Wetland Loss 1780s-1990s
Source: Environmental Protection Agency - Index of Watershed Integrity
Map Description:
Recent wetlands loss rates (Natural Resources Inventory (NRI), 1982-1992) were combined with historic loss rates (National Wetlands Inventory (NWI), 1780s-1980s) to form an index. The combined index is a more robust indicator of watershed condition than either loss rate used independently. Natural Resources Conservation Service (NRI) reports on wetland acreage on rural, non-federal lands that constitute about 75% of the Nation's land base. (Reported at 6-digit accounting unit)The U.S. Fish and Wildlife Service (NWI) maintains wetlands acreage data on federal and non-federal lands. (State level)

To create the Wetlands Loss Index, The IWI assigned the appropriate NWI State data to Accounting Units and combined it with NRI data. The following chart was used to assign scores (0 = low level of wetland loss, 1 = moderate level of wetland loss, and 2 = high level of wetland loss.

NRI: % loss between 1982 and 1992 (by 6 digit accounting unit)

<=0% 0-2% >2%
NWI: Historic % loss from
1780's to 1980's
(by State)
<30% 0 1 2
30-70% 1 1 2
>70% 2 2 2

Cautions for this Product:
Existing inventories of acreage change are national in scope and designed to provide information on national wetland losses and gains by wetland type. They were not designed to track wetland change on a watershed basis and, in most cases, do not prov ide robust State or watershed information. NWI and NRI were designed to answer different questions and have different sampling procedures. NRI data used in this analysis were adjusted to reflect differences and to account for some changes in NRCS's data collection methods. Unlike the other 14 IWI data layers, this data is reported at the 6-digit accounting unit scale (each 6-digit unit contains several 8-digit units), which IWI interpolated to the 8-digit area. .

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