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IX. Wetland Numbers for Minnesota

How many and what types of wetlands do we have and where are they?

1) Anderson & Craig (Growing Energy Crops on Minnesota’s Wetlands: The Land Use Perspective, 1984) determined that there are 8.8 million acres of wetlands in Minnesota, compared to 18.6 million acres of original wetlands (see Appendix I1).  The amount of original wetlands is based on 1969 Land Use and Soils Data using 40 acre parcels.  Although this study is dated, it remains the only statewide estimate of original vs. remaining wetlands.

2) The National Wetland Inventory (NWI) maps include all waters and wetlands and rivers that have measurable area.  The NWI summary indicates approximately 10.6 million acres of wetlands currently exist in Minnesota (excluding water areas deeper than two meters).  Appendix I2 shows the distribution of wetland types across the state.  Most of this data was mapped during the period from 1982 through 1993 based on aerial photography done from 1974 through 1984.  The NWI maps exclude some farmed wetlands and may contain inaccuracies because of land use changes since they were developed.  Also, there are mistakes inherent when identifying certain types of wetlands with remote sensing methods.  Nonetheless, the NWI is the best and most current statewide data available for existing wetlands.  Digitization of the NWI data has been recently completed and information on obtaining versions of the NWI maps can be obtained by calling 1-800-USA-MAPS or on the Internet at http://www.nwi.fws.gov.  Paper copies of the NWI maps can be purchased from the Minnesota Bookstore by calling 1-800-657-3757 or 651-297-3000.

3) The Natural Resource Conservation Service has developed the National Resources Inventory (NRI), which is based on field sampling.  This study or inventory, which includes farmed wetlands, concluded from 1992 data that a total of approximately 10.6 million acres of wetlands (and 3.6 million acres of water areas deeper than two meters) remain in Minnesota, compared to an original number of 20+ million acres of wetlands.  The NRI data represents a statistical model that is accurate only at a very large scale and is not useful for field work or local planning efforts.  The NRI can be accessed on the Internet at http://www.mn.nrcs.usda.gov.  

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