31 



Recent Gains 



o 



< 



O 



LEGEND 



ini PALUSTRINE OPEN WATER 



I PALUSTRINE FLAT 



ESTUARINE WETLAND 



^ PALUSTRINE EMERGENT WETLAND 



|g PALUSTRINE SCRUB— SHRUB WETLAND 



V\ PALUSTRINE FORESTED WETLAND 



Fig. 28. Net losses and gains in wetlands of the conterminous U.S. 

 between the mid-50's and mid-70's (from Prayer, et al. 1983). 



Slight net gains in deepwater habitats — manmade 

 lakes and reservoirs and coastal waters — and in two 

 wetland types — inland flats and ponds — took place 

 between the mid-50"s and mid-70"s (Figure 28). Lake 

 acreage increased by 1 .4 million acres with 94% of this 

 gain occurring in the eastern half of the country. These 

 new lakes and reservoirs were mostly created from up- 

 lands, although vegetated wetlands were also destroyed. 

 Some new wetlands, however, have formed along the 

 edges of these new waterbodies. 



During the same period, coastal open waters increased 

 by 200,000 acres. Most of this gain came from Louisiana 

 at the expense of coastal wetlands which are being perma- 

 nently flooded at an accelerating rate. Causes of this 

 change from marsh to open water are numerous and com- 

 plicated and include natural rise of sea level, subsidence 

 of the coastal plain, levee construction, channelization, 

 and oil and gas extraction. 



Two wetland types experienced gains between the mid- 

 50's and mid-70's: inland flats and ponds. Two hundred 

 thousand acres of unvegetated wetland flats and 2. 1 mil- 

 lion acres of ponds were created. Pond acreage nearly 

 doubled from 2.3 million acres to 4.4 million acres, pri- 

 marily due to farm pond construction in the Central and 

 Mississippi Fly ways. Most of this pond acreage came 

 from former upland, although 145,500 acres of forested 

 wetlands and 385.000 acres of emergent wetlands were 

 changed to open water. 



Recent Losses 



Despite these modest gains, wetland losses were enor- 

 mous. In the mid-1950's, there were an estimated 108. 1 

 million acres of wetlands in the lower 48 states (Frayer, et 

 al. 1983). Just 20 years later, these wetlands were re- 

 duced to 99 million acres, despite some gains in wetlands 

 due to reservoir and pond construction, beaver activity, 

 and irrigation and marsh creation projects. This loss of 9 

 million acres equates to an area about three times the size 

 of Connecticut or twice the sizeof New Jersey. Actually, 

 1 1 million acres of our most valuable natural wetlands 

 were destroyed, but these acreage losses were minimized 

 by gains of 2 million acres of newly created wetlands, 

 giving a net loss of 9 million acres. The average rate of 

 wetland loss from the mid-50's to the mid-70"s was 

 458,000 acres per year: 440,000 acres of palustrine losses 

 and 18,000 acres of estuarine wetland losses. This annual 

 loss equals an area about half the size of Rhode Island. 



Agricultural development involving drainage was re- 

 sponsible for 87% of recent national wetland losses, 

 while urban development and other development caused 

 only 8% and 5%- of the losses, respectively (Figure 29). 

 Agriculture had the greatest impact on forested wetlands 



