Paleoreconstruction of organic carbon inputs to an oxbow lake in the Mississippi River watershed : effects of dam construction and land use change on regional inputs

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Date
2015-10-10
Authors
Bianchi, Thomas S.
Galy, Valier
Rosenheim, Brad E.
Shields, Michael
Cui, Xingqian
Van Metre, Peter
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DOI
10.1002/2015GL065595
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Keywords
Organic carbon cycling
Paleoreconstruction
Dam reservoirs
Biomarker proxies
Abstract
We use a dated sediment core from Lake Whittington (USA) in the lower Mississippi River to reconstruct linkages in the carbon cycling and fluvial sediment dynamics over the past 80 years. Organic carbon (OC) sources were characterized using bulk (δ13C, ramped pyrolysis-oxidation (PyrOx) 14C, δ15N, and TN:OC ratios) and compound-specific (lignin phenols and fatty acids, including δ13C and 14C of the fatty acids) analyses. Damming of the Missouri River in the 1950s, other hydrological modifications to the river, and soil conservation measures resulted in reduced net OC export, in spite of increasing OC concentrations. Decreasing δ13C values coincided with increases in δ15N, TN:OC ratios, long-chain fatty acids, and lignin-phenol concentrations, suggesting increased inputs of soil-derived OC dominated by C3 vegetation, mainly resulting from changes in farming practices and crop distribution. However, ramped PyrOx 14C showed no discernible differences downcore in thermochemical stability, indicating a limited impact on soil OC turnover.
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Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 42 (2015): 7983–7991, doi:10.1002/2015GL065595.
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Geophysical Research Letters 42 (2015): 7983–7991
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