levees. Lines are usually laid directly on the levee shoulder or toe. 

 Installation causes few additional alterations to such disturbed sites, 



Installation of a major gas/oil pipeline generates many alterations 

 similar to those associated with dredging an access canal. A typical 

 pipeline easement ranges from 10 to 100 m (30 to 300 ft) in width 

 depending upon line size and installation methodology. Direct habitat 

 alterations, therefore, range from 1 to 10 ha per km (3.6 to 36 acres per 

 mi) of easement. Dredging and spoil deposition directly remove all types 

 of marsh vegetation within portions of the easement. Which plant assem- 

 blages are affected depends upon the characteristics of and location 

 within the specific marsh. 



Food and cover resources for consumer groups are removed directly with 

 loss of food-bearing and cover-producing plants. Heavy marsh buggies or 

 draglines crush and trample other vegetation within the easement corridor 

 so that it is of little benefit to dependent consumer groups. Fresh- 

 meadow plants, emergents, and shallow-water submergents would be most 

 directly affected. In some cases where the existing flora consists 

 primarily of noxious pest species, vegetation alterations may be con- 

 sidered beneficial for several reasons: (1) the reproductive potential 

 of the pest species is reduced; (2) dense, unbroken stands may be opened 

 up, thereby attracting desirable wildlife species, and (3) favored plant 

 species may be encouraged to invade the disturbed sites. In this 

 instance, an extensive variety of consumer species may be attracted by 

 the new diversity and abundance of producer species and associated 

 habitat conditions. 



If pipeline ditches are backfilled to near original site conditions after 

 pipe placement, recovery by the dominant floating, submergent, emergent, 

 or wet-meadow plant complex can immediately begin. If the channel is not 

 backfilled, however, open water bordered by elevated spoil levees that 

 are vegetated by new plant assemblages is substituted for highly produc- 

 tive fresh marsh. New aquatic consumer groups, such as aquatic 

 invertebrates, fish, alligator, and some wading birds may respond to 

 newly created open-water habitats. However, the areal increase of these 

 open-water areas is usually less than the areal decrease resulting from 

 construction activities. 



Marsh buggies, draglines, and other equipment associated with canal 

 excavation depress the marsh surface, forming numerous ruts and other 

 depression?. Such depressions nay alter existing water flows by 

 channeling surface waters in new directions. Such alterations could 

 affect large areas if critical drainages are affected; usually, however, 

 affects are quite localized in the fresh marsh. Small open-water bodies 

 or elevated mounds may be created, but such changes normally are of minor 

 consequence at the ecosystem level. Heavy traffic concentrated along one 

 route, however, may produce ruts capable of channeling surface waters 

 such that freshwater runoff into and/or out of the marsh is altered. 

 Intramarsh circulation could be affected as separate water bodies are 



255 



