Laboratory-based optical measurements for water samples collected from Clear Lake, California

Clear Lake, located within the Coast Range west of California's Central Valley, is the largest natural freshwater lake contained fully within the state. The lake has three arms: a large open-water region to the northwest (Upper Arm), a smaller and narrower region to the southeast (Lower Arm), and the smallest and narrowest region to the east (Oaks Arm). Water quality in Clear Lake is degraded by both by mercury contamination and harmful algal blooms (HABs). The mercury contamination is largely associated with the Sulfur Bank Mercury Mine (SBMM), a Superfund site managed by the U.S. Environmental Protection Agency (USEPA) since 1992 located on the eastern end of the Oaks Arm. Mercury contamination from SBMM and its biogeochemical mercury cycling within the lake are the focus of research being conducted by the U.S. Geological Survey (USGS) in cooperation with USEPA. Monitoring and modeling efforts are being implemented to improve understanding of the ways that nutrient dynamics affect the cycling, transport, and bioaccumulation of Hg. This data release documents measurements related to organic matter concentrations and characteristics in Clear Lake, California. Data files reported here provide full spectral results for absorbance (Clear_Lake_Full_Spectra_Absorbance_Data.csv) and fluorescence (Clear_Lake_Vectorized_Fluorescence_Data.csv) analyses as well as calculated fluorescence indices and arrays (Clear_Lake_Sample_Summary.csv) used for statistical modeling for proxy development. Commonly reported diagnostic absorbance wavelengths and fluorescence excitation-emission pairs contained in these spectra as well as a set of commonly calculated indices have been released to the USGS National Water Information System (NWIS) database. The optical measurements reported here were collected to establish additional potential surrogates for mercury (Hg) and methylmercury (MeHg) concentrations and to provide more complete spectral information on temporal and spatial patterns of organic matter within the lake. Other water-quality data for the samples included in this data release are published in Marvin-DiPasquale and others (2020) and Agee and others (2024).

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  "010:12"
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  "geospatial"
]