USING FOSSIL POLLEN TO TRACK VEGETATION & LAND USE CHANGES IN A 1500-YEAR TIDAL MARSH CORE

We present palynological data from sediment core B1A, collected in August 2023 from a tidal marsh in the Patuxent River watershed near Benedict, MD to supplement previous sedimentological, geochemical, and chronological analyses by reconstructing past vegetation, climate, and land use. The 3m core spans approximately the past 1500 years, from ~474 CE to 2023 CE, and contains four lithofacies that indicate variations in environmental setting over time. Stratigraphically, these include a basal marsh unit 4, transitional unit 3, estuarine unit 2, and uppermost marsh unit 1. We collected 1-cm thick samples approximately every 10 cm along the core and processed them using standard palynological methods (HCl, HF, acetolysis, KOH, and sieving). Tablets with known numbers of exotic palynomorphs were added for calculation of absolute pollen concentrations. Pollen analysis indicates significant changes in the composition of marsh vegetation at the site over the last 1500 years. Basal unit 4 was dominated by Cyperaceae (sedge) pollen. In the overlying transitional and estuarine units, marsh pollen was rare, and Quercus (oak) and Pinus (pine) pollen dominated the assemblages. The onset of Colonial land clearance (~1700 CE) is indicated by abundant Ambrosia (ragweed) pollen in Unit 1, followed by establishment of Amaranthaceae (pigweed)-dominated marshes. This research broadens our understanding of marsh change and response to human-activity, related land use, and climate fluctuations.