Geology and Geomorphology
The Chariton River basin is within the Glaciated Plains region of Missouri and Iowa (Unklesbay and Vineyard 1992), also known as the Dissected Till Plains (COE 1963, Figure Ge01). In describing the geological origins of the basin, we start at the bottom of a stratum that exists 350 to 600 feet into the earth. Up to 250 feet of limestone was deposited in the Mississippian age (MDNR unpublished). Above the limestone are deposits of Pennsylvanian-age sedimentary rock in layers up to 170 feet thick. These were formed under rapidly changing conditions that caused sediments to be deposited in alternating sequences (e.g., shale, coal, limestone etc., Figure Ge02) (Unklesbay and Vineyard 1992).
The basin contains coal deposits of the Pennsylvanian age (MDNR unpublished), yet not all of it has commercial value. Of the five minable coal fields in Missouri, two lie partially within the boundaries of the Chariton River basin (Unklesbay and Vineyard 1992). The "Plains" of the Glaciated Plains are the deposits that were left on top of the Pennsylvanian strata by glaciers--a level expanse of till or drift up to 200 feet deep composed of mostly clay with rock fragments and sand lenses (MDNR unpublished). Erosional forces cut steep relief into this landscape prior to it being covered by wind deposited loess (Unklesbay and Vinyard 1992), which varies in thickness to eight feet. Soils of loessal origin are found primarily on the tops of ridges (SCS 1995, 1994, 1991, 1989).
The prevalent soil types that developed from this loess and till parent material are classified as loams with differing clay and silt content. Soils with silt content are predominantly alluvial in origin. The relatively low permeability of the soil and till coupled with the presence of shale and coal greatly inhibits the percolation of surface water to ground water sources. Because of this, most water movement occurs through the stream network.
Of the mappable soil units in Putnam, Adair and Macon counties, 57% to 71% were classified as "eroded" or "severely eroded" (SCS 1995, 1994, 1991). The streams of the basin have served as depositories for these eroded soils. The bed of the Chariton River mainstem is comprised almost exclusively of unconsolidated sand.
Though the stream resource remains very degraded, soil erosion has been reduced significantly in the past ten years. In a 1982 report it was noted that 56% of land in the Chariton River basin was losing 8, 15 or 22 tons of soil per acre annually depending upon soil type (USDA 1982). An inventory by the Soil Conservation Service revealed that mean soil loss rate per acre of Missouri farmland dropped from 9.4 tons in 1982 to 5.5 tons in 1992 (SCS 1995). Ninety percent of the reduction occurred on cropland. Breaking this figure down, 47% was attributable to implementation of conservation practices on highly erodible cropland, 35% was due to cropland going into the Conservation Reserve Program (CRP), 10% was attributable to soil loss reductions on lands not classified as highly erodible, and 9% was attributed to other sources. In a watershed where the majority of land is in some type of commodity production, wise land management is crucial to the quality of stream habitat and health of the aquatic communities they support.
Stream Channel Gradients
Channel gradients (slopes) were determined for all third-order and larger streams by using USGS 7.5-minute topographic maps and digitizing software (Table Lo01). Gradient is very low (2.2-3.1 feet/mile) in the mainstem Chariton River; and it is equally low (1.0-3.3 feet/mile) in the lowermost reaches (orders 4-5) of major basin tributaries ? Middle Fork Little Chariton River, East Fork Little Chariton River, and Mussel Fork Creek. Gradients in fourth-order reaches of other basin streams range from 1.4 to 10.4 feet/mile. Such low gradients lend themselves to deposition of sediments transported from the watershed