100 



plus the tidal flow. Such estuarine systems purge themselves very 

 rapidly of waste discharges. 



With wider channels, smaller river flows, and greater tidal ranges 

 more mixing occurs and other forces come into play. Enibayment 

 shape, bottom configuration and material, and the effects of the earth's 

 rotation all may play a role. In some estuarine systems of this type, 

 the degree of stratification may change with changes in river flow, 

 temperature, wind, or other transient conditions. 



The James River is a drowned river valley in the Chesapeake Bay 

 estuarine region (fig. IV.1.27). Its length of tidal influence is 

 great in proportion to its width, and it exhibits some vertical stratifi- 

 cation. Delaware Bay is much wider than the James and is stratified 

 laterally (fig. IV. 1.28) ; that is, salt content along the eastern shore 

 tends to be higher than that along the western shore. This phenomenon 

 probably results from forces, associated with the earth's rotation, 

 which in large bodies of water tend to cause lateral stratification as 

 a result of the different rates of slipping of salt and fresh water on the 

 spinning earth's surface. 



Hillsborough Bay, an arm of Tampa Bay, is nearly unstratified and 

 quite salty during much of the year. During high flows, however, the 

 Hillsborough River pushes the salt out of the upper part of the bay 

 and often kills heavy growths of a salt water plant which is not toler- 

 ant of fresh water. 



Some very large embayments with small ocean entrances such as 

 Pamilco Sound have very small tidal ranges, very little stratification, 

 and throughout most of their area, very weak currents (fig. IV. 1.4) . 

 Only at the channels to the ocean are currents strong, and there they 

 are often extremely violent and dangerous. Wastes discharged into 

 such embayments tend to remain for long periods and exert their 

 effects in the estuary rather than moving out to sea. 



NATURAL WATER QTJALrrY IN THE ESTUARINE ZONE 



Estuarine water quality is the product of both land and water. From 

 the land, erosion and solution in river water bring suspended and dis- 

 solved minerals, while decaying vegetation adds dissolved organic 

 material. Sea water itself contains three percent dissolved salts, but 

 negligible quantities of organic matter. 



In the estuarine zone these two different solutions meet and mix. Salt 

 concentrations range from that of the oceans to the almost unmeasur- 

 able amounts present in some ri^'ers. Where little stratification exists, 

 sea salt dominates mineral concentrations in estuarine waters; in strati- 

 fied systems, however, the small amounts of minerals entering in the 

 fresh water may be as important in some parts of the estuarine zone as 

 tJie mudh larger concentrations from the sea are in others. The inter- 

 face between fresh and salt water is a region of complex chemistry 

 where some material may be precipitated out or otherwise changed, 

 much as lye soap used to be "salted out" when soap was made by boil- 

 ing lard with wood ash extract in the backyard. Organic matter from 

 decaying vegetation is particularly susceptible to this type of chemical 

 effect. 



Climate also plays a direct rtJle in determining estuarine waiter qual- 

 ity. Excessive evaporation can drive salinities far above those of ocean 



