Murray State Theses and Dissertations

Abstract

Floodplains can store large amounts of soil organic carbon (SOC) despite covering a small fraction of the global land area. Since these valley-bottom landforms build through the action of flooding, the century to millennial-scale record of overbank deposition could be important in understanding controls on deep (>30 cm) SOC storage. Yet, the influence of flood history and landform development on carbon content is surprisingly not well known. I use a combined geological and pedological approach to characterize the sedimentation, soil development, and SOC of fluvial terraces along an impounded reach of the humid-subtropical Tennessee River valley, U.S.A. The standardized >0.25 mm sand fraction from both relict levee and floodplain alluvial soil profiles record a Late Holocene paleoflood history where inferred paleo-magnitude increased after 2000 yr BP coincident with increased paleohurricane activity from the Caribbean to the Gulf Coast. This valley-wide increase in flood magnitude coincides with a decrease in deep SOC content. However, this deep SOC also varies by landform type. Fine-grained floodplains store more SOC than the coarse-grained levee. However, the buried SOC content of the latter is more reliant on clay and silt, which is an important supply limit in a conceptual model of fluvial landform development. That is, in silt- and clay-limited fluvial landforms (e.g., levees), changes in the amount of fine sediment added during flooding will have a more direct effect on the SOC content by means of aggregate formation and clay film development. In contrast, variations in flood magnitude will have little to no effect on the SOC content of fine-grained landforms (e.g., flood basin) as lower flood energy contributes to deposition of detrital organic matter and silt and clay act which act to protect SOC through elluviation-illuviation and aggregate formation. This study emphasizes that parent material layering from flooding and the subsequent translocation of fine particles down profile are interdependent processes that can influence the storage of SOC on longer timescales (>102 yr). Conservation measures should consider how natural flooding affects landform development and the SOC storage in floodplains.

Year manuscript completed

2020

Year degree awarded

2020

Author's Keywords

Paleoflood, SOC, floodplains, soil carbon, Tennessee River, Paleosol

Thesis Advisor

Gary E. Stinchcomb

Committee Chair

Gary E. Stinchcomb

Committee Member

Bassil El Masri

Committee Member

Michael B. Flinn

Committee Member

Howard Whiteman

Document Type

Thesis

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