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).

克利尔湖（Clear Lake）坐落于加利福尼亚州中央谷西侧的海岸山脉范围内，是该州境内完全位于本州的最大天然淡水湖。该湖分为三个湖湾：西北部为广阔敞水区（上湖湾，Upper Arm），东南部为面积更小、更狭窄的区域（下湖湾，Lower Arm），东部则是最小且最狭窄的区域（奥克斯湖湾，Oaks Arm）。克利尔湖的水质因汞污染与有害藻华（Harmful Algal Blooms, HABs）而退化。其汞污染主要与硫河汞矿（Sulfur Bank Mercury Mine, SBMM）相关，该场地是自1992年起由美国环境保护署（U.S. Environmental Protection Agency, USEPA）管理的超级基金（Superfund）场址，坐落于奥克斯湖湾的东端。SBMM带来的汞污染及其在湖内的生物地球化学汞循环，正是美国地质调查局（U.S. Geological Survey, USGS）与美国环境保护署合作开展的研究核心主题。目前正开展监测与建模工作，以加深对营养盐动态如何影响汞（Hg）的循环、迁移与生物富集过程的理解。本次数据发布涵盖加利福尼亚州克利尔湖的有机质浓度与特征相关测量数据。本次发布的数据文件包含吸光度（Clear_Lake_Full_Spectra_Absorbance_Data.csv）与荧光（Clear_Lake_Vectorized_Fluorescence_Data.csv）分析的完整光谱结果，以及用于代理指标开发统计建模的荧光指数与矩阵计算结果（Clear_Lake_Sample_Summary.csv）。这些光谱中包含的常规诊断吸光度波长、荧光激发-发射对，以及一组常规计算得到的指数，已被上传至美国地质调查局国家水信息系统（National Water Information System, NWIS）数据库。本次发布的光学测量数据，旨在构建汞（Hg）与甲基汞（methylmercury, MeHg）浓度的额外潜在替代指标，并为解析湖内有机质的时空分布模式提供更完整的光谱信息。本次数据发布中包含的样本的其他水质数据，已发表于Marvin-DiPasquale等人（2020）与Agee等人（2024）的研究成果中。