abundance are evident along with changes in absolute numbers as the 

 area is altered in character from marsh to a deeper water body 

 (Lindall et al., 1973; Dale, 1975; Adkins and Bowman, 1976). 



With a shift in primary producer type, consumers dependent upon 

 phytoplankton may increase in the affected area. Those dependent 

 upon epiphytes and marsh grasses will decline. Consumers further 

 along the food chain such as wading birds may increase or decrease 

 depending upon disturbance factors and the sorts of consumer species 

 available for food. 



Disturbance factors should be recognized as an important considera- 

 tion because they extend the effects of the project beyond the 

 boundaries of the immediate site. 



4. Key attribute alterations 



Key attribute alterations induced by this phase of oil and gas 

 operations involve changes in land elevations. Canals increase the 

 frequency and area of inundation by salt water. They may increase 

 the volume of water exchange, accelerate freshwater runoff, and 

 hasten the drying of high marsh areas. In dead-end canals far 

 removed from tidal influence, anoxic conditions may develop. Depend- 

 ing upon spoil bank configuration, tidally flushed salt marsh may 

 become impounded and may change character considerably. 



First-order effects include removal of vegetation and creation of a 

 standing water habitat. If the saltwater flows are not confined by 

 spoil and/or natural topographic features, much larger areas of 

 marsh may be affected. Long-term changes in vegetation and consumer 

 groups would occur. Long-term turbidity increases would also result. 



Canal construction requires spoil placement. In salt marshes this 

 usually results in higher land elevations. Burial of flora may be 

 an immediate alteration. Even more significant, however, may be the 

 possible alterations of waterflow regimes. Poorly planned placement 

 of spoil may result in blockage of existing tidal inundation and/or 

 runoff patterns. These blockages will lead to long-standing changes 

 in types and/or amounts of vegetative cover, followed by appropriate 

 changes in consumers. 



Wellsite preparation and operation for leveed marsh-floor locations. 

 1. Activity sequence 



The equipment and techniques utilized during construction of the 

 access road are also employed during preparation of the wellsite. 



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