Causes of Wetland Losses

Causes of Palustrine and Estuarine Wetland Losses between 1992 and 1997, by NRCS Region

Thumbnail version of the map. Select for a popup of the full sized map.


This map shows wetland loss and reasons for wetland conversion from 1992 to 1997. The pie charts indicate the reasons for wetland conversion. Pies are proportional to the amount of wetland loss. Nationally, development accounted for 49% while agriculture accounted for 26%. Net wetland losses averaged 32.6 thousand acres per year between 1992 and 1997. Agriculture includes cropland, pastureland, CRP, and other farmland. Development includes urban areas and rural transportation land. Silviculture includes all non-Federal forest land. Miscellaneous includes rangeland and all other land uses. Wetlands includes palustrine and estuarine wetlands identified using the cowardin system, it does not include deepwater habitats. Shifts between wetlands and other aquatic systems are not considered either gains or losses. Hawaii is included in the West region. Puerto Rico and the U.S. Virgin Islands are included in the Southeast region.

Cautions for this Product:
Shifts between wetlands and other aquatic systems are not considered either gains or losses. The map does not include deepwater habitats or wetlands on Federal Land. Data are not collected on Federal land.


Source: National Resources Inventory, 1997
Distributor: USDA-NRCS-RIAD
NRI sample data are generally reliable at the 95% confidence interval for state and certain broad substate area analyses. Generally, analyses that aggregate data points by smaller geographic areas and/or more specific criteria result in fewer data points for each aggregation and therefore less reliable estimates. NRI maps reflect national patterns rather than site- specific information.


Aggregate Layer: NRCS Regions
Other Layers Displayed: State


Conservation Reserve Program (CRP):
A Federal program established under the Food Security Act of 1985 to assist private landowners to convert highly erodible cropland to vegetative cover for 10 years. [NMCSP]

Cowardin system:
A classification system of wetlands and deep water habitats of the United States, officially adopted by the U.S. Fish and Wildlife Service (FWS) used to develop wetland data bases. The system was developed by Lewis M. Cowardin of the U.S. Fish and Wildlife Service and others. The five major systems are recognized in the NRI: Estuarine, Lacustrine, Marine, Palustrine, and Riverine. [USFWS]

A Land cover/use category that includes areas used for the production of adapted crops for harvest. Two subcategories of cropland are recognized: cultivated and noncultivated. Cultivated cropland comprises land in row crops or close-grown crops and also other cultivated cropland, for example, hayland or pastureland that is in a rotation with row or close-grown crops. Noncultivated cropland includes permanent hayland and horticultural cropland. [NRI-97]

Deepwater habitat:
Any open water area in which the mean water depth exceeds 6.6 feet in nontidal areas or at mean low water in freshwater tidal areas, or is covered by water during extreme low water at spring tides in salt and brackish tidal areas, or covers the deepest emerging vegetation, whichever is deeper [USFWS]

Developed land:
A combination of land cover/use categories, Urban and built-up areas, and Rural Transportation Land.

Estuarine system:
Deepwater tidal habitats and adjacent tidal wetlands that are 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. [USFWS]

Federal land:
A land ownership class designating land that is owned by the Federal Government. It does not include, for example, trust lands administered by the Bureau of Indian Affairs nor Tennessee Valley Authority (TVA) land. No data are collected for any year that land is in this ownership. [NRI-97]

Forest land:
A Land Cover/Use that is at least 10 percent stocked by single stemmed forest trees of any size which will be at least 4 meters (13 feet) tall at maturity. When viewed vertically, canopy cover is 25 percent or greater. Also included are areas bearing evidence of natural regeneration of tree cover (cutover forest or abandoned farmland) and not currently developed for nonforest use. For classification as forest land, an area must be at least one acre and 100 feet wide. [NRI-97]

Palustrine system:
All non-tidal wetlands dominated by trees, shrubs, persistent emergents, emergent mosses, or lichens, and all such wetlands that occur in tidal areas where salinity due to ocean derived salts is below 0.5 percent [U.S.FWS]

Pastureland and Native Pasture:
A Land Cover/Use category of land managed primarily for the production of introduced or native forage plants for livestock grazing. Pastureland may consist of a single species in a pure stand, a grass mixture or a grass-legume mixture. Management usually consists of cultural treatments-fertilization, weed control, reseeding, or renovation and control of grazing. (For the NRI, includes land that has a vegetative cover of grasses, legumes, and/or forbs, regardless of whether or not it is being grazed by livestock.) [NRI-97]

A Land cover/use category on which the climax or potential plant cover is composed principally of native grasses, grasslike plants, forbs or shrubs suitable for grazing and browsing, and introduced forage species that are managed like rangeland. This would include areas where introduced hardy and persistent grasses, such as crested wheatgrass, are planted and such practices as deferred grazing, burning, chaining, and rotational grazing are used, with little or no chemicals or fertilizer being applied. Grasslands, savannas, many wetlands, some deserts, and tundra are considered to be rangeland. Certain communities of low forbs and shrubs, such as mesquite, chaparral, mountain shrub, and pinyon-juniper, are also included as rangeland. [NRI-97]

Areas that have a predominance of hydric soils and that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and under normal circumstances do support, a prevalence of hydrophytic vegetation typically adapted for life in saturated soil conditions. [NFSAM]

Wetland System:
Complex of wetland habitats that share the influence of similar hydrologic, geomorphologic, chemical, or biological factors. [U.S. FWS]

Product Information

Product ID: 5818
Production Date: 12/12/00
Product Type: Map

For additional information contact the Resources Inventory and Assessment Division. Please include the Product ID you are inquiring about. or 1400 Independence Avenue SW - P.O. Box 2890 - Washington D.C. 20013. If you use our analysis products, please be aware of our disclaimer.