CRS-143 



APPENDIX A: TRANSPORTATION FILLS— A CASE STUDY 

 Examining in more detail one type of activity that alters wetlands can 

 convey the complexity of studying effects of alterations on natural functions. 

 Fills for transportation purposes have been made all over the country in all 

 types of wetlands. Highways, railbeds, and airport runways have all been 

 constructed on wetland fills. Wetlands have been a preferred location for 

 these facilities in the past because of low land costs and ease of right-of-way 

 acquisition. Fills supporting causeways are generally the least expensive form 

 of construction across wetlands, so they have been the preferred engineering 

 technique when other values were not considered. Highway fills, In particular, 

 have been the subject of numerous studies during the past decade because of 

 conflicts between transportation development and wetland protection. A recent 

 study, prepared for the Federal Highway Administration, identified a number 

 of potential physical and biological impacts in wetland areas. The detailed 

 set of conclusions which follow below is representative of the growing under- 

 standing about wetland functions, and the range of potential effects associated 

 with wetland alterations. 



Physical Impacts : 



1. Change in mean water level — levels can be increased by the struc- 

 ture through damming effects or decreased through drainage, altering 

 wetland functions. 



2. Change in periodicity — many wetland species require a predictably 

 varied water regime. The extent and timing of fluctuations are im- 

 portant . 



3. Change in wetland circulatory patterns — wetland species have dif- 

 fering tolerances for nutrients and dissolved gases which are distri- 

 buted, in part, based on circulatory patterns. 



