Data in this data release were obtained for water samples collected under Yellowstone National Park Research Permit YELL-05194 in 2017 through the Integrated Yellowstone Studies Project funded by the Mineral Resources Program. Isotope-spiked incubations were carried out to determine methylation and demethylation potential for Frying Pan spring, Crystal Sister East, Crystal Sister West, and Turbulent Pool, which were selected based on existing data on total mercury and methylmercury concentrations (see companion data release (https://doi.org/10.5066/P9IUY03O). The data represent the experimental conditions of incubation experiments (temperature, time, and experimental spikes) and concentration data associated with each condition.

Data in this data release were obtained from water samples collected under Yellowstone National Park (YNP) Research Permit YELL-05194 in 2017, 2019, and 2020 through the Integrated Yellowstone Studies Project funded by the Mineral Resources Program. These samples were used to assess mercury cycling within YNP. Water samples were analyzed for total mercury and methylmercury, the bioaccumulated form in food webs. This data informs the biogeochemical processes controlling the broad range of mercury and methylmercury concentrations observed in the park. Natural abundance mercury stable isotopes were also collected to determine if mercury sources or cycling processes varied between different hydrothermal sources. Data produced as part of this study outlines how the different physicochemical processes, including mixing between meteoric and hydrothermal waters, boiling, and sorption, affect mercury isotope values in YNP.

This dataset includes the field measurements and laboratory analyses of surface water, seston, and sediment collected from Lake Powell, within Glen Canyon National Recreation area (GLCA), during high flow (May-June 2014) and low flow (August 2015) conditions. The study area includes 12-13 sampling sites that follow a transect spanning the entire length of the reservoir from the Colorado River inflow to the Glen Canyon dam, as well as the San Juan River arm, the Escalante River arm and West Canyon. Bed sediment samples were analyzed for mercury speciation, methylmercury production and degradation rates, total reduced sulfur, iron speciation, organic content, and 16S rRNA gene templates as a proxy for microbial abundances. Water samples were collected from 3-5 depths at each site and analyzed for: total mercury (filtered and particulate), methylmercury (filtered and particulate), dissolved organic and inorganic carbon with 13C isotopic ratios, nutrients, anions, cations, trace metals, particulate carbon (with 13C isotopic ratios) and particulate nitrogen (with 15N isotopic ratios). Water quality sonde (EXO) field measurements included specific conductivity, temperature, pH, dissolved oxygen, fluorescent dissolved organic matter, chlorophyll, and turbidity. Fish samples were also collected during November 2014 from Good Hope Bay (upper reservoir), Wahweap Bay (lower reservoir), and the San Juan arm and assayed for total mercury for comparison with previous striped bass samples collected by the state of Utah. There are nine files (*.csv) in this dataset: 1) data dictionary ; 2) sediment data; 3) water data; 4) seston data; 5) fish data; 6) EXO main channel profile data ; 7) EXO off channel profile data; 8) quality assurance data; and 9) molecular data.

There are over 10,000 hydrothermal features in Yellowstone National Park (YNP), where waters have pH values ranging from about 1 to 10 and surface temperatures up to 95 °C. Active hydrothermal areas in YNP provide insight into a variety of processes occurring at depth, such as water-rock and oxidation-reduction (redox) reactions, the formation of alteration minerals, and microbial (thermophile) metabolism in extreme environments, and possible indications of volcanic unrest. Investigations into the water chemistry of hydrothermal features, streams, and rivers in YNP have been conducted by the U.S. Geological Survey (USGS) and other earth-science organizations and academic institutions since 1883 (Gooch and Whitfield, 1888; Price and others, 2024). More recently, USGS researchers have sampled hydrothermal features in YNP at least annually since 1994 (McCleskey and others, 2014, and references within). In this Data Release, the chemical and isotopic analyses of 845 water samples collected beginning in 2009 are reported for numerous thermal and non-thermal features in YNP. This report combines water chemistry data presented in McCleskey and others (2014) with data collected after 2014. These water samples were collected and analyzed as part of research investigations in YNP on and as part of the Yellowstone Volcano Observatory monitoring plans (Yellowstone Volcano Observatory, 2006); arsenic, iron, nitrogen, and sulfur redox species in hot springs and overflow drainages; the occurrence and distribution of dissolved mercury and arsenic; and general hydrogeochemistry of hot springs throughout YNP. For most samples, data includes water temperature, pH, specific conductance, dissolved oxygen, and concentrations of major cations, anions, trace metals, alkalinity, sulfur redox species (hydrogen sulfide and thiosulfate), nutrients, silica, boron, arsenic and iron redox species, acidity, dissolved organic carbon, and hydrogen and oxygen isotope ratios. For select samples, tritium (3H), stable carbon isotopes of the dissolved inorganic carbon, and sulfur isotopes of sulfate are presented. In addition, chemical data for river, stream, and lake waters were obtained to determine input of different solutes from thermal areas throughout YNP. References Cited Gooch, F.A., and Whitfield, J.E., 1888, Analyses of waters of the Yellowstone National Park with an account of the methods of analysis employed: Bulletin 47, p. 84. McCleskey, R.B., Chiu, R.B., Nordstrom, D.K., Campbell, K.M., Roth, D.A., Ball, J.W., and Plowman, T.I., 2014, Water-Chemistry Data for Selected Springs, Geysers, and Streams in Yellowstone National Park, Wyoming, Beginning 2009: doi:10.5066/F7M043FS. Price, M.B., McCleskey, R.B., Oaks, A., Hurwitz, S., and Nordstrom, D.K., 2024, Historic Water Chemistry Data for Thermal Features, Streams, and Rivers in the Yellowstone National Park Area, 1883-2021: U.S. Geological Survey data release, https://doi.org/10.5066/P9KSEVI1. Yellowstone Volcano Observatory, 2006, Volcano and earthquake monitoring plan for the Yellowstone Volcano Observatory, 2006-2015: U.S. Geological Survey Scientific Investigations Report 2006-5276, http://pubs.usgs.gov/sir/2006/5276/. First posted - September 19, 2022 (available from author) Revised - March 4, 2025 (version 2.0) NOTE: While previous versions are available from the author, all the records in previous versions can be found in version 2.0.

There are over 10,000 hydrothermal features in Yellowstone National Park (YNP), where waters have pH values ranging from about 1 to 10 and surface temperatures up to 95 °C. Active hydrothermal areas in YNP provide insight into a variety of processes occurring at depth, such as water-rock and oxidation-reduction (redox) reactions, the formation of alteration minerals, and microbial (thermophile) metabolism in extreme environments, and possible indications of volcanic unrest. Investigations into the water chemistry of hydrothermal features, streams, and rivers in YNP have been conducted by the U.S. Geological Survey (USGS) and other earth-science organizations and academic institutions since 1883 (Gooch and Whitfield, 1888; Price and others, 2024). More recently, USGS researchers have sampled hydrothermal features in YNP at least annually since 1994 (McCleskey and others, 2014, and references within). In this Data Release, the chemical and isotopic analyses of 845 water samples collected beginning in 2009 are reported for numerous thermal and non-thermal features in YNP. This report combines water chemistry data presented in McCleskey and others (2014) with data collected after 2014. These water samples were collected and analyzed as part of research investigations in YNP on and as part of the Yellowstone Volcano Observatory monitoring plans (Yellowstone Volcano Observatory, 2006); arsenic, iron, nitrogen, and sulfur redox species in hot springs and overflow drainages; the occurrence and distribution of dissolved mercury and arsenic; and general hydrogeochemistry of hot springs throughout YNP. For most samples, data includes water temperature, pH, specific conductance, dissolved oxygen, and concentrations of major cations, anions, trace metals, alkalinity, sulfur redox species (hydrogen sulfide and thiosulfate), nutrients, silica, boron, arsenic and iron redox species, acidity, dissolved organic carbon, and hydrogen and oxygen isotope ratios. For select samples, tritium (3H), stable carbon isotopes of the dissolved inorganic carbon, and sulfur isotopes of sulfate are presented. In addition, chemical data for river, stream, and lake waters were obtained to determine input of different solutes from thermal areas throughout YNP. References Cited Gooch, F.A., and Whitfield, J.E., 1888, Analyses of waters of the Yellowstone National Park with an account of the methods of analysis employed: Bulletin 47, p. 84. McCleskey, R.B., Chiu, R.B., Nordstrom, D.K., Campbell, K.M., Roth, D.A., Ball, J.W., and Plowman, T.I., 2014, Water-Chemistry Data for Selected Springs, Geysers, and Streams in Yellowstone National Park, Wyoming, Beginning 2009: doi:10.5066/F7M043FS. Price, M.B., McCleskey, R.B., Oaks, A., Hurwitz, S., and Nordstrom, D.K., 2024, Historic Water Chemistry Data for Thermal Features, Streams, and Rivers in the Yellowstone National Park Area, 1883-2021: U.S. Geological Survey data release, https://doi.org/10.5066/P9KSEVI1. Yellowstone Volcano Observatory, 2006, Volcano and earthquake monitoring plan for the Yellowstone Volcano Observatory, 2006-2015: U.S. Geological Survey Scientific Investigations Report 2006-5276, http://pubs.usgs.gov/sir/2006/5276/. First posted - September 19, 2022 (available from author) Revised - March 4, 2025 (version 2.0) NOTE: While previous versions are available from the author, all the records in previous versions can be found in version 2.0.

USGS conducted preliminary assays on aged (3 mo.) surface sediment (0-4 cm) collected from 13 sites during October 1998 in order to decipher general spatial trends in Hg-speciation, microbiology and relevant biogeochemistry. During the second field campaign sample processing and incubations were conducted at ambient temperature within hours of sediment collection to provide a more accurate measure of in-situ process rates and analyte concentrations. The third field sampling (October 1999), involving 14 sampling and was conducted with a similar approach as in June 1999. The latter two data sets provide a direct seasonal comparison (summer/fall, high/lo flow conditions) of Hg transformation dynamics in the CRS. Sediment depth profiles (0-16 cm) were investigated at four sites during June 1999 and at two of these four during October 1999. Eroding vertical bank material was sampled in the Hg-contaminated Fort Churchill region during both 1999 dates. Laboratory experiments were conducted using sediment collected during the latter two sampling dates. The study purpose sought to: a) identify important zones of net methylmercury (MeHg) production and consumption within the CRS, b) determine which environmental factors most strongly influence these processes and c) provide estimates of seasonal variability. Measurements were made of microbial Hg-transformations (via radiotracer) and in-situ Hg speciation (total mercury (Hgt), MeHg, and particle-associated acid-extractable Hg(II)). Acid extractable Hg(II) was used as a surrogate measure for the Hg(II) most readily available to bacteria for methylation. A novel Hg-biosensor technique was also used to assess bioavailable Hg(II) in pore-water. A suite of ancillary microbial processes and sediment geochemical parameters were also measured to more fully characterize each site, and to relate these measurements to observed Hg-transformation rates and Hg-speciation. The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues.

Degassing thermal features at Yellowstone National Park include spectacular geysers, roiling hot springs, bubbling mud pots, fumaroles, frying pans, and areas of passive degassing characterized by steaming ground. Most of these features are readily identified by visible clouds of steam that are occasionally accompanied by a strong “rotten egg” odor from emissions of hydrogen sulfide gas. Gas compositions typically are greater than 90% carbon dioxide with lesser amounts of helium, hydrogen, hydrogen sulfide, methane, nitrogen and other trace components. The composition of the gas and relative amounts of gas and steam relate both to the type of feature as well as the geographic location within the park. In 2003 we began a long-term field study of Yellowstone gases with a goal of obtaining complete chemical analyses from a variety of features from all areas of the park. Results from samples collected through 2012 are published in numerous journal articles and reports (Bergfeld et al., 2012, 2014; Chiodini et al., 2012; Evans et al., 2010; Lowenstern et al., 2012, 2014, 2015; and Werner et al., 2008). Synthesis of these data allow us to delineate areas within Yellowstone that are dominated by magmatic versus crustal gas sources and to tease out additional information regarding sedimentary and metamorphic sources for crustal gas. This report compiles our published gas and water data with new gas data from samples collected through September, 2018 and includes some previously unpublished carbon isotope data from waters collected during 2011. Some of the analyses represent replicate samples collected in different bottles on the same day, others are samples collected from the same location in different years, and some sites were only sampled once. A companion data release focused on water chemistry and discharge for 2017-18 waters is planned be published in a separate report. The data herein are organized by sample type: Tables 1 and 2 include bulk chemistry and isotope data for 199 gas samples collected in evacuated bottles containing sodium hydroxide and 41 gas samples collected in dry evacuated bottles, respectively; Table 3 presents chemical and isotope data for 62 water samples from thermal and non-thermal features; Table 4 contains helium and carbon isotope data for 10 water samples and 1 gas sample. Each sample is assigned a group number linked to a particular area within the park (figure 1). Samples in groups 2 through 10 and 12 through 22 tend to be in close proximity. Group 11 includes samples from general locations across Eastern Yellowstone. Samples keyed to group 1 (miscellaneous) are not co-located. The analytical results include major and trace element chemistry for the gases and waters, and isotope values for carbon dioxide (d13C-CO2), dissolved inorganic carbon (d13C-DIC), helium (3He/4He), steam (d18O, dD), neon (20Ne/22Ne and 21Ne/22Ne), and argon (38Ar/36Ar and 40Ar/36Ar). All data in this report supersede previously published analyses. The reader is directed to early publications for details on sampling and analytical methods and for in depth discussions regarding interpretations of the gas data.

Water analyses are reported for 66 samples collected from numerous thermal and non-thermal (rivers and streams) features in the southwestern areas of Yellowstone National Park (YNP) during 2009, 2017, and 2018. Water samples were collected from sources near Boundary Creek, Bechler River, Falls River, Mountain Ash Creek, Upper Snake River, Spirea Creek, and Lewis Lake. These water samples were collected and analyzed as part of research investigations on the chemistry of Yellowstone’s hydrothermal system and on the distribution of dissolved arsenic and mercury. Most samples were analyzed for major cations and anions, trace metals, redox species of arsenic, iron, nitrogen, and sulfur, and isotopes of hydrogen and oxygen. Radiogenic isotopes of strontium and tritium concentrations were also determined in selected samples. In addition, river and stream discharge data were obtained to determine the flux of chloride and other solutes from thermal areas in the southwest YNP.