286 



changes in sedimentation patterns and an apparent decrease in produc- 

 tivity in some areas (IV-6-4) . 



Mining 



The taking of materials from the estuarine bottom immediately de- 

 stroy the local habitat and the movement and settling of suspended 

 material may extend the damage to other areas. Sand and gravel 

 dredging are universal activities in the estuarine zone; oyster shell 

 dredging exists in several areas along the Gulf and Atlantic coasts. 



Posphate sand or rock mining in estuarine systems may raise the 

 concentration of phosphorus in the water and change the ecological 

 balance of the entire estuarine environment, as well as directly killing 

 fish and other aquatic organisms. 



Mining operations exploit a nonrenewable resource, and even after 

 mining operations have ceased, the hole in the bottom of the estuary 

 may affect water circulation throughout the estuarine system. 



Flow regulation 



The ecological balance of an estuarine system is the result of inter- 

 action of the dominating environmental factors discussed in part IV, 

 chapter 1. Among these factors are the amount and annual distribution 

 of fresh water inflow. Upstream flow regulation may have many 

 beneficial effects, but radical changes in the annual riverflow pattern 

 may cause drastic changes in both water circulation and in ecological 

 balance. 



The harbor of Charleston, S,C. was a deepwater port with fresh- 

 water inflow from only coastal drainage until the flow of the Santee 

 River, averaging 15,000 cubic feet per second, was diverted into it. 

 This caused salinity stratification to set in and sedimentation became 

 a severe problem. Dredging requirements grew from 120,000 cubic 

 yards per year to over 7,000,000 cubic yards per year and many of 

 the docks had to be abandoned because adequate depths could not be 

 maintained. The prohibitive dredging costs have resulted in a Corps of 

 Engineers proposal to redivert the Santee River away from Charleston 

 Harbor (see case study p. 302) . 



Some of the more productive oystering areas in the Potomac River 

 are in a reach where high springtime river flows reduce salinities 

 enough to kill the oyster drills (a predator) but not kill the oysters. 

 Flow regulation to reduce the high spring flows would probably change 

 this relationship. 



RESTRICTIVE IMPACTS 



Some estuarine uses may restrict use for other purposes but do not 

 automatically exclude other uses. These are those activities which do 

 not require a permanent modification of the estuarine system; they 

 generally include those uses directly involved with the estuarine 

 waters and other renewable resources. 



Restrictive impacts may involve damage to water quality, living 

 organisms, or aesthetic quality ; such impacts may also result from the 

 exclusive appropriation of space. The key feature of uses which cause 

 restrictive impacts is that they may, with proper management, be car- 

 ried out simultaneously with other uses. 



