itself is the interface between the sea and the 

 land, the ocean-estuary interface and the estuary-land drainage inter- 



