The National Resources Inventory (NRI) is a statistical survey of natural resource conditions and trends on non-Federal land in the
United States. Non-Federal lands include privately owned lands, tribal and trust lands, and lands controlled by state and local
governments.
The NRI provides nationally consistent statistical data on wetlands and deepwater habitats, including changes in extent of these
areas between 1992 and 2007. To assess conservation issues, this information must be analyzed in conjunction with other NRI data
elements.
Wetland ecosystems provide diverse services vital for environmental well-being, including food and habitat for wildlife and supporting
and regulating services -- such as nutrient cycling, delivery of fresh water, groundwater recharge, and mitigation of flooding.
Wetlands also have significant aesthetic, educational, and cultural values and provide opportunities for recreation
and tourism.
The findings presented here cover Palustrine and Estuarine wetlands and other aquatic habitats for the period 1992 to 2007
for the conterminous 48 States. Estimates do not include wetlands in Alaska, Hawaii, Puerto Rico, or on Federal lands. The NRI provides
information on systems and classes of wetlands, regional distributions,
and associated factors such as soils and land use. Of particular interest are trends in wetland gains and losses due to
agricultural activities.
The Cowardin et al. (1979) classification system recognizes five systems of wetlands and deepwater habitats. While there is
a wetland component in each of those Cowardin systems, these results do not include estimates for wetlands in Marine, Lacustrine, and
Riverine systems unless specifically identified separately as such. Estuarine wetlands are tidal
wetlands that are usually semienclosed by land, but have open, partly obstructed, or sporadic access to the open ocean,
and in which ocean water is at least occasionally diluted by freshwater runoff from the land. Palustrine wetlands include nontidal
wetlands dominated by trees,
shrubs, persistent emergent plants, or emergent mosses or lichens, as
well as small, shallow open water ponds or potholes. Palustrine wetlands
are often called swamps, marshes, potholes, bogs, or fens.
Palustrine and Estuarine wetlands covered 7 percent of the water and non-Federal land area of the conterminous 48 States in 2007,
accounting for nearly 111 million acres. (Table 6)
In 2007, Minnesota and Louisiana had the highest acreage of Palustrine and Estuarine wetlands. Minnesota had 10.9 million
acres (all Palustrine) and Louisiana had 10.2 million acres (7.7 million acres Palustrine; 2.5 million acres Estuarine).
(Table 1)
In 2007, there were 105.3 million acres of Palustrine wetlands and 5.4 million acres of Estuarine
wetlands in the conterminous 48 States. Deepwater habitats, made up of Lacustrine, Estuarine deepwater, Riverine, and Marine habitat
systems, totaled 48.5 million acres.
(Table 1)
Approximately 66 million acres, 60 percent of Palustrine and Estuarine wetlands, occurred on forest land in 2007.
Slightly less than 17 million acres, or 15 percent, occurred on cropland, pastureland, and Conservation Reserve Program (CRP)
land.
(Table 2)
Most states mirrored this composition with Maine and North Carolina having the highest percentage of their States' wetlands
in forest land in 2007.
(Table 2)
Three States had over 50 percent of their 2007 wetlands in cropland, pastureland, and CRP land: Idaho,
Kansas, and Iowa.
(Table 2)
Most wetlands occurred in the eastern half of the United States, particularly in the
Lake States, Southeast, and Delta States regions.
(Table 3)
In 2007, most Farm Production Regions had more wetlands in forest land than in other land uses. The exceptions were
the Northern Plains and Pacific regions, which had more wetland acreage in cropland, pastureland,
and CRP land; and the Mountain region, which had more wetland acreage in rangeland.
(Table 4)
Most Palustrine wetlands are vegetated, 94.8 million acres in 2007. Of these, 68.8 million acres are
dominated by trees or shrubs (forested and scrub-shrub) and 26.0 million acres are dominated by herbaceous vegetation (emergent).
(Table 5)
In 2007, approximately 10.5 million acres of wetlands were freshwater open wetlands without emergent vegetation (Palustrine other)
and almost 5.4 million acres were brackish water wetlands (Estuarine).
(Table 5)
Although the acreage of Palustrine and Estuarine wetlands declined from 1992 to 1997, during the two 5-year periods from 1997 to 2002
and 2002 to 2007 gross gains to wetlands were greater than gross losses. Although there was a net increase in wetlands from 1997 to 2002,
the net change from 2002 to 2007 was not significant at the 95 percent confidence level. See Margins of Error for more information.
(Table 6 and Table 10)
For the period 1992 to 1997, Palustrine and Estuarine wetlands had a 326,100 acre gain from uplands. This
was offset by a 482,400 acre loss to uplands, resulting in a net loss of 156,300 acres.
(Table 10)
For the period 1997 to 2002, Palustrine and Estuarine wetlands had a 395,800 acre gain from uplands. This
was offset by a 247,000 acre loss to uplands, resulting in a net gain of 148,800 acres.
(Table 10)
For the period 2002 to 2007, Palustrine and Estuarine wetlands had a 295,500 acre gain from uplands. This
was offset by a 194,100 acre loss to uplands. The net change is not significant, however, at the 95 percent confidence level.
See Margins of Error for more information.
(Table 10)
For both 5-year periods 1997 to 2002 and 2002 to 2007, gross gains to wetlands from agricultural lands were
greater than gross losses from wetlands on agricultural land. Conversely, gross losses of wetlands to development were greater
than gross gains.
(Table 10)
The two 5-year periods 1997 to 2002 and 2002 to 2007, also showed net gains to wetlands from other than
agricultural or development.
(Table 10)
The decade from 1997 to 2007 was the first decade in modern history in which a net gain in wetlands
was documented. There was an average annual gain in wetlands of 25,000 acres during this decade.
(Table 15)
During the 1997 to 2007 period, gross gains to wetlands totaled 691,100 acres. Most of these
gains, 410,200 acres, or 59.4 percent, were from agricultural lands. Only 15,200 acres, or 2.2 percent,
occurred on developed lands.
(Table 15)
Development was the major cause of wetland loss during the 1997 to 2007 period. Of the 441,100 acres of
gross losses, 266,000 acres, or 60 percent, were lost to development.
(Table 15)
The conterminous United States. has 242 coastal counties and 2,870 inland counties. Although coastal counties
represent only 7 percent of the surface area of the United States and 20 percent of the Palustrine and Estuarine wetlands,
they accounted for 30 to 39 percent of the wetland losses during the 1992 to 2007 period.
(Table 10, Table 11
and Table 13)
Coastal counties have 100 percent of the Estuarine wetlands. Most coastal Palustrine wetlands are dominated
by trees or shrubs (forested and scrub-shrub).
(Table 12)
Gross wetland losses in coastal counties decreased between 1992 and 2007, but gross gains were not
enough to offset the losses. Therefore, coastal counties showed a net loss in each 5-year period since 1992:
116,100 acres from 1992 to 1997, 65,100 acres from 1997 to 2002, and 56,100 acres from 2002 to 2007.
(Table 13)
For the period 1997 to 2007, most of the wetland losses in coastal counties were due to development: 84,900 acres
from 1997 to 2002 and 45,600 acres from 2002 to 2007.
(Table 13)
Gross wetland losses in inland counties also decreased during the 1992 to 2007 period. Gross wetland gains
increased from 1997 to 2002 but then decreased from 2002 to 2007.
(Table 14)
Inland counties showed a net wetland loss from 1992 to 1997 (40,200 acres) but net wetland gains from
1997 to 2002 (213,900 acres) and from 2002 to 2007 (157,500 acres).
(Table 14)
Similar to coastal counties, most of the wetland losses in the inland counties were due to development, but to a lesser
extent: 75,700 acres from 1997 to 2002 and 59,800 acres from 2002 to 2007.
(Table 14)
For the period 1997 to 2007, most of the wetland gains in the inland counties were due to agriculture:
211,600 acres from 1997 to 2002 and 174,500 acres from 2002 to 2007.
(Table 14)
Development resulted in the loss of 135,500 acres in the inland counties from 1997 to 2007
and 130,500 acres in the coastal counties.
(Table 15)
During the 10-year period 1997 to 2007, development was responsible for 76 percent of the wetland losses
in the coastal counties and 50 percent in the inland counties. Agriculture was responsible for only
6 percent of the wetland losses in the coastal counties and 21 percent of the losses in the inland counties.
(Table 15)
