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Cowardin System of Classification (1979) - National Wetlands Inventory
National Wetlands Inventory (NWI)
The National Wetlands Inventory (NWI) was established by the US Fish and Wildlife Service (FWS) in 1974 to conduct a nationwide inventory of U.S. wetlands to provide biologists and others with information on the distribution and type of wetlands to aid in conservation efforts. To do this, the NWI developed a wetland classification system (Cowardin et al. 1979) that is now the official FWS wetland classification system and the Federal standard for wetland classification.

The structure of this classification is hierarchal, progressing from Systems and Subsystems, at the most general levels to Classes, Subclasses and Dominance Types. Modifiers for Water Regime and Special Modifiers are applied to Classes, Subclasses and Subsystem.

The NWI also developed techniques for mapping and recording the inventory findings. The NWI relies on trained image analysts to identify and classify wetlands and deepwater habitats from aerial imagery. As computerized mapping and geospatial technology evolved, NWI discontinued production of paper maps in favor of distributing data via online "mapping tools" where information can be viewed and downloaded. Today, FWS serves its data via an on-line data discovery "Wetlands Mapper". GIS users can access wetlands data through an online wetland mapping service or download data for various applications (maps, data analyses, and reports). 

Source: U.S. Fish and Wildlife Service 

NWI Updated Maps and Data
The NWI maps and data for Blue Earth County were updated in 2015.  Information on the NWI update project  is available on the MN DNR Website

The updated GIS data can be downloaded from the Minnesota Geospatial Commons Website.   Metadata about the updated NWI data and maps are also available on the Minnesota Geospatial Commons Website. 

The Minnesota Department of Natural Resources is maintains an online map viewer for the updated NWI here.

National Wetlands Inventory Data Limitations, Exclusions and Precautions
The U.S. Fish and Wildlife Service's objective of mapping wetlands and deepwater habitats is to produce reconnaissance level information on the location, type and size of these resources. The maps are prepared from the analysis of high altitude imagery. Wetlands are identified based on vegetation, visible hydrology and geography. A margin of error is inherent in the use of imagery; thus, detailed on-the-ground inspection of any particular site may result in revision of the wetland boundaries or classification established through image analysis.

The accuracy of image interpretation depends on the quality of the imagery, the experience of the image analysts, the amount and quality of the collateral data and the amount of ground truth verification work conducted. Metadata should be consulted to determine the date of the source imagery used and any mapping problems.

Wetlands or other mapped features may have changed since the date of the imagery and/or field work. There may be occasional differences in polygon boundaries or classifications between the information depicted on the map and the actual conditions on site.

Exclusions - Certain wetland habitats are excluded from the National mapping program because of the limitations of aerial imagery as the primary data source used to detect wetlands. By policy, the Service also excludes certain types of "farmed wetlands" as may be defined by the Food Security Act or that do not coincide with the Cowardin et al. definition.

Precautions - Persons intending to engage in activities involving modifications within or adjacent to suspected wetland areas should seek the advice of appropriate federal, state, or local agencies concerning specified agency regulatory programs and proprietary jurisdictions that may affect such activities. Federal, state, and local regulatory agencies with jurisdiction over wetlands may define and describe wetlands in a different manner than that used in the National Wetlands Inventory (NWI).

Source: U.S. Fish and Wildlife Service 

REFERENCE: Classification of wetlands and deepwater habitats of the United States, Cowardin, L. M., Carter, V., Golet, F. C., and LaRoe, E. T. (1979), FWS/OBS-79/31, Reprinted 1992, U.S. Fish and Wildlife Service, Washington, DC