Degree

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

Document Type

Dissertation

Abstract

Coastal deltaic floodplain development occurs when riverine sediment delivery to coastal margins facilitates land accretion at a rate that exceeds the combined effect of eustatic sea level rise and geologic subsidence, leading to an actively prograding deltaic landscape. In a coastal setting environmental conditions are driven by river discharge, winds, tides and vegetation. The combination of these physical and biological forces over time creates a spatial heterogeneity in the landscape, which determines patterns of ecological succession. These successional changes are recorded in the soils and sediments of the delta and occur along age and elevation gradients. I described spatial and temporal patterns in soil development, sediment architecture and carbon (C) burial in a young emergent coastal floodplain, the Wax Lake Delta (WLD).

I selected a series of conceptual models with which to develop hypotheses on expected patterns in delta development such as the Walker and Syers (1976) soil development conceptual model. I found increasing organic material and decreasing mineral inputs over time demonstrating an increase in vegetative influence on soil development that was also reflected in the delta geologic record. Facies classified by depositional environment (modified from van Heerden and others 1981) a transition from a dominance of hydro-geophysical forcings on delta development to biological dominance as the delta matures. There was a switch from thicker marsh deposits in the older, higher elevation wetlands near the delta apex to thicker prodelta deposits at the delta edge and expanding delta front. Spatial patterns in facies thickness and C stocks led me to conclude that delta marsh deposits, future peat, should not be the sole focus of deltaic C burial studies. There were surprising similarities in C stock among all facies depositional environments along the subaerial delta emergence gradient demonstrating the importance of analyzing all of the delta deposits for C storage estimates. I found 1.45 Tg C buried in WLD, which was more than three times the Shields and others (2017) estimate. I also estimated that there is 1.73 Tg of C buried in the subaqueous delta front, more than doubling the estimated C storage in WLD to 3.18 Tg C.

Date

3-18-2019

Committee Chair

Twilley, Robert

Available for download on Wednesday, March 17, 2021

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