A relatively small amount of dredging may be necessary where these small 

 lines cross existing watercourses. The concentrations of suspended 

 nutrients and sediments are temporarily increased in localized areas near 

 the site. 



When large open-water marsh areas are encountered, it is often less 

 expensive and easier to route surface lines around such natural features 

 by using existing road and/or canal levees rather than to dredge a new 

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

 Installation causes few additional alterations of any significance to 

 such disturbed sites. Various types of simple structures may be used to 

 elevate small flowlines across open water areas. Airboats or motor boats 

 may be used for site access and to facilitate construction activities. 



Installation of a major gas/oil pipeline generates many alterations 

 similar to those associated with dredging access canals. A typical 

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

 ding 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. The plant assem- 

 blages affected depend upon the particular characteristics of 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 vegetation within the easement corridor to 

 the point that, although not destroyed, it is of little benefit to depen- 

 dent 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 considered beneficial for several reasons: (1) the 

 reproductive potential of the pest species is reduced; (2) dense, unbroken 

 stands may be opened, thereby attracting desirable wildlife species; and 

 (3) favored plant species may be encouraged to invade the disturbed sites. 



An extensive variety of consumer species is attracted by the wide diver- 

 sity and abundance of producer species and associated habitat conditions 

 so typical of freshwater wetlands. Broad generalizations regarding the 

 response of any particular consumer groups beyond the level of major 

 alterations are of little practical value, as consumer response is a 

 function o'f many complex site-specific characteristics and interactions. 

 If pipeline ditches are backfilled to near original site conditions 

 following completion of installation operations, recovery by the dominant 

 floating, submergent, emergent, or wet-meadow plant complex can immedi- 

 ately begin. Otherwise, if the channel is not backfilled, open-water 

 areas bordered by elevated spoil levees (vegetated by new plant assem- 

 blages) are substituted for highly productive fresh marsh. New aquatic 

 consumer groups, i.e. aquatic invertebrates, fish, alligator, and some 

 wading birds may respond to newly created open-water habitats. The 



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