R. Blaine McCleskey David A. Roth Jefferson D. Hungerford Shaul Hurwitz Paul A. Bliznik 20190128 spreadsheet https://doi.org/10.5066/F7BP011G Measuring the thermal output of Yellowstone’s large magmatic system is not straightforward, as there are thousands of thermal features spread across 3470 square miles. One way to capture and integrate the contributions from this broad area is to monitor river chemistry, because thermal water discharge eventually enters a nearby river, which acts as a collection and delivery system. Nearly all the chloride in rivers that drain Yellowstone comes from emerging hot spring water heated underground by underlying magma. Monitoring river chemistry is therefore an important way to track the behavior and overall changes in Yellowstone’s hydrothermal system. By monitoring the chloride flux, the hydrothermal discharge and heat flux from Yellowstone can be estimated and variations (both short- and long-term) can be used to identify changes in the deep hydrothermal system, earthquake activity, geyser eruptions, and other natural events (like floods and the impacts of wildfire). 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. First posted - January 28, 2019 (available from author) Revised - May 6, 2020 (version 2.0; available from author) Revised - May 1, 2025 (version 3.0) NOTE: While previous versions are available from the author, all the records in previous versions can be found in version 3.0. This data release contains specific conductance and temperature measurements (every 15 minutes) from the following river monitoring site: Gardner River near Mammoth, 5 km downstream from USGS Gage 06191000 (Latitude: 44.99234, Longitude: -110.69098, NAD83). 2010 2024 ground condition Complete As needed -110.72948 -110.66872 45.03738 44.97233 ISO 19115 Topic Category geoscientificInformation inlandWaters None Yellowstone, Specific Conductance USGS Metadata Identifier USGS:5e8be5dc82cee42d1344434e None Yellowstone National Park Public Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also contains copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner whenever applicable. The data have been approved for release and publication by the U.S. Geological Survey (USGS). Although the data have been subjected to rigorous review and are substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, the data are released on the condition that neither the USGS nor the U.S. Government may be held liable for any damages resulting from authorized or unauthorized use. Although the data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein. Users of the data are advised to read all metadata and associated documentation thoroughly to understand appropriate use and data limitations. R. Blaine McCleskey USGS Water Mission Area Research Chemist mailing and physical

3215 Marine Street, Suite E. 127

Boulder Colorado 80303 USA 303-541-3071 303-541-3084 rbmccles@usgs.gov A field project located in Yellowstone could not have succeeded without the support of the National Park Service scientists including Dan Mahony, Erin White, and Henry Heasler. We are also grateful to Kirk Nordstrom, James Ball, Margery Price, and Ethan Stevens who provided lab analyses, field assistance, or review. This study was conducted under research permit YELL‐SCI‐5194. Specific Conductance Data An In-Situ Aqua Troll 100 Data Logger was used to measure and store specific conductance and water temperature measurements. Specific conductance measurements were made every 15 minutes. The specific conductance and water temperature monitoring data were periodically checked against discrete measurements. The hand-held field meter used for discrete measurements and the continuous specific conductance probe were calibrated using NIST traceable standards and measurements were made following the procedure described in the USGS National Field Manual (USGS, 2019). Continuous specific conductance and temperature measurements that were known or thought to be in error are not reported. References U.S. Geological Survey National Field Manual, 2019, Specific conductance: U.S. Geological Survey Techniques and Methods, Book 9, Chapter A6.3, 15 p., https://doi.org/10.3133/tm9A6.3. Continuous specific conductance data was periodically checked against discrete hand-held measurements. There were periodic data gaps caused by fouling of the probe due to high sediment flows or ice formation. The specific conductance data reported here are final. There were periodic data gaps caused by fouling of the probe due to high sediment flows or ice formation. The discharge data (shown in figures) is subject to change at the discretion of National Water Information System (NWIS). The data release will be updated as new data become available. No formal positional accuracy tests were conducted No formal positional accuracy tests were conducted Specific Conductance Specific conductance and water temperature measurements were made every 15 minutes. An In-Situ Aqua Troll 100 Data Logger was used to measure and store specific conductance measurements. The specific conductance monitoring data were periodically checked against discrete measurements. The hand-held field meter used for discrete measurements and the continuous specific conductance probe were calibrated using NIST traceable standards and measurements were made following the procedure described in the USGS National Field Manual (USGS, 2019). All specific conductance measurements are reported at 25 degrees Celsius (°C) using ISO-7888 temperature compensation. The data were downloaded from the Aqua Troll 100 using compatible software from the manufacturer. References Cited ISO, 1985, Water Quality - Determination of Electrical Conductivity; ISO-7888; International Organization for Standardization: Geneva. U.S. Geological Survey National Field Manual, 2019, Specific conductance: U.S. Geological Survey Techniques and Methods, Book 9, Chapter A6.3, 15 p., https://doi.org/10.3133/tm9A6.3. 20250125 GardnerSCv3.csv Comma Separated Value (CSV) file containing data. Producer Defined Date_Time Date and time (Mountain Daylight Time) Producer Defined Date and time (Mountain Daylight Time) Specific_Conductance Specific conductance of water Producer Defined 111 1495 microSiemens per centimeter at 25 degrees Celsius 1 Water_Temperature Water temperature Producer Defined NA No Data Producer defined 2.4 37.6 degrees Celsius 0.1 GS ScienceBase U.S. Geological Survey mailing address

Denver Federal Center, Building 810, Mail Stop 302

Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. Digital Data https://doi.org/10.5066/F7BP011G None 20251125 R. Blaine McCleskey USGS Research Chemist mailing and physical

3215 Marine Street, Suite E. 127

Boulder Colorado 80303 USA (303) 541-3015 rbmccles@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998