Chapter 5 



Wetland Trends 



CHAPTER SUMMARY 



Within the last 200 years, 30 to 50 percent of the 

 wetlands in the lower 48 States have been converted 

 by activities such as agriculture, mining, forestry, 

 oil and gas extraction, and urbanization. About 90 

 million acres are covered now by wedands. Accord- 

 ing to the most recent Federal survey, approximate- 

 ly 11 million acres of wedands in the lower 48 States 

 were converted to other uses between the mid- 

 1950's and mid-1970's. This amount was equiva- 

 lent to a net loss each year of about 550,000 acres, 

 or about 0.5 percent, of remaining wetlands. Pres- 

 ent nationwide rates of wetland conversion are 

 about half of those measured in the 1950's and 

 1960's. This reduction is due primarily to declin- 

 ing rates of agricultural drainage and secondarily 

 to government programs that regulate wedands use. 

 While coastal wetlands are protected reasonably 

 well through a combination of Federal and State 

 regulatory programs, inland, freshwater wetlands, 

 which comprise 95 percent of the Nation's wedands, 

 generally are not well protected. 



Wedand conversion rates and activities vary sig- 

 nificantly throughout the country. On the one 

 hand, conversions in the Lower Mississippi River 

 Valley occurred between the mid- 1 950 's and mid- 

 19 70' s at rates that were nearly three times the na- 



tional average; on the other hand, rates in the At- 

 lantic coast (exclusive of Florida) were only 30 per- 

 cent of the national average. Overall, wetland con- 

 versions occurred in coastal areas at rates that were 

 about 25 percent less than inland conversion rates. 



Ninety-seven percent of actual wedand losses oc- 

 curred in inland, freshwater areas during this 20- 

 year period. Agricultural conversions involving 

 drainage, clearing, land leveling, ground water 

 pumping, and surface water diversion were respon- 

 sible for 80 percent of the conversions. Of the re- 

 mainder, 8 percent resulted from the construc- 

 tion of impoundments and large reservoirs, 6 per- 

 cent from urbanization, and 6 percent from other 

 causes, such as mining, forestry, and road construc- 

 tion. Fifty-three percent of inland wetland conver- 

 sions occurred in forested acres, such as bottom 

 lands. Of the actual losses of coastal wetlands, ap- 

 proximately 56 percent resulted from dredging for 

 marinas, canals, port development, and to a lesser 

 extent from erosion; 22 percent resulted from ur- 

 banization; 14 percent were due to dredged-materi- 

 al disposal or beach creation; 6 percent from natural 

 or man-induced transition of saltwater wedands to 

 freshwater wetlands; and 2 percent were from agri- 

 culture. 



NATIONAL TRENDS— NET LOSS AND GAIN 



According to the National Wedand Trends Study 

 (NWTS) (8), conducted recently by the U.S. Fish 

 and Wildlife Service (FWS), there were in the mid- 

 1970's approximately 99 million acres of vegetated 

 and unvegetated wedands in the United States, ex- 

 clusive of Alaska and Hawaii. * Saltwater (or estua- 



"Alaska and Hawaii were not included in NWTS. However, the 

 Alaska District of the Corps of Engineers estimates that there may 

 be as many as 223 million acres of wetlands in Alaska, nearly 60 per- 

 cent of the State. Almost half of this potential wetland acreage (98 

 million acres) is some type of tundra. Overall, the loss of wetlands 

 in Alaska has not been great, although it has been concentrated in 

 a few locations. Figuies for Hawaii were not obtained but are expected 

 to be quite low in relation to the data for the lower 48 states. 



rine) wedands comprise 5 percent of the wetlands; 

 the rest are freshwater wetlands. (See table 1 1 for 

 the relationship between the wetland types de- 

 scribed in this chapter and those discussed in ch. 

 1 .) About 93 million acres are vegetated types, in- 

 cluding areas dominated by emergent plants (emer- 

 gent wedands), large trees (forested wedands), and 

 shrubs and small trees (scrub/shrub wedands). Be- 

 tween the mid-1950's and mid-1970's, there was 

 a net loss of these vegetated wetlands of approx- 

 imately 1 1 mOlion acres (fig. 6). Ninety-seven per- 

 cent of this net loss was attributed to freshwater wet- 

 lands. 



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