Ch. 6— Impacts and Mitigation » 119 



DEVELOPMENT ACTIVITIES 



Dredging and Excavation 



Both dredging and excavation in wetlands in- 

 volve the direct removal of wetland vegetation and 

 the underlying wetland soil. Because the elevation 

 of the dredged area is reduced, it normally will be 

 flooded by deeper water most of the time, thereby 

 eliminating the possibility of recolonization by 

 wedand plants unless the area becomes subsequent- 

 ly filled, either naturally or by man. For example, 

 dredging or excavation are responsible for wetland 

 losses associated with agricultural conversion in 

 Nebraska; mosquito-control ditching along the east 

 coast in North Carolina; canal construction in 

 coastal Louisiana, Mississippi, and Texas; peat 

 mining in Maryland, Michigan, and Minnesota; 

 phosphate mining in North Carolina and Florida; 



the extraction of other materials such as borax, 

 potash, soda ash, lithium, gold, sand, and gravel; 

 and port and other water-dependent coastal devel- 

 opment. 



Dredging commonly is used to deepen or 

 straighten waterways for navigation, port, and 

 marina facilities or for flood control. In addition 

 to the direct effects of removing wetland vegeta- 

 tion and soil, dredging may impact wetlands even 

 if it takes place offsite. Giese and Mello (21), for 

 instance, found that dredging a navigation inlet into 

 a small estuary increased the tidal range in the up- 

 per estuauy, exposing the bottom at low tide. Salini- 

 ty was increased, shellfish beds were exposed, ben- 

 thic (i.e., bottom-dwelling) invertebrate populations 

 were eliminated, and vegetation patterns were 

 changed. The dredging of canals primarily for ac- 



Photo credit: Office of Tectinology Assessment. Joan Harn 



The dredging of canals for navigation and for access to oil and gas development sites in coastal Louisiana has led to 

 saltwater intrusion into freshwater marshes. The excess salinity eventually kills the marsh vegetation 



