CRS-144 



4. Alteration of local water table levels — changes in water table 

 levels often occur simultaneously with surface water alteration; 

 most wetlands depend on high water table levels. 



5. Drainage of surface water — resident and migratory species are 

 affected when surface water is removed; restoration may be slow and 

 difficult. 



6. Elimination of periodic flooding and fertilization — stabilization 



of water levels or elimination of periodic flooding will reduce pro- 

 ductivity. 



7. Change in retention storage — increase or decrease of flow downstream — 

 wetlands regulate local hydrology by diminishing peak flows and sup- 

 porting minimum flows; effects of wetland alteration that affect this 

 quality may be observed at some distance from the site. 



8. Damping of tidal variation — wetland plants are adapted to tidal 

 patterns, which influence water level periodicity and salinity 

 gradients. 



9. Alteration of salinity patterns — distribution of species in 

 coastal wetlands is dependent on the salinity gradient; gradient 

 changes can cause major shifts in species composition and habitat, 

 and affect estuarine food chains. 



10. Turbidity — excess suspended solid, inorganic and organic byproducts 

 of almost all phases of highway construction and use adversely affect 

 aquatic primary productivity, and feeding, reproductive, and migratory 

 success of higher organisms. 



11 . Sedimentation — sediments deposited on bottom plants and animals can 

 greatly reduce their survival and productivity. 



12. Chemical pollution — the potential for chemical pollution exists at 

 all phases of highway construction and use; the severity of the im- 

 pact may be moderated by the water regime, precipitation patterns, 

 topography, and the sensitivity of organisms to the pollutant. 



13. Change in temperature patterns — impoundment can increase the sur- 

 face temperature of water; in summer, higher temperatures may ex- 

 ceed resident species' thermal tolerance; some fish and shellfish 

 species are affected by changes of less than 5 degrees. 



Biological Impacts : 



1. Change in wetland size — changes in mean levels and periodicity of 

 water will elevate or lower water levels, causing the wetland to 

 grow or shrink as measured by shifts that indicate the edge of the 

 wetland. 



