Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/1/2007
Publication Date: 5/1/2008
Citation: Wren, D.G., Davidson, G.R., Walker, W.G., Galicki, S.J. 2008. The Evolution of an Oxbow Lake in the Mississippi Alluvial Floodplain. Journal of Soil and Water Conservation. 6(3): 129-135. Interpretive Summary: The effects of civilization and cultivation on watersheds can be measured by examining sedimentation in lakes and reservoirs. In the case of natural lakes, such as river oxbows, thousands of years of erosion history can be available. In order to date these older sediments, the decay of the Carbon-14 isotope is measured. Using this technique, approximately 5000 years of history of Sky Lake, a Mississippi River oxbow was examined. Several phases of the lake’s life were identified. The earliest phase began just after the lake was cut off from the Mississippi River system near 4100 years before 2006 (BP), extends to approximately 3600 BP, and is characterized by sedimentation rates of approximately 0.73 mm/yr. These relatively high sedimentation rates were likely caused by frequent flooding from the river channel when there was still a direct hydraulic connection between the river and the cutoff bend. In the next phase, extending from 3600-100 BP, isolation from the river channel, the low slope of the surrounding land, and the forested cover in the watershed resulted in sedimentation rates of approximately 0.17 mm/yr. From 100-4 BP, land clearing due to civilization and agriculture resulted in a sedimentation rate of 9 mm/yr.
Technical Abstract: The decay of 14C can be used to assign dates to ancient reservoir sediments, yielding valuable information on the erosion history of watersheds. The organic fraction of bulk sediments can be used in the absence of discrete sub-fossils to identify sedimentation rates in some locations. This method, along with the 14C dating of discrete sub-fossils, was used to reconstruct the history of Sky Lake, an oxbow cutoff in the Mississippi Alluvial Floodplain. Breaks in the slope of 14C activity can be readily explained by events in the history of Sky Lake. It was found that the lake was cut off from the Mississippi River system approximately 4100 years BP (relative to 2006). From 4100-3600 BP the sedimentation rate was 0.73 mm/yr, then from 3600-100 BP it was 0.17 mm/yr. From 100-4 BP, the rate went up to 9 mm/yr. The dates reported here are younger than those previously reported for Sky Lake, although they still place it in the Stage 2 Mississippi River meander belt.