Degree

Doctor of Oceanography and Coastal Sciences (POCS)

Department

Oceanography and Coastal Sciences

Document Type

Dissertation

Abstract

The objective of this dissertation is to develop millennial-scale paleoenvironmental reconstructions in Louisiana’s coastal wetlands and to investigate the various mechanisms that affected the Holocene development of swamp forests and marshes along a salinity gradient by conducting a palynology-based, multi-proxy investigation. This study will fill an important knowledge gap regarding ecosystem response to natural and anthropogenic impacts, which will help our wetland restoration efforts in the near future.

This dissertation will address the following research questions: (a) What are the major mechanisms of wetland formation in coastal Louisiana? (b) Can we distinguish the relative importance of natural vs. anthropogenic factors in wetland development? (c) What are the histories of Louisiana’s wetland evolution in response to external forcing (e.g., delta-lobe switching)? (d) How did the vegetation respond to sea level/climate changes during the late Holocene?

Long-sediment cores (>5 m) were collected from four wetlands along a salinity gradient (i.e., cypress swamp, fresh marsh, intermediate, and mangrove swamp). These cores were analyzed using palynological, sedimentological (loss-on-ignition and laser grain-size analyses), geochemical (X-ray fluorescence), and radiometric (C-14, Cs-137, and Pb-210) dating techniques.

Although the detailed histories of ecological changes vary spatially and temporally at different ecosystems in conjunction with the Mississippi delta’s evolution, ecosystem succession followed a general sequence from a shell-rich bay/interdistributary coastal environment, to a fluvially-dominated swamp/marsh during delta progradation, to an intermediate/brackish marsh, and finally to salt marsh or mangroves or open water during delta abandonment and marine transgression. Our findings suggest that ecosystem succession was highly associated with the Mississippi delta cycle.

Important non-climatic controls are dominant in cypress swamp and fresh-intermediate marshes, such as the lobe-switching and fluvial processes. Salt marshes and mangrove swamps along the coast are controlled by relative sea-level rise and hurricanes. Anthropogenic activities have had significant impacts on the freshwater swamps and marshes, including commercial logging and canal dredging.

This study provides a detailed history of wetland evolution in coastal Louisiana in conjunction with the ecological, hydrological, and geological changes and anthropogenic impacts during the late Holocene. This new knowledge, and the long-term perspectives it provides, can contribute to the development of sound policy and practices for wetland protection and restoration projects.

Date

8-14-2020

Committee Chair

Liu, Kam-biu

Available for download on Monday, August 09, 2027

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