IV-371 



The direct damage is not the total economic impact. The cost of 

 cleanup must be added and is considerable. The ever-present threat 

 of a catastrophic spill places the estuarine treasure house of resour- 

 ces in jeopardy. 



DELIBERATE PHYSICAL MODIFICATION 



Building a bridge, dredging a channel, and filling land for a housing 

 development are not ordinarily regarded as forms of pollution, yet 

 they can cause damage to the biophysical environment far more 

 devastating than the most potent industrial or municipal waste. 



Physical modification is permanent; once an estuarine habitat is 

 destroyed by dredging or filling, it is gone forever. No waste 

 treatment can correct or even minimize the damage. The destruction 

 of a marsh or part of the estuarine shallows has an obvious effect 

 on habitat value, but equally severe damages can be associated with 

 apparently minor physical alterations. 



The effect any pollutant has on an estuarine environment depends on 

 where it goes, how strong it is, and how rapidly it is assimilated or 

 flushed out of the environment. These conditions depend on water 

 movement and circulation patterns, which are in turn governed by the 

 relationship of tide and river flow to estuarine shape and size. 

 Dredging of new or deeper navigation channels, building of causeways 

 or jetties, and even construction of bridge piers can cause subtle 

 changes in water movement that can alter the balance of environmental 



