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High-resolution geochemical record of three marshes from the San Francisco Bay area

Authors: Elizabeth Fard*, UCLA Institute for the Environment, Lauren Brown, UCLA, Scott Lydon, UCLA, Glen MacDonald, UCLA
Topics: Paleoenvironmental Change, Coastal and Marine, Physical Geography
Keywords: heavy metals, coastal salt marshes, estuaries, high-resolution stratigraphy
Session Type: Paper
Presentation File: No File Uploaded

The San Francisco Bay has the largest concentration of salt marshes in the state of California, representing a diversity of marsh habit. Protecting these environments is critical, as salt marshes provide refuge to endangered species, absorb carbon from the atmosphere, and preserve detailed evidence of past climatic, hydrologic, geomorphic, and ecologic conditions. In the last 170 years, 95% of the historic tidal wetlands in the bay have been destroyed due to diking and filling. Additionally, many of the remaining marshes have been impacted by pollutants such as heavy metals over this period, making ecological trajectories and resilience to disturbance uncertain. In this study, we collected data from three different marshes in the Bay Area to document the geochemical changes including heavy metal concentrations, and shifts in productivity as a response to climatic and anthropogenic changes since the mid-Holocene. Preliminary results confirm anthropogenic impacts on the geochemistry of marshes in the San Francisco Bay over the last 150-200 years following European arrival. However, based on statistical time-series analysis of long-core elemental concentrations, results show that modern conditions are not so far removed compared to prehistoric conditions, as often suggested by century-scale analyses. Modern levels of Pb and Mn are unprecedented throughout the cores, likely due to increased erosion due to European land clearance, logging, and increased production and emissions of Pb (lead). Our results show the effects of anthropogenic changes on these ancient and ecologically important marshes that can help better inform restoration ecologists and policymakers.

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