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.

Coastal wetlands are considered one of the most productive natural ecological infrastructures in the world. Although coastal ecosystems total only 6% of global surface area, they provide an estimated 38% of global ecosystem services. Despite their environmental and societal value, coastlines and coastal habitats are increasingly threatened by human activity. Human threats include proximal disruptions such as wetland removal, changes in sedimentation and chemical pollution. Additionally, climate change, and more specifically sea-level rise (SLR) poses one of the greatest global threats to coastal marshes. Estimates for future SLR rates range anywhere from 0.3 m to over 1.3 m by the end of the 21st century. While historical observations have shown that tidal wetlands can tolerate and dynamically adjust in elevation to some rate of SLR, there are limits. Human population growth, coastal development and the concept of coastal squeeze constrain landward vertical migration of marshes and bring in additional factors that challenge efforts to understand and manage future salt marsh trajectories. Indeed, humans are integrated into the very fabric of major processes governing wetland stability, which can have major impacts on ecogeomorphic feedback systems and overall marsh resiliency. Thus, local anthropogenic stressors should be coupled with climate change impacts in management and conservation efforts, as they often interact synergistically. However, to do so effectively requires communication and unified actions by stakeholders, managers, and scientists. In the following dissertation, I plan to tie these themes together by researching the multiple human and climatic stressors on California coastal marshes and creating knowledge that can be used in science-policy settings. Furthermore, I use a participant-observer approach to study the communication and planning for mitigating coastal threats in California. First, I obtain high-resolution geochemical data from three coastal marshes in the San Francisco Bay to look at responses to recent anthropogenic changes in sedimentation and pollutant loadings in the context of marsh conditions and histories since the mid-Holocene. Next, I look at attempts to mitigate the impacts of SLR through a large-scale sediment addition project in Seal Beach National Wildlife Refuge, CA. I use the analysis of sediment cores, to understand natural accretion and variability over time and how it compares to the artificial accretion and sedimentation from sediment addition. Lastly, I utilize information from a longer-term participant-observer project updated and augmented with my own participant-observer experience with the SWCASC funded coastal workshops to provide an analysis on knowledge co-production efforts in coastal management settings to understand what makes knowledge relevant in management and policy contexts.