The movement of the dragline over the marsh also crushes some vegetation, 

 although the use of wooden mats minimizes uprooting of vegetation. 



Suspended sediment and nutrient increases that accompany the excavation 

 are of short duration. The erosion of levee banks will lead to long-term 

 turbidity increases; the degree and extent of these phenomena are site 

 specific. 



The ditch created by the borrowing of fill remains for a long time. Its 

 presence diverts some upland drainage from its normal path over the marsh 

 surface; also, the adjacent areas drain more rapidly. Both of these 

 phenomena tend to make adjacent marsh regions drier than normal. The 

 average depth of standing water on the marsh decreases, while the fre- 

 quency of submergence/emergence of plants increases. 



The decrease in duration of submergence and possible increase in turbi- 

 dity can result in a decrease in production of phytoplankton on the narsh. 

 This decrease in production along with the decreased duration of standing 

 water will decrease the food for aquatic invertebrates and vertebrates. 

 These changes decrease the suitability of the area as habitat for species 

 such as alligator, waterfowl, and wading birds that prefer wetter condi- 

 tions. 



The increase in water depth in the borrow channel, however, may provide 

 favorable conditions for phytoplankton and suitable habitat for the con- 

 sumers mentioned above. In general, though, the areal increase in 

 favorable habitat will be smaller than the aeral decrease resulting from 

 the indirect effects of levee building. 



The decrease in duration of standing water and increase in frequency of 

 emergence will allow better gaseous exchange between the atmosphere and 

 the soil. This may give a slight competitive advantage to meadow-type 

 vegetation over emergents; however, no significant changes in fauna would 

 be expected because both plant assemblages support the same consumer 

 groups. Effects on other consumers are thus minor. 



The above discussion is oriented toward phenomena in a natural coastal 

 fresh marsh. Impoundments which create artificial fresh marshes involve 

 special circumstances that are dependent upon specific management tech- 

 niques. The discussion concerning effects arising from decreases in land 

 elevation may not be applicable; the considerations contained in the sec- 

 tion of this report dealing with site access by canal may be more relevant, 



Although the above discussion assumes the fresh marsh is far removed from 

 brackish or saltwater influences, there may be specific cases where this 

 is not true. In those instances where marine-water inundation may occa- 

 sionally occur, the considerations and discussions must be appropriately 



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