108 • Wetlands: Their Use and Regulation 



ulate these activities are discussed in chapters 7, 

 8, and 9. Further elaboration on the reasons for 

 the major source of loss, due to converson to 

 agriculture is presented following the tables. 



Agricultural Conversions 



Information on Federal policy and national 

 trends in agricultural land use was obtained from 

 a working paper on agricultural policies prepared 

 for OTA, except where other sources are noted. 



Trends in Agricultural Conversions 



Eighty percent of freshwater wetland losses oc- 

 curring between the mid-1950's and the mid-1970's 

 were attributed to agricultural conversions, accord- 

 ing to NWTS data. Only 2 percent of estuarine wet- 

 lands were lost to agriculture during this 20-year 

 period. Conversions of estuarine wetlands to agri- 

 cultural use were greater prior to 1950. For exam- 

 ple, in the Snohomish Estuary of western Washing- 

 ton, conversion of wetlands to agricultural use was 

 greatest prior to 1940 but continued to increase at 

 a reduced rate untU about 1960 (14). In Califor- 

 nia, diking of northern coastal wetlands for 

 agriculture primarily occurred prior to 1950 (7). 

 Since that time, many of the diked former agricul- 

 tural areas have been filled for other uses. On the 

 east coast, former diked estuarine wetlands used 

 for agriculture have in many cases reverted back 

 to estuarine wetlands or been maintained for non- 

 agricultural purposes such as waterfowl production 

 (13). 



Although the general trend is the loss of wedands 

 to agriculture, there have been some relatively small 

 gains in wetlands from former agricultural lands. 

 Agriculture-related losses and gains of freshwater 

 vegetated wetlands were 11.7 million and 899,000 

 acres, respectively. Similar losses and gains of es- 

 tuarine wetlands were 9,000 and 2,000 acres, re- 

 spectively. Some parts of New England actually had 

 net gains in wetlands from agricultural land use. 

 Some of these agricultural lands have reverted to 

 wetland through lack of maintenance of former 

 drainage ditches. However, the majority of aban- 

 doned agricultural areas have been converted to 

 other nonwetland uses (17). 



Wedand conversion to agriculture almost always 

 involves surface drainage, but drainage may occur 

 in areas that are not wedands. USDA has prepared 

 estimates of surface and subsurface drainage of all 

 lands between 1900 and 1980. The data do not 

 cover wetlands separately. By examining these 

 drainage data in relation to NWTS estimates of 

 wetland loss to agriculture between the mid-1950's 

 and mid-1970's, it is possible to make some esti- 

 mates of wetland loss to agriculture between 1975 

 and 1980 on a nationwide basis. 



Pavelis (11) estimates that about 17 million acres, 

 or about 850,000 per year, were surface-drained 

 between 1955 and 1975 (table 22). During approx- 

 imately the same period of time, NWTS estimates 

 that 11 million acres of wetlands, about 550,000 

 acres/yr, were converted to agricultural land. This 

 amount represents about 65 percent of the surface 

 drainage. Between 1975 and 1980, just over 2 mil- 

 lion acres, or about 426,000 acres/yr, were sur- 

 face-drained. Even if all the drained lands were 

 wetlands, the rate of wetland conversion (requir- 

 ing surface drainage) has declined by at least 20 

 percent. However, if the proportion of drained wet- 

 lands to overall drained land has remained about 

 65 percent since 1975 the rate oi actual wedand con- 

 version to agricultural land would be about 275,000 

 acres/yr or about 50 percent of past wetland drain- 

 age rates. If gains in wetland acreage due to agri- 

 culture are proportional to those of the mid-1950's 

 to mid-1970's, nef conversion rates would be just 

 over 250,000 acres/yr. 



Interpretation of these nationwide figures may 

 be somewhat misleading. In the past, drainage was 

 concentrated in the Midwest, the Lower Mississippi 

 River Valley, and the Atlantic and Texas coasts. 

 More recently, although new drainage has been at 

 a virtual standstill in many parts of the country, 

 significant drainage activity still is taking place in 

 the Lower Mississippi River Valley, Florida, and 

 the Southeast in general (12). For example, data 

 from the Lower Mississippi River Valley show that 

 rates of clearing of bottom land hardwoods (which 

 is often accompanied by drainage for crop produc- 

 tion) continued to increase between 1967 and 1977 

 in Louisiana. Louisiana also had the greatest per- 

 centage of remaining forest in 1978. But in the five 



