A Late-Holocene Pollen Record of Coastal Ecosystem Changes and Mangrove Development in Louisiana

Authors: Junghyung Ryu*, Department of Oceanography and Coastal Sciences, College of the Coast and Environment, Louisiana State University, Kam-biu Liu, Department of Oceanography and Coastal Sciences, College of the Coast and Environment, Louisiana State University, Terrence A. McCloskey, Cherokee Nation Technology Solutions, Contracted to U.S. Geological Survey Wetland and Aquatic Research Center, Parker Coliseum, Baton Rouge, Louisiana, 70803, United States
Topics: Environmental Science, Biogeography, Coastal and Marine
Keywords: Louisiana, Mangrove, Wetland, Pollen, Climate, Sea level, Geochemistry.
Session Type: Paper
Day: 4/3/2019
Start / End Time: 9:55 AM / 11:35 AM
Room: Taylor, Marriott, Mezzanine Level
Presentation File: No File Uploaded

Significant biogeographic events such as the poleward expansion of black mangrove (Avicennia germinans) due to increasing temperature is linked with global climate change. Previous studies have documented the recent expansion of A. germinans populations along the Gulf of Mexico. However, the lack of millennial-scale paleoenvironmental records in Louisiana’s wetlands has hindered the forecasting of black mangrove’s future range expansion. This paper reports on a palynology-based multi-proxy analysis of a 3.72 m sediment core retrieved from a small pond on a mangrove-dominated island behind Bay Champagne near Port Fourchon, LA. The study area has experienced very rapid shoreline retreat that has dramatically shortened the distance from the coring site to the sea during the past century, resulting in the replacement of a Juncus-Spartina marsh by a dense A. germinans community. The pollen record shows three stages of ecological changes from a Taxodium-Nyssa freshwater forest (3.5-1.0 cal yr BP) with elevated concentrations of Fe and Ti, to a Typha-Sagittaria intermediate marsh (1.0-0.4 cal yr BP), and to a Spartina-dominated saline marsh (since 0.4 cal yr BP) with an increase in Sr and Cl concentrations. A. germinans has been present since the 20th century. Significant increases in the concentrations of Sr and in the Cl/Br ratio towards the core top are possibly related to relative sea level rise and extreme events like hurricanes. Our findings suggest that the expansion of A. germinans in the Port Fourchon area is related to climate warming, relative sea level rise, and shoreline retreat during the past century.

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