Mercury is a neurotoxin and environmental pollutant that endangers the health of humans and wildlife. When mercury flows into aquatic environments like San Francisco Bay (SFB), it can be converted by microorganisms to methylmercury (MeHg), which is the most poisonous of mercury compounds. MeHg bioaccumulates in aquatic food webs and can cause a wide range of impairments in fish, birds, and humans. Little is known about mercury concentrations at the margins of SFB and how climate change, including changes in temperature and precipitation, will affect mercury exposure and methylmercury production. In addition, the San Francisco South Bay Salt Ponds Restoration Program (SBSPRP) needs more efficient and effective monitoring of mercury changes at regional spatial scales. The goal of this new project is to map total mercury (THg) and MeHg in South SFB through satellite remote sensing (Sentinel-2) of two known mercury indicators, total suspended solids (TSS) and colored dissolved organic matter (CDOM), with quantified accuracy. The research aims to improve understanding of regional mercury spatial and temporal trends associated with weather events and wetland restoration management activities and improve mercury monitoring efficiencies. One main project objective is to assess the capacity to detect anomalies in remotely sensed TSS, CDOM, and mercury species associated with recent weather events or restoration activities through time series analysis. Researchers will also coordinate with the SBSPRP Project Management Team to develop remote sensing products that communicate patterns in mercury and their uncertainties to a broad range of resource managers, decision makers, and the public.
This project, which represents a collaboration between the U.S. Geological Survey (USGS) Western Geographic Science Center, USGS Water Mission Area, and the USGS California Water Science Center (CAWSC), was successfully launched in August 2022 with the first boat survey of the margins and deeper water environments of South SFB. The project will use the surveys to generate a robust multi-variable, in-water dataset coupled with near-field radiometric measurements. These field measurements will be used to develop models that relate remotely sensed TSS and CDOM to in situ mercury concentrations, which will allow for the development of mercury, TSS, and CDOM maps with quantified uncertainty. Data collection is enhanced by CAWSC collaborative work with the San Francisco Estuary Institute Nutrient Management Strategy (NMS). To support the NMS, CAWSC team members are leading high-resolution continuous mapping surveys of water quality across South SFB to characterize and compare biogeochemical processes occurring on the shoals and within channel and deeper water environments. These datasets will provide opportunities to further understand relationships between environmental setting and mercury speciation.
Scientists collecting surface water radiometric data using a Seabird Scientific Hyperspectral Surface Acquisition System (HyperSAS). Photo credit: Ayelet Delascagigas (U.S. Geological Survey).
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