Conservation > History & Loss

History and Loss

Wetland Loss Nationally (1780s to 2009)

Dahl (1990) estimated that in the 1780s the land area that is currently the lower 48 states of the United States of America contained about 220 million acres of wetlands. The most recent estimate, as of 2009, puts the total acreage of wetlands in the lower 48 states at 110 million acres – a loss of half of all wetlands. The largest driver of wetland loss before the 1970s was the practice of draining or tiling of wetlands for agriculture uses. Because wetland soils are quite useful for growing crops, many landowners drained their wetlands to utilize the land.

The estimates of wetland loss in the following table do not attempt to measure the quality or health of remaining wetlands, only the acreage. The following table aggregates all of the Status and Trends of Wetlands in the Conterminous United States data pertaining to freshwater wetlands from the 1950s estimates to the most recent 2009 report.

Wetland Losses Table (PDF)

The period of the 1950s to the 1980s saw the biggest losses in freshwater vegetated wetlands, with the estimated loss rate slowing in the late 1980s due largely to the “no net loss” rule implemented by President G. H. Bush in 1989. Pond acreage has increased over time due to the construction of stormwater retention ponds designed to moderate floods, ponds constructed as part of mining activities, as well as ponds constructed on private lands for cattle and livestock. While constructed ponds provide some of the same ecosystem functions as natural ponds (such as flood moderation) they rarely provide the full spectrum of ecosystem services at the same level as their natural counterparts.

Estimated average annual loss of freshwater wetland area, 1974 to 2009. Sources: Dahl and Johnson 1991; Dahl 2000; 2006; 2011.

Wetland Loss in Colorado

Dahl (1990) estimated that in the 1780s Colorado contained 2 million acres of wetlands, down to 1 million acres in the 1980s. These estimates are very general and may be underestimating Colorado’s wetland resource: CNHP’s wetland mapping (mostly mapping done in the 1970s/1980s) shows that with ~54% of the state mapped there are about 1.1 million acres of wetlands in the state. Because Colorado’s climate is quite dry, with more evapotranspiration than precipitation, wetlands are most commonly associated with riparian areas. As areas adjacent to rivers became settled, riparian wetlands were lost due to the development of the land adjacent to rivers as well as the diversion of water for irrigated agriculture. Similar to the eastern U.S., many of the prime agricultural areas in the state were in riparian floodplains and wet meadows created from natural springs. These wetlands were also drained and converted to agricultural use.