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 

 depending upon the size of the line, which therefore results in 

 direct habitat alterations ranging from 1 to 10 ha per km (3.6 to 

 36 acres per mi) of easement. Dredging and spoil deposition 

 directly remove the marsh vegetation Spartina patens and Scirpus 

 spp. within portions of the easement. Heavy marsh buggies crush and 

 trample other nearby vegetated areas. Food and cover resources for 

 consumer groups are removed directly with loss of food-bearing and 

 cover-producing plants. Consumers such as the various waterfowl 

 species, furbearers, small mammals, terrestrial insects, aquatic 

 invertebrates, alligator, and some wading and/or shorebirds are 

 affected. If pipeline ditches are backfilled upon completion of 

 installation procedures, recovery of Spartina can immediately begin; 

 otherwise, if the channel is not backfilled, open-water channels, 

 bordered by elevated spoil levees and vegetated by new plant assem- 

 blages, are substituted for highly productive brackish marsh. 

 Phytoplankton (plant assemblage 14) may increase in the deeper water 

 bodies (Corliss and Trent, 1971). However, the total net production 

 of organic material decreases in altered areas compared to the 

 original marsh (Darnell, 1976). 



There may be decreases or increases in numbers of consumers in 

 pipeline canals (Bourn and Cottam, 1950; Willingham et al., 1975; 

 Adkins and Bowman, 1976). Measures of total biomass have often 

 shown decreases (Trent et al., 1972), though measurements have not 

 been consistent in all canals. Relative shifts in species abundance 

 are evident with creation of deeper water bodies (Lindall et al., 

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



It is difficult to predict which groups of consumers increase or 

 decrease because many species use organic material from a variety of 

 sources for food. The kinds and numbers of organisms existing in 

 the isolated, sometimes nonflowing, water bodies depends upon fre- 

 quency, timing, and amount of tidal inundation. Willingham et al. 

 (1975) and Adkins and Bowman (1976) compared abundance of various 

 consumers in control, open, semiclosed, and closed pipeline canals. 

 Overall, control areas and open canals were better habitats for 

 estuarine species as evidenced by diversity and abundance measure- 

 ments. However, semiclosed and closed canals generally contained 

 the largest organisms and were favored by many arthropods, particu- 

 larly shrimp. 



Other organisms, particularly predators further along the food chain 

 may increase or decrease depending upon the amount of area affected 

 and the types and quantity of consumer species available as food. 

 However it is usually the case that areal increases in standing-water 

 habitat do not compensate for the losses of marsh resulting from the 

 construction activity. 



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