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Wabash-Ohio Bottomlands

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About the Wabash-Ohio Bottomlands

The Wabash-Ohio Bottomlands is a relatively narrow, long, and branching region that extends along much of the Wabash and Ohio rivers, in southern Illinois, southwestern Indiana, and the northern border of western Kentucky.

This region consists of a nearly level-floodplain surrounding low-gradient rivers, and adjacent terraces, oxbow lakes, and wetlands. There are some low ridges. Parts of this region in the north were glaciated, and there is some glacial outwash, but most of the soils here are formed on alluvium. The bedrock is of shale and sandstone, with some limestone, but outcroppings are rare. The climate is humid and subtropical, and is among the mildest in the general region, with a frost free period of 180-200 days.

Historically, this region was covered with bottomland hardwood forests or southern floodplain forest, with some wet and mesic prairies. There was also some beech forest on the better-drained sites, as well as swamps, ponds, and sloughs. Much of the reason experienced regular seasonal flooding. Details of the original vegetation are not well-documented, but bottomland forests probably had associations of pin oak (Quercus palustris), bur oak (Quercus macrocarpa), Shumard's oak (Quercus shumardii), and swamp white oak (Quercus bicolor) and forested swamps featured bald cypress (Taxodium distichum) and water tupelo (Nyssa aquatica), especially in the Cache river basin.

This region has been altered by flood control, including channelization and drainage ditches, and most of the forests have been cleared. There is extensive agriculture here, which produces corn, soybeans, wheat, alfalfa (especially in the south) and livestock. In spite of flood control efforts, the water table is still seasonally high and localized flooding is common. There is significant oil and gas extraction, and some mining of sand and gravel. Some woodlands and wetlands remain, but only at a small fraction of their original extent. Most of the land that is left wild is on sites that are either too poorly-drained, or have drought-prone sandy soils.

Most of this region is bordered to the west by the Wabash River Bluffs and Low Hills, and past that, the Southern Illinoian Till Plain. In the north, this region is bordered to the east by the Glaciated Wabash Lowlands, a region covered in highly leached glacial till. South of this, the region is bordered to the east, and in the east, surrounded to the north and south by the Green River-Southern Wabash Lowlands. The far south of this region mostly surrounds the Cretaceous Hills and is bordered to the north by the Southern Shawnee Hills and to the south by the Loess Plains. There is also a small border to the southeast with the Crawford-Mammoth Cave Uplands and an even smaller one with the Caseyville Hills. Just north of this there is a small border to the west by the Northern Shawnee Hills, which are surrounded by this region in one place.

References

1. Woods, A.J, Omernik, J.M., Brockman, C.S., Gerber, T.D., Hosteter, W.D., Azevedo, S.H. "Ecoregions of Indiana and Ohio (Poster)", US Geological Survey (1998) Web.

2. Woods, A.J., Omernik, J.M., Martin, W.H., Pond, G.J., Andrews, W.M., Call, S.M, Comstock, J.A., and Taylor, D.D. "Ecoregions of Kentucky (Poster)", U.S. Geological Survey, Reston, VA (2002) Web.

3. Woods, A.J., Omernik, J.M., Pederson, C.L., Moran, B.C. "Level III and Level IV Ecoregions of Illinois", U.S. Environmental Protection Agency, Washington, DC (2006) Web.