Surface Water Mercury Concentrations in South San Francisco Bay, 2022-2024 Derived from Sentinel-2 Imagery

Mercury is a prevalent pollutant and neurotoxin in south San Francisco Bay that forms strong associations with suspended sediments and dissolved organics. Changes in surface water mercury levels have implications for water quality and scale via bioaccumulation to toxicity on higher trophic levels. This dataset includes GeoTIFF raster maps of estimations of surface water mercury concentrations in south San Francisco Bay between August 2022 and September 2024. Maps are of whole water total mercury (wwTHg, ng/L) and whole water methylmercury (wwMeHg, ng/L). The study area encompasses the region of San Francisco Bay, California, USA from the southern shore to approximately the Hayward-San Mateo Bridge as the northern bound. Each GeoTIFF file is a raster map of one mercury species (either wwTHg or wwMeHg) on a single day. The naming convention for all raster files is YYYYMMDD_wwTYPE, where YYYY is the year, MM is month, DD is the day, and TYPE is either wwTHg or wwMeHg. These raster maps were derived from 10m Sentinel-2 Muti-Spectral Imager (MSI) imagery (https://scihub.copernicus.eu/dhus/#/home) and atmospherically corrected in ACOLITE (https://github.com/acolite/acolite). Concentrations of Total Suspended Solids (TSS) and colored dissolved organic matter (CDOM) absorption at 440nm (a440) were retrieved based on water color reflectance in each pixel. We used discrete in-water data on TSS, a440, and mercury concentrations to empirically constrain biochemical relationships for the study area. TSS and a440 retrievals – along with instantaneous in situ temperature and specific conductivity measurements from a USGS continuous monitoring station – were then used to create the final mercury maps in this dataset. Mercury concentrations were reasonably well correlated with observations (wwTHg R² = 0.484, wwMeHg R² = 0.737) when evaluated against discrete data.