and raptors) might be adversely affected if the alteration were 

 extensive enough. The magnitude of alterations described above 

 varies according to channel dimensions, number of channels, channel 

 orientation relative to freshwater and saltwater sources, levee 

 orientation and placement, the hydrologic gradient of the watershed, 

 and other site-specific characteristics. 



Channel excavation increases total suspended sediments. Secondary 

 effects in vegetated areas are typically temporary and localized in 

 areal extent. In open-water sites, increased suspended sediments 

 temporarily increase water turbidity and sedimentation rates, as 

 well as local biological oxygen demands (as the result of high soil 

 organic content). Sediment dispersion, however, may affect more 

 extensive areas, depending upon prevailing water velocities and 

 circulation patterns. Increased water turbidity can briefly inhibit 

 phytoplankton productivity. Increased biological oxygen demand may 

 temporarily deplete dissolved oxygen levels, thus stressing nearby 

 fish and aquatic invertebrate populations. Barren spoil banks or 

 levees contribute to prolonged increases in the amount of suspended 

 sediments as a result of surface erosion and runoff. Establishment 

 of plant ground cover moderates such erosion. 



Disturbances associated with channel construction or line installa- 

 tion typically cause short-term displacement of sensitive wildlife 

 species from otherwise favorable nearby habitats. Displacement may 

 affect feeding waterfowl concentrations and bird rookeries. Depend- 

 ing upon the sort of line or pipeline installation method (back- 

 filled or open canal), vertebrate movement patterns may undergo 

 short- or long-term alteration. Following activity completion, 

 species reenter nearby sites if the areas remain essentially 

 unaltered. However, human activity and associated noises during 

 construction extend project effects beyond the boundaries of the 

 immediate site. 



Key attribute alterations 



Alterations associated with line installation are functions of line 

 size, site location, and placement methodology. Surface flowlines 

 and supply lines and permanent overhead lines within road and access 

 canal easements typically generate short-term impacts of limited 

 areal extent that are quickly reclaimed by the system and generate 

 little, if any, noticeable subsequent effects on consumer compo- 

 nent's. Gas and oil transportation pipelines, on the other hand, can 

 modify important ecosystem attributes. Key alterations involve: 

 (1) changes in land elevations, either through canal dredging and/or 

 spoil deposition, both of which may lead to fundamental alterations 

 of the existing marsh hydrological regime, and (2) direct removal of 

 productive brackish marsh vegetation and dependent consumer groups 

 as a result of dredging and spoiling activities. Resulting produc- 

 tivity losses may be either temporary or long term depending upon 

 the installation technique used and the extent of site restoration. 



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