120 • Wetlands: Their Use and Regulation 



cess to oil and gas development sites also has con- 

 tributed significantly to direct and indirect wetland 

 losses in coastal Louisiana (15). While many early 

 studies attributed these losses to the presence of 

 levees on the Mississippi River, which reduced the 

 sediments contributing to the buildup of deltas and 

 wetlands (8), several recent studies in the Mississip- 

 pi Delta have shown a positive correlation between 

 canal density and the extent of wedand loss (13,53). 

 In addition to direct wedand loss resulting from the 

 disposal of dredged material along canal banks, the 

 increase in canal density in an area leads to more 

 saltwater intrusion into wetlands as water is flushed 

 in and out by the tides. Salinity changes may kill 

 vegetation, and tidal flows help erode the banks of 

 canals, causing them to widen at the annual rates 

 of from 2 to 14.8 percent per year. At the high an- 

 nual rate, a canal would double its width in only 

 4.7 years. 



Excavation commonly is used for mining and to 

 create dugouts, or reuse pits, for irrigation. Min- 

 ing for minerals such as peat, phosphate, and lime- 

 rock will cause total removal of wetland vegetation 

 overlying these deposits (30). Additional adverse 

 impacts also may result. For example, after lime- 

 rock was excavated and removed from the Biscayne 

 Aquifer in southern Florida, ground water filled 

 the pits left by the excavation, lowering the water 

 table. The stockpiling of materials, the construc- 

 tion of access roads, and other fUling associated with 

 development and operation of a mine also block sur- 

 face waterflows. Water-filled rockpits, which are 

 attractive locations for residential development, can 

 become degraded quickly by urban runoff. In ad- 

 dition, water in the open pit is subjected to con- 

 tinuous, year-round evaporation (9). 



In another example, the number and size of wet- 

 lands in the Rainwater Basin in Nebraska have 

 been reduced through the excavation of "dugouts," 

 or irrigation reuse pits. This practice results in par- 

 tial drainage of some wetlands and the flooding of 

 others (22). These wedand losses subsequendy have 

 led to increased incidence or risk of disease to water- 

 fowl, reduction in food supply for migratory birds, 

 and loss of breeding and rearing habitat for birds 

 (22). 



Filling 



The immediate and permanent effect of filling 

 is to bury wetland vegetation, increase the eleva- 

 tion of the area, and eliminate the periodic inun- 

 dation of the wetland (14). Several types of solid 

 waste are used as fill material. Municipal waste, 

 including household refiise and incinerator residue, 

 has been used for wetland fills. Construction and 

 demolition debris is used occasionally, as are stone, 

 sand, gravel, and broken concrete from highway 

 construction. Even coal ash has been disposed of 

 as fill in wetlands (8). The disposal of some types 

 of solid waste in wetlands carries the risk of detri- 

 mental chemical effects owing to leaching of nu- 

 trients and toxic chemicals from the fill material. 



For example, filling is a major factor associated 

 with wedand loss for land-leveling and agricultural 

 conversion in Nebraska and California; for con- 

 struction of impoundments in New England, the 

 Lower Mississippi River Valley, Lower Colorado 

 River Valley, South Carolina, and North Carolina; 

 for canal construction and dredged-material dispos- 

 al in coastal Louisiana, Mississippi, and Texas; for 

 port, harbor, and other coastal development; for 

 urban and industrial development in South Caro- 

 lina, New Jersey, California, New England, south 

 Florida, Washington, and Alaska; for road con- 

 struction in Alaska, New England, and Nebraska; 

 and for disposal of waste products in Washington, 

 California, and New England. 



Filling often is associated closely with dredging 

 and excavation activities. For example, the major 

 method used in the Southeast to create waterfront 

 real estate has been to excavate canals within wet- 

 lands, using the dredged material as fill for buUding 

 sites. This practice not only results in complete loss 

 of the wetland but also creates canals that are poor 

 habitat for both flora and fauna (26). A comparative 

 study of a residential lagoon system and natural 

 wedands has shown that the lagoon supports smaller 

 fish and shellfish communities (28). 



Highways built on fill material can have indirect 

 impacts by either flooding or dewatering adjacent 

 wedands. Culverts normally constructed at soil level 



