SUB-SEASONAL INTERTIDAL SEDIMENTATION IN A SOUTHERN CALIFORNIA ESTUARY

Estuaries in Southern California are particularly vulnerable to sea level rise as they are constrained by urbanization and/or steep topography which limits upland habitat migration. Therefore, estuarine habitat resilience and sustainability in the region are primarily dependent on building elevation capital through increases in sedimentation. To address this issue, resource managers in California are increasingly interested in better understanding sedimentation in the region and pursuing interventions to minimize shoreline erosion and promote sediment deposition. In this project, we leverage an ongoing monitoring of a Living Shorelines restoration project to quantify and characterize seasonal sedimentation in Newport Bay, Newport Beach, California. Sedimentation at these sites was monitored for two years, with measurements including bimonthly sediment deposition using sediment tiles and sediment characterization via grain size, total organic matter, and percent organic carbon and nitrogen. Our results reveal that sedimentation was generally higher in the summer and lower in the winter months. This is unexpected, as the majority of Southern California’s precipitation (and runoff) occurs during winter months, suggesting sediment supply to this section of the estuary is likely driven by non-fluvial sources. Additionally, these results suggest that Living Shorelines restoration projects may be more effective at promoting upshore sedimentation within the estuary than unmodified shoreline. Further analyses of sediment composition demonstrate temporal variability in sediment characteristics such as grain size and organic matter. This study allows us to better understand the timing and type of sediment delivery to these systems and the impact of shoreline management interventions on sedimentation. Collectively, these outcomes may assist with shoreline management to combat sea level rise in estuaries in the region.