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Sediment bulk density is the total mass of mineral and organic sediment within a defined volume. It is a key variable in many research questions pertaining to Bay sediment studies but one that is often poorly quantified and can be misinterpreted. The motivation for this report comes from a recommendation by Schoellhamer et al. (2018) to compile more accurate estimates of bulk density of Bay sediments to convert between volume and mass with a higher level of certainty. Through funding and guidance from the Bay Regional Monitoring Program Sediment Work Group, this report is a first step towards compiling the available data on sediment bulk densities across Bay habitats and along salinity gradients to provide better information for resource managers and others working on sediment-related issues. This report discusses the need to know the bulk density of Bay soils to convert between sediment mass and soil volume; clarifies general definitions and common points of confusion related to sediment bulk density; compiles primary sources of bulk density measurements, secondary sources of bulk density estimates, and standard engineering estimates of bulk density for different habitats in San Francisco Bay; and, provides a database where practitioners can track, analyze, and share bulk density measurements.
 

This report proposes a multi-faceted redesign of the South San Francisco Bay shoreline at the interface with Calabazas and San Tomas Aquino creeks. Recognizing the opportunities presented by changing land use and new challenges, such as accelerated sea-level rise, we explore in this report a reconfigured shoreline that could improve ecosystem health and resilience, reduce maintenance costs, and protect surrounding infrastructure.

Sediment is a lifeblood of San Francisco Bay (Bay). It serves three key functions: (1) create and maintain tidal marshes and mudflats, (2) transport nutrients and contaminants, and (3) reduce impacts from excessive human-derived nutrients in the Bay. Because of these important roles, we need a detailed understanding of sediment processes in the Bay.

This report offers a conceptual understanding of how fine-grained sediment (i.e. silt and finer, henceforth called fine sediment) moves around at different scales within the Bay, now and into the future, to synthesize current knowledge and identify critical knowledge gaps. This information can be used to support Bay sediment management efforts and help prioritize funding for research and monitoring. In particular, this conceptual understanding is designed to inform future San Francisco Bay Regional Monitoring Program (RMP) work under the guidance of the Sediment Workgroup of the RMP for Water Quality in San Francisco Bay, which brings together experts who have worked on many different components of the landscape, including watersheds and tributaries, marshes and mudflats, beaches, and the open Bay. This report describes sediment at two scales: a conceptual understanding of open-Bay sediment processes at the Bay and subembayment scale (Chapter 2); and a conceptual understanding of sediment processes at the baylands scale (Chapter 3). Chapter 4 summarizes the key knowledge gaps and provides recommendations for future studies.

Microplastic particles (MPs) are ubiquitous across a wide range of aquatic habitats but determining an appropriate level of risk management is hindered by a poor understanding of environmental risk. Here, we introduce a risk management framework for aquatic ecosystems that identifies four critical management thresholds, ranging from low regulatory concern to the highest level of concern where pollution control measures could be introduced to mitigate environmental emissions. The four thresholds were derived using a species sensitivity distribution (SSD) approach and the best available data from the peer-reviewed literature. This included a total of 290 data points extracted from 21 peer-reviewed microplastic toxicity studies meeting a minimal set of pre-defined quality criteria. The meta-analysis resulted in the development of critical thresholds for two effects mechanisms: food dilution with thresholds ranging from ~ 0.5 to 35 particles/L, and tissue translocation with thresholds ranging from ~ 60 to 4100 particles/L. This project was completed within an expert working group, which assigned high confidence to the management framework and associated analytical approach for developing thresholds, and very low to high confidence in the numerical thresholds. Consequently, several research recommendations are presented, which would strengthen confidence in quantifying threshold values for use in risk assessment and management. These recommendations include a need for high quality toxicity tests, and for an improved understanding of the mechanisms of action to better establish links to ecologically relevant adverse effects.