Wetlands occur in and provide benefits to every county in Indiana. The lack of quantitative information on some aspects of Indiana's wetland resources is a major obstacle to improving wetland conservation efforts.
The most extensive database on wetland resources in Indiana is the National Wetlands Inventory developed by the U.S. Fish & Wildlife Service. In 1985, the Indiana Department of Natural Resources, Division of Fish and Wildlife entered into a cooperative agreement with the U.S. Fish and Wildlife Service to share the costs of mapping Indiana's wetlands.
Indiana's National Wetlands Inventory maps were produced primarily from interpretation of high-altitude color infrared aerial photographs (scale of 1:58,000) taken of Indiana during spring and fall 1980-87. Map production also included field investigations, reviews of existing information, quality assurance, draft map production, interagency review of draft maps, and final map production.
National Wetland Inventory maps indicate wetlands by type, using the Cowardin et al. classification scheme (1979, Classification of wetland and deepwater habitats of the United States, U.S. Fish and Wildlife Service FWS/OBS-79/31). The minimum size of a given wetland on National Wetland Inventory maps is typically one to three acres. Very narrow wetlands in river corridors and wetlands under cultivation at the time of mapping are generally not depicted, and forested wetlands are poorly discriminated.
The most recent and complete analysis of this database was conducted in 1991 by the Indiana Department of Natural Resources. This report, prepared by Robert Rolley, Wildlife Research Biologist, is entitled "Wildlife Management and Research Notes, #532, Indiana's Wetland Inventory." According to the report, Indiana had approximately 813,000 acres of wetland habitat in the mid-1980s when the data were collected. Wetland loss or gain since then is unknown.
The following figures are from the Indiana Department of Natural Resources report:
| Chart 1: Wetland acreage estimates for Indiana during the 1980's by wetland type | ||
|---|---|---|
| Wetland habitats | Acres | % of total |
| scrub-shrub | 42,131 | 5.2% |
| forested | 504,336 | 62.0% |
| wet meadow | 55,071 | 6.8% |
| shallow marsh | 67,564 | 8.3% |
| deep marsh | 20,730 | 2.5% |
| open water | 98,565 | 12.1% |
| other | 24,633 | 3.0% |
| Total wetland habitats | 813,032 | 100% |
Palustrine wetlands were also classified according to duration of flooding. "Temporarily flooded" was the most common duration of flooding. Approximately 460,000 acres or 57% of palustrine habitats were classified as temporarily flooded. "Seasonally flooded" was the next most common - 220,000 acres (27%), followed by "intermittently exposed" - 80,000 acres (10%), "semi-permanently flooded" - 40,000 acres (5%), and "saturated" - 24,000 acres (3%). For a county by county breakdown of Indiana's wetland resources in the mid-1980's, view Chart 2.
The IDNR project confirmed that the major concentration of wetlands was in the northeastern portion of Indiana, along river floodplains in southwestern Indiana, and in the Lake Michigan shoreline region in northwestern Indiana. Noble County contained the greatest number of wetland acres with approximately 27,500 acres or 3.38% of the state's total wetland acreage. Ohio County contained the least amount of wetland area with 633 acres or only 0.08% of the states total wetland acreage. Forested wetlands were the most common type of wetland in all 92 counties.
The best estimate of the wetlands in Indiana before settlement 200 years ago is an assessment based on hydric soils (soils indicative of wetlands) conducted by the USDA Soil Conservation Service (now the Natural Resource Conservation Service). Based on an analysis of this data by the Indiana Department of Natural Resources, there were approximately 5.6 million acres of wetlands in Indiana 200 years ago. Combining the information from the National Wetlands Inventory and the IDNR yields the following summary:
- Estimated wetlands circa 1780s: 5,600,000 acres
- Percent of surface area in wetlands circa 1780s: 24.1%
- Existing wetlands: 813,000 acres
- Percent of surface area in wetlands today: 3.5 %
- Percent of wetlands lost: 85%
The Department of Environmental Management received grant approval to investigate trends in wetlands losses and gains. Part of this study will focus on regulatory activities, another part on conservation efforts, and a final part devoted to recreating the work carried out by IDNR in the 1980's utilizing more recent information and newer habitat studies.