Watershed disturbance history as interpreted through floodplain core analysis Big River Watershed, Ozark Highlands, Missouri.

Authors: Miranda Jordan*, Missouri State University, Robert T Pavlowsky, Missouri State University; Ozarks Environmental and Water Resources Institute
Topics: Geomorphology, Environmental Science, Land Use
Keywords: Legacy sediments, geochemistry, geomorphology, floodplain
Session Type: Paper
Day: 4/4/2019
Start / End Time: 9:55 AM / 11:35 AM
Room: Coolidge, Marriott, Mezzanine Level
Presentation File: No File Uploaded

Sediment and geochemical tracers can be used to assess the record of disturbance events and sedimentation histories in floodplain deposits. This study evaluates sedimentary and geochemical characteristics of legacy floodplain deposits that have accumulated over the past 170 years along Big River (2,500 km2) in southeast Missouri. Previous studies suggest soil erosion rates peaked during agricultural settlement period between 1850 and 1910. Big River also received large volumes of mine tailings released from the Old Lead Belt District which peaked in the early 1900s. Mining-contaminated legacy deposits from 1 to 4 meters thick are known to occur on floodplains along Big River. This is the first study to correlate historical floodplain deposition rates to mining, flood, and settlement records. Fifteen cores were collected along a cross-valley transect in the lower portion of the watershed in Jefferson County, Missouri. Geochemical analyses using X-ray Fluorescence indicates Pb/Ca ratios as well as Sr/Ti ratios can be utilized to determine tailings contributions to bulk sediment layers. Floodplain deposition rates were >2 cm/yr from settlement until 1930 and between 1 - 1.5 cm/yr from 1930 to present. Percent sand peaks in the core profile help chronicle the history of large flood events. The new core record developed for the lower Big River is compared to several other upstream sites located closer to the mining district. These analyses will add to our understanding of how river systems respond to land use and climate change in the Ozark Highlands.

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