Yellowstone National Park (YNP; Wyoming, Montana, and Idaho, USA) contains more than 10,000 hydrothermal features, several lakes, and four major watersheds. For more than 140 years, researchers at the U.S. Geological Survey and other scientific institutions have investigated the chemical compositions of hot springs, geysers, fumaroles, mud pots, streams, rivers, and lakes in YNP and surrounding areas. Water chemistry studies have revealed a range of compositions including waters with pH values ranging from about 1 to 10, surface temperatures from ambient to superheated values of 95°C, and elevated concentrations of silica, lithium, boron, fluoride, mercury, and arsenic. Hydrogeochemical data from YNP research have led to insights on subsurface conditions of temperature and chemistry, water-rock-gas interactions and processes of high-temperature mineral alteration with dissolution and precipitation, redox processes, thermophilic microbial metabolism under extreme conditions and effects of thermal water chemistry on river systems. In this Data Release, water chemistry data for 4,918 water samples are reported for numerous thermal features, rivers, streams, lakes, drillholes, and precipitation in and around YNP. The data for these samples were originally located in 38 reports published between 1888 and 2022 and in multiple unpublished documents. Spanning more than 600 unique sampling sites throughout the YNP region, this dataset includes samples collected as early as 1883 (Gooch & Whitfield, 1888) and as recently as 2021 (McCleskey, et al, 2022). The thermal features sampled most frequently include Cistern Spring (180 samples) and Echinus Geyser (73 samples) in Norris Geyser Basin and Ojo Caliente Spring (143 samples) in the Lower Geyser Basin, while more than 500 sites have 5 samples or fewer. Water chemistry data from thermal features, rivers, and streams are most represented, comprising 75% (thermal) and 17% (rivers/streams) of the dataset. Across all major areas of the park, Norris Geyser Basin has been sampled more than any other basin, with more than 1,100 samples reported in this dataset.

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.

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.

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.

Yellowstone River at Yellowstone Lake Outlet (YYFB), Yellowstone National Park Sample Collection: Samples were collected near the USGS stream gage 06186500 (Latitude 44°34'01.53", Longitude 110°22'49.46" NAD83). At the time of collection, all waters samples were filtered through a syringe filter (0.45-micrometer). Two splits of the filtered water were retained for chemical analyses, including an unacidified (FU) sample for determination of anion concentrations and a nitric acid preserved (FA; 1% volume-to-volume concentrated trace-metal grade nitric acid) sample for cation and trace metal analyses. During sample collection, the water temperature, specific conductance, and pH were often measured. Sample Analyses: Concentrations of chloride, fluoride, bromide, and sulfate were determined with an ion chromatograph (Dionex ICS-2000). Analytical errors for these constituents were typically less than 2%. Total alkalinity as bicarbonate was determined on stored samples, usually within several months after collection. Ten milliliters of sample were titrated with 0.05 Normal sulfuric acid to the bicarbonate end-point. The analytical error in alkalinity concentrations was roughly ± 5%. Concentrations of cations and trace metals were determined with an inductively coupled plasma-optical emission spectroscopy (Perkin Elmer Optima 7300 DV) following the methods described in Ball and others (2010). Database Contents The data file (YYFB.csv) contains the solute concentrations and the water discharge at the time of sampling for each of the rivers studied. The entries in the data file appear in the following columns: A. Date sample collected B. Time sample collected C. Water discharge (cubic feet per second) obtained from the U.S. Geological Survey's National Water Information System (NWIS) D. Water discharge (cubic meter per second) - obtained by multiplying column C by 0.02832 E. Chloride concentration (milligrams per liter) F. Fluoride concentration (milligrams per liter) G. Bromide concentration (milligrams per liter) H. Sulfate concentration (milligrams per liter) I. Alkalinity (milligrams per liter as bicarbonate) J. Chloride flux (grams/second) K. pH (standard units) L. Specific conductance (microSiemens per centimeter) M. Temperature (degrees Celsius) N. Calcium concentration (milligrams per liter) O. Magnesium concentration (milligrams per liter) P. Sodium concentration (milligrams per liter) Q. Potassium concentration (milligrams per liter) R. Iron concentration (milligrams per liter) S. Silica concentration (milligrams per liter) T. Boron concentration (milligrams per liter) U. Aluminum concentration (milligrams per liter) V. Lithium concentration (milligrams per liter) W. Strontium concentration (milligrams per liter) X. Barium concentration (milligrams per liter) Y. Rubidium concentration (milligrams per liter) Z. Manganese concentration (milligrams per liter) AA. Molybdenum concentration (milligrams per liter) AB. Copper concentration (milligrams per liter) AC. Zinc concentration (milligrams per liter) AD. Cadmium concentration (milligrams per liter) AE. Chromium concentration (milligrams per liter) AF. Cobalt concentration (milligrams per liter) AG. Lead concentration (milligrams per liter) AH. Nickel concentration (milligrams per liter) AI. Vanadium concentration (milligrams per liter) AJ. Arsenic concentration (milligrams per liter) AK. Antimony concentration (milligrams per liter) References Ball, J.W., McCleskey, R.B., and Nordstrom, D.K., 2010, Water-chemistry data for selected springs, geysers, and streams in Yellowstone National Park, Wyoming, 2006-2008: U.S. Geological Survey Open-File Report 2010-1192, 109 p.

Monitoring the chloride (Cl) flux in the major rivers draining Yellowstone National Park (YNP) provides a holistic view of the thermal output from the underlying magma reservoir, and abrupt fluctuations in the Cl flux may signify changes in hydrothermal activity. The U.S. Geological Survey (USGS) and the National Park Service (NPS) have collaborated on Cl flux monitoring of the major rivers since the 1970s. In the past, researchers collected water samples from the major rivers in YNP, but funding restrictions, winter conditions, and the great distances between sites limited the number of samples collected annually. Beginning in 2010, specific conductance, which is relatively easy to measure and can be automated, has been used as a proxy for Cl. The use of specific conductance probes at the various monitoring sites enables a more consistent estimation of Cl flux. Consistent monitoring is useful to identify changes in river chemistry due to geyser eruptions, rain events, or changes in thermal inputs caused by earthquakes or other natural events. The use of specific conductance as a proxy for Cl requires quantification of the relationship between specific conductance, Cl, and other geothermal solutes and the relationship needs to be periodically verified. This data release contains specific conductance measurements (every 15 minutes) and water chemistry data from monitoring sites along the Madison River, Firehole River, Gibbon River, Snake River, Gardner River, Fall River, Yellowstone River, and Tantalus Creek. For several sites, there are periods of time when specific conductance is not reported because the data was likely unreliable due to failure or fouling of the specific conductance probe. There are also specific conductance and discharge data available from the USGS National Water Information System (USGS NWIS, https://waterdata.usgs.gov/nwis/rt). The following list details the sites included in this data release and the National Water Information System site identification numbers. Yellowstone River near Corwin Springs, 06191500; Gardner River near Mammoth, 06191000; Firehole River near West Yellowstone, 06036905; Firehole River at Old Faithful, 06036805; Fall River near Squirrel, Idaho, 13046995; Gibbon River at Madison Junction, 06037100; Madison River near West Yellowstone, 06040000; Snake River near Flagg Ranch WY, 13010065; and Tantalus Creek at Norris Junction, 06036940. First posted - January 28, 2019 (available from author) Revised - May 6, 2020 (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.

Monitoring the chloride (Cl) flux in the major rivers draining Yellowstone National Park (YNP) provides a holistic view of the thermal output from the underlying magma reservoir, and abrupt fluctuations in the Cl flux may signify changes in hydrothermal activity. The U.S. Geological Survey (USGS) and the National Park Service (NPS) have collaborated on Cl flux monitoring of the major rivers since the 1970s. In the past, researchers collected water samples from the major rivers in YNP, but funding restrictions, winter conditions, and the great distances between sites limited the number of samples collected annually. Beginning in 2010, specific conductance, which is relatively easy to measure and can be automated, has been used as a proxy for Cl. The use of specific conductance probes at the various monitoring sites enables a more consistent estimation of Cl flux. Consistent monitoring is useful to identify changes in river chemistry due to geyser eruptions, rain events, or changes in thermal inputs caused by earthquakes or other natural events. The use of specific conductance as a proxy for Cl requires quantification of the relationship between specific conductance, Cl, and other geothermal solutes and the relationship needs to be periodically verified. This data release contains specific conductance measurements (every 15 minutes) and water chemistry data from monitoring sites along the Madison River, Firehole River, Gibbon River, Snake River, Gardner River, Fall River, Yellowstone River, and Tantalus Creek. For several sites, there are periods of time when specific conductance is not reported because the data was likely unreliable due to failure or fouling of the specific conductance probe. There are also specific conductance and discharge data available from the USGS National Water Information System (USGS NWIS, https://waterdata.usgs.gov/nwis/rt). The following list details the sites included in this data release and the National Water Information System site identification numbers. Yellowstone River near Corwin Springs, 06191500; Gardner River near Mammoth, 06191000; Firehole River near West Yellowstone, 06036905; Firehole River at Old Faithful, 06036805; Fall River near Squirrel, Idaho, 13046995; Gibbon River at Madison Junction, 06037100; Madison River near West Yellowstone, 06040000; Snake River near Flagg Ranch WY, 13010065; and Tantalus Creek at Norris Junction, 06036940. First posted - January 28, 2019 (available from author) Revised - May 6, 2020 (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.

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.

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.