Optical measurements for surface water samples collected within South San Francisco Bay in support of mercury modeling

Little is known about mercury concentrations at bay margins, and how climate change, including changes in temperature and precipitation, will affect mercury exposure and methylmercury (MeHg) production. In addition, the San Francisco South Bay Salt Ponds Restoration Program (SBSPRP) needs more efficient and effective mercury monitoring approaches at larger spatial scales to understand changes in mercury at a regional level. The goal of this new project, a collaboration between the USGS Western Geographic Science Center, Water Mission Area, and the California Water Science Center (CAWSC), is to develop the capacity to map total mercury (THg) and MeHg in South San Francisco Bay (SFB) through the satellite remote sensing (Sentinel-2) of two known mercury indicators: total suspended solids (TSS) and colored dissolved organic matter (CDOM). In addition to quantifying the accuracy of this approach, this research aims in South SFB using the Sentinel-2 satellite in order to 1) improve understanding of region-wide mercury spatial and temporal trends associated with weather events and wetland restoration management activities, and 2) improve mercury monitoring efficiencies and capabilities moving forward. 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. The optical measurements reported here were collected to aid in the characterization of water sources and mixtures and establish proxies (surrogates) for mercury and methylmercury concentrations and to provide ground-truthing for remotely sensed models of dissolved organic carbon (DOC) concentrations. Data are compiled into five tables: 1) full fluorescence spectra in vectorized format (LSB_Hg_RS_EEMs_vectors.csv), 2) full absorbance spectra for 1 centimeter (cm) path measurements (LSB_Hg_RS_1cm_ABS_scans.csv), 3) full absorbance spectra for 10 cm path measurements (SSFB_Hg_RS_10cm_ABS_scans.csv), 4) absorption coefficients derived from the 10cm path measurements (SSFB_Hg_RS_10cm_ag_scans.csv), and 5) summary file of commonly extracted optical indicators and calculated wavelength-array values derived from the optical data that correspond to arrays measured by field-based sensors for use in statistical analyses and model development (LSB_Hg_RS_OMRL_Sample_Summary.csv).