Ch. 2— Wetland Types • 27 



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Photo credit: Bob Friedman, OTA staff 



Waubesa marsh near Madison, Wis., began its development approximately 6,000 years ago with the filling in of a shallow 

 lake created by a retreating glacier. The majority of wetlands in the Northern United States were created 



by similar processes 



Activities of Man 



Wetlands may develop naturally adjacent to 

 resei-voirs, farm ponds, irrigation canals, and in pits 

 and depressions created by mining. Poor drainage 

 due to construction of highways, levees, and build- 

 ings also can lead to the development of wetlands. 

 Finally, manmade wetlands can be created inten- 

 tionally by Federal, State, and local resource agen- 

 cies and by conservation groups in shallow, pro- 

 tected waters. 



Miscellaneous Processes 



Wetlands may be formed by other special proc- 

 esses. In the Sandhills of Nebraska and in other 

 areas of the arid West, depressions have been 

 formed by wind action. The Everglades exist 

 because of a flow of ground water and surface water 

 over bedrock at and directly below the surface. In 

 Kentucky, Indiana, and several other States, wet- 

 lands are also found in sink holes and other areas 

 where bedrock has been dissolved by percolating 



