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High-resolution geochemical record of Petaluma Marsh from the San Francisco bay area

  • Author(s): Fard, Elizabeth
  • Advisor(s): MacDonald, Glen M.
  • et al.
Abstract

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. However, much of the marshes have been impacted by pollutants, altered or lost entirely due to human activity over the past 150 years, making their prehistoric conditions, ecological trajectories and resilience to disturbance uncertain. In this study, I collected data from Petaluma Marsh, one of the oldest marshes in the Bay Area, to document the geochemical changes including heavy metal concentrations as a response to climatic and anthropogenic changes since the mid-Holocene. Loss-on ignition, pXRF, and magnetic susceptibility data were collected at high resolution from a 12-meter, 6109-year-old, sedimentary core recovered from this tidal marsh located along the Petaluma river in the northern Bay region. Average rate of sediment accretion is 3.6 mm yr-1 � 0.8. Our results show that the introduction of European land-use and activities over the last 150-200 years resulted in disturbance of marsh biota and increases in heavy metals with unprecedented levels of lead and zinc. However, based on statistical time-series analysis of long-core elemental concentrations, results show that modern geochemical conditions are not so far removed compared to prehistoric conditions, as often suggested by century-scale analyses. Modern heavy metal concentrations (e.g., Cr, Fe, Sr, Ba, Zr, Rb and Ni) match concentration levels from 4000-6000 YBP. However, Pb levels in the marsh post-European land use are dramatically higher now than ever before. Our results show the effects of anthropogenic changes on this ancient and ecologically important marsh in the north San Francisco Bay area that can help better inform restoration ecologists and policy makers, specifically in terms of heavy-metal pollutants.

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