standing-water habitat for phytoplankton, aquatic invertebrates, and 

 vertebrates. Such increases could prove beneficial for some consurrers 

 having habitat requirements for open water, especially if little standing 

 water was available originally. However, if the canal construction 

 results in significantly less vegetation, particularly in an area greater 

 than the construction site alone, effects on consumers may be quite 

 negative. The areal increase of favorable habitat is usually less than 

 the areal decrease resulting from indirect effects of canal construction 

 plus marsh vehicle traffic. Turbidity that results from chronic erosion 

 decreases the suitability of the standing water as habitat for phyto- 

 plankton, aquatic vertebrates, and aquatic invertebrates. 



The above discussion is oriented toward phenomena in a natural coastal 

 fresh marsh. Impoundments which create artifical fresh marshes involve 

 special circumstances that are dependent upon specific management 

 techniques. The discussion concerning effects arising from decreases in 

 land elevation may not be applicable. However, effects of blocked water 

 flows and turbidity increases may be especially pertinent. 



Wildlife displacement resulting from these construction activities is 

 difficult to predict. However, displacement is short term, as construc- 

 tion proceeds at rates up to 300 m per day. While noise and human 

 presence extend the effects of project construction beyond the boundaries 

 of the immediate site, the disturbance may be less than the effects of 

 daily boat traffic over a period of years during drilling and production 

 phases. 



Key attribute alterations 



Key attribute alterations induced by this phase of oil and gas operations 

 involve changes in land elevations. First-order effects include removal 

 of vegetation and creation of a standing-water habitat. If the new water 

 body is not confined by spoil and/or natural topographic features, much 

 wider areas of marsh may be affected by occasional saltwater intrusion or 

 deeper average water depth. Long-term changes in vegetation and consumer 

 groups could occur. Long-term turbidity increases may also result. 



Canal construction requires spoil placement; this results in higher land 

 elevations. Burial of flora is less significant than possible altera- 

 tions of waterflow regimes. Poorly planned placement of spoil may result 

 in blockage of existing upland drainage and/or runoff patterns. These 

 blockages will lead to long-standing changes in types and/or amounts of 

 vegetative cover, followed by corresponding changes in consumers. 



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