575 



face are complementary in many ways. The alteration of either one is 

 reflected in the change in effect of the other. In some cases the estuary 

 is a gradual continuum from fresh to sea water ; in others the lines of 

 demarcation are abrupt and well defined. The most obvious physical 

 demarcations of land drainage-estuary-sea are based on salinity, thus, 

 the discussion of these two interfaces is combined. 



It is established that various biological life is dependent on salinity 

 gradients throughout the estuarine zone. For example, the high value 

 of the Gulf coast shrimp industry is dependent on the bays as nursery 

 grounds; however, the amounts and quality of fresh water required 

 to support the ecological system of each individual bay has not yet 

 been established. Tliis is a pressing research need. 



Fresh water inflows of many of our bays have already been reduced 

 or altered through construction of upstream water supply dams. In 

 addition to the obvious effect of increasing salt water intrusion into 

 fresh water systems of the riverine flows, we must also know how the 

 estuarine habitat is being limited by this increased salinity due to 

 increased ocean influence and the reduced mass of water in a more 

 brackish condition. The same question might well be framed with any 

 of the many other forms of parameter alteration that have occurred. 

 Temperature increase in critical areas might be extremely important, 

 perhaps far in excess of the actual amount of water being affected, for 

 if a critical area is affected, we might find ourselves with a situation 

 of a "gate" that has been closed and whole areas of a formerly 

 beneficial ecosystem removed from use by desirable organisms. 



Residual pollutants 



Eesidual poUutional material such as trace organic compounds and 

 minerals, pesticides, herbicides, heavy metals, etc., are reaching 

 estuarine areas from either surface runoff or riverine inputs. The spe- 

 cific kinds, amounts, and effects of these compounds are generally 

 unknown. Investigations are needed to identify and quantify the resid- 

 ual pollutants and to evaluate their poUutional effect. These investi- 

 gations should include, but not be restricted to, shellfish, tissue 

 buildup of residuals, tainted fish flesh, destruction of food chains, and 

 intrusion into other standing compartments of the estuarine ecosystem 

 such as the sediments, the marsh, or the major rooted aquatic plants 

 therein. 



Contiguous wetlands 



There also needs to be a thorough study of the relationship of con- 

 tiguous wetland to estuarine ecological systems, including the effects of 

 drainage on estuarine water quality. The salt marshes which are ir- 

 regularly flooded are especially important. These are areas which are 

 flooded by tide only at sporadic intervals, and consequently, there is 

 no regular interchange of water with the estuary. It has generally 

 been assumed, and what scanty data are available support the assump- 

 tion, that such marshes contribute very little to the estuary in the way 

 of organic matter and nutrients. The case for the importance of regu- 

 larly flooded marshes has been made convincingly and consequently 

 there is general agreement on the importance of their preservation. 



People tend to regard the irregularly flooded marsh as expendable, 

 and the pressures for modification of this habitat rapidly are becoming 



