269 



sewage because of the oil and other materials carried from the streets 

 andyards(fiff.IV.5.18). 



Figure I vTl.lS shows the seasonal variation in precipitation for 

 selected coastal stations. This figure shows a rather varied distribution 

 of precipitation throughout the national coastal areas and indicates the 

 seasons when runoff could present problems. 



In addition to the pollutants carried in the runoff, the fresh water 

 itself may stress the ecosystem through dilution of the salinitv to con- 

 centrations lower than those necessary to support some life forms. A 

 case in point is the annual killing of aquatic vegetation in Tampa Bay 

 with the onset of summer rains (fig. IV.5.19) . 



Last in runoff consideration is the degree of flow regulation or water 

 resource development upstream from the tidal environment. These 

 upstream impoundments, with the attendant flow regulation, may have 

 both beneficial and detrimental effects. The reservoirs can serve as 

 equalizing basins, providing a rather constant quality of estuarine 

 fresh water inflow. The difference between regulated flows and nat- 

 ural flows however, may cause ecological stress through alteration of 

 the salinity regime or the circulation patterns. Table IY.2.11 is a com- 

 pilation of flow regulation structures on major estuarine streams. 



Section 3. Extent of Pollution Effects 



Environmental damage from human activities manifests itself in 

 changes in water quality and in changes in living communities. Either 

 or both may be caused by any of the kinds of pollution or sources of 

 pollution already discussed. 



This section contains separate discussions of degradation of water 

 quality and damage to living communities, but water quality is an 

 integral part of estuarine ecosystems and changes in one are usually 

 reflected in the other. An accurate and thorough analysis of the re- 

 lationship of pollution to environmental damage must recognize these 

 related factors. The compartmentation of discussion in this section is 

 necessary because water quality studies and ecological studies are 

 rarely conducted simultaneously in the same system. This situation, 

 indeed, is one major existing deficiency in the present approach toward 

 study of the estuarine environment. 



degradation of water QUALII*r 



One key to the degree of environmental impact is measurement of 

 alteration in water quality. Extensive data have been collected on a 

 few of the estuaries with the most severe problems, and limited in- 

 formation is available on other estuarine systems to outline the emer- 

 gence, or document the existence, of water quality problems. For the 

 majority of the Nation's estuarine systems, however, there are little 

 or no data to describe existing water quality conditions. 



The northeastern coast of the United States is the most intensively 

 used and the best studied part of the estuarine resource (fig. IV.5.21) . 

 From the Virginia-North Carolina border to the tip of Maine there are 

 10 Coastal States encompassing 15 major estuarine systems and har- 

 boring an estimated 1966 population of 45,416,000. Economic develop- 

 ment includes a wide variety of commercial, industrial, and 

 governmental activities. Nearly all waste products from this all- 



