6 • Wetlands: Their Use and Regulation 





Box A. — Ecological Services of Wetlands 



Floodpeak Reduction. — Isolated and flood plain wetlands may temporarily store runoff, and flood 

 plain wetlands may slow the downstream flow of water and provide additional capacity for conveying flood- 

 waters, thus reducing floodpeaks and the frequency of flooding in downstream areas. For example, the 

 swampland in the Cache River watershed in southern Illinois retains about 8.4 percent of the watershed's 

 total runoff during flooding. 



Water-Quality Improvement. — By temporarily or permanendy retaining pollutants, such as suspended 

 material, excess nutrients, toxic chemicals, and disease-causing micro-organisms, wetlands can improve, 

 to varying degrees, the quality of the water that flows over and through them. Some poUutants that are 

 trapped in wedands may be converted by biochemical processes to less harmful forms. Some pollutants 

 may remain buried; others may be taken up by wedand plants and either recycled within the wetland or 

 transported from it. By temporarily delaying the release of nutrients until the fall, wedands may help pre- 

 vent excessive algal growth in open-water areas in the spring, when nutrient availability from other sources 

 is typically high. Wetlands can retain nutrients on a net annual basis and have been used successfully for 

 secondary treatment of sewage effluents. 



Food and Habitat. — Wedands provide food and habitat for many game and non-game animals. For 

 some species, wetlands are essential for survival. For instance, many species of waterfowl and freshwater 

 and saltwater fish require wetlands for breeding and nesting. Approximately 20 percent of all plant and 

 animal species listed by the Federal Government as threatened or endangered depend heavUy on wetlands. 

 For other species, wedands serve more general needs. Coastal marshes and certain types of inland, freshwater 

 wetlands achieve some of the highest rates of plant productivity of any natural ecosystem. This high pro- 

 ductivity often supports varied and abundant animal populations within a complex food chain. During 

 the growing season, less than 15 percent of the plant biomass in saltwater marshes is consumed directly 

 by foraging animals. After the plants die, up to 70 percent of the plamt material is broken down into small 

 particles and flushed into adjacent waters, where it becomes a potential food source for estuarine-dependent 

 fish and shellfish. 



Shoreline Stabilization. — Some vegetated saltwater and freshwater wedands significandy reduce 

 shoreline erosion caused by large waves and major coastal and riverine flooding. For exaunple, in a com- 

 parative study, an unvegetated shoreline retreated at a rate of more than twice that observed for a similar 

 shoreline fringed by a marsh. 



Ground Water Recharge. — Some wetlands that are hydrologically connected to a ground water system 

 supplement local or regional ground water supplies through infiltration/percolation of surface water. However, 

 the potential for most wetlands to recharge ground water is limited. In general, uplands are more effective 

 recharge areas than wetlands. 



Trends in Wetland Use 



Wetland conversion rates, which averaged 

 about 550,000 acres per year for the Nation be- 

 tween the mid-1950's and inid-1970's, vary sig- 

 nificantly throughout the country. On the one 



hand, conversion rates in the Lower Mississippi 

 River Valley were nearly three times the national 

 average; on the other hand, wetland conversions 

 occurred in coastal areas at rates that were about 

 25 percent less than inland conversion rates (table 



wetlands in areas that are not subject to a high de- 

 gree of wave action or swift currents. Most expe- 

 rience at creating new wetlands has been in rela- 

 tively calm coastal environments, where costs range 

 from as little as $250 to over $6,000 per acre. 



The ability to construct new wetlands or to 

 restore converted ones should not be used as sole 

 justification for converting wetlands to other 



uses: manmade wetlands do not necessarily pro- 

 vide the same values as natural ones. In addition, 

 it is probably not possible to create new wetlands 

 or to restore them at the rate they have been con- 

 verted to other uses in the past. 



