Indiana Biological Survey
Aquatic Research Center
Division of Fishes Projects
Interior River Lowland Ecoregion
The Interior River Lowland (IRL) has varied land use including forestry, diverse cropland agriculture, orchards, livestock production, and oil and gas production. The IRL consists of dissected glacial till plain that is covered by thick mantle loess, rolling narrow ridgetops, and hilly to steep ridge and valley slopes. The IRL elevation ranges from 128.4-189.7 m, while local relief varies between 1 m of the till plain to 32.6 m on the rolling ridges, to about 197.6 m on prominent ridges. Stream valleys in the hills are often intermittent becoming perennial when they reach the valley floor. Large watersheds in the IRL often drain as much as 350 sq miles throughout the 19,000 sq miles of the ecoregion. Elevation varies from about 119.6 m in the southern portion of the ecoregion to over 299.4 m on a few hills in the north. Precipitation occurs mainly during the freeze period and averages from 39-46 inches annually. The ecoregion has lakes, reservoirs, and numerous scattered ponds (Omernik and Gallant 1988).
Both perennial and intermittent streams are common in the ecoregion. Constructed drainage ditches and channelized streams further assist in soil drainage in flat, poorly drained areas. Stream density is approximately two miles per square mile in the most typical portions of the ecoregion.
The IRL has a diverse assemblage of land use including farmland, which is used for feed grains, and hay for livestock. Some corn, soybeans, and red clover seed are also grown. Undrained soils are used for forage crops, pasture or timber (almost 35% of the ecoregion is forested). Emphasis on mixed farming, livestock, and some orcharding and some grape vineyards occurs on upland sites. Mostly beef cattle, swine, and chickens are raised.
Most of the better drained soils of the IRL ecoregion are generally light in color and moderately acidic. Hapludolls are dominant soil groups in silty loess, glacial tills, and sand aeolian materials. Fragiudalf’s have formed on some silt-covered ridgetops. Paleudalphs are common on old limestones. Shallow hapludolls occur on steep slopes. Udifluvents, Fluvaquents, and Haplaquolls are found in poorly drained floodplains.
The natural vegetation of the area consists of oak-hickory forests. White oak, black oak, northern red oak, bitternut hickory, shagbark hickory, yellow popular, white ash, sugar maple, and black walnut occurs on well-drained soils. Pin oak, shingle oak, and sweetgum occur on wet sites. Riparian areas support pin oak, silver maple, cottonwood, willow, sycamore, elm, sweetgum, ash, and river birch.
Fish Assemblage and Watershed Condition
Indiana Biological Survey - Aquatic Research Center
6440 S. Fairfax Rd., Bloomington, IN 47401
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