Date of Award

2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Doyle, Thomas W. & Reyes, Manuel R.

Abstract

Global climate change is a major environmental threat to natural and cultural resources in low-lying coastal zones and deltas worldwide. It is expected to have a significant effect on the development of coastal wetlands by changing species range expansion. In fact, recent studies have shown that there has been an increasing mangrove encroachment poleward in the Southern and Northern Hemispheres into temperate saltmarsh zones due to the lack of freeze events. This phenomenon could have a critical impact on the structure and function of tidal wetlands at critical latitudes, especially in carbon sequestration, since mangroves are thought to sequester more carbon than marshes due to their extensive roots, leaves, and branches. To understand this likely outcome of climate warming better, a study site was established in Port Fourchon, Louisiana, where mangroves are expanding into formerly saltmarsh-dominated habitat. The aim of this study was to estimate the rate and process of the conversion of marsh to mangrove and associated carbon sequestration of soils of historically saltmarsh or mangrove dominated cover in this locale. A chronosequence approach was used to compare carbon stores between mangrove and saltmarsh at different states of mangrove cover. Moreover, greenhouse experiments were conducted to understand the effects of different biotic properties and abiotic factors on propagule regeneration success and seedling growth. Results showed that tall Avicennia have higher aboveground biomass than Spartina and mixed mangrove/marsh zone. Tall Avicennia by habitat type also contributed the greater carbon storage and elevation compared to Spartina over the past 50 years based on 137Cs dating method. Propagule size, floating time, and temperature thresholds had significant effects on mangrove regeneration, while elevated CO2 and sunlight had no effect on propagule regeneration success.

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