These data were collected between February 2016 and August 2018 during the investigation of seasonal hydrologic connectivity between meteoric water and stream flow generation in Hyalite Canyon, MT (USA). We interpreted seasonal, longitudinal patterns of stable water isotope composition in stream flow as a method of determining stream flow generation mechanisms throughout the year. Longitudinal analysis allowed for the use of the isotopic lapse rate with elevation to assess when in the year meteoric water was reaching the stream, and when a more well-mixed source of water (i.e. ground waters) were the primary source of stream flow generation. This resource provides supplementary data and analysis code for seasonal stable water isotope and nitrate data for water samples collected in Hyalite Canyon, as well as stable water isotope data for precipitation (rain and snow) collected in Gallatin Valley and Hyalite Canyon throughout the study period. Computations for determining a prediction interval for the LMWL using a Monte Carlo resampling method are also included, as well as source code for figures included in the manuscript.

Sampling sites represent a longitudinal transect moving downstream through Hyalite Canyon along Hyalite Creek. Sampling sites included surface waters in Hyalite Creek and five tributaries, a spring and associated spring channel in the bank of Hyalite Creek, a well and associated cistern in neighboring Hodgman Canyon, and a well in the uppermost alluvial fan formed by Hyalite Creek at the mountain front. Surface waters were sampled in February, March, May, July, and August 2016-2018. Surface water samples were collected using a peristaltic pump (Geotech™ Denver, CO, United States) with platinum-cured Silicon tubing. Wells were sampled by purging three well volumes prior to water collection, employing the same filtration and field measures used at surface water sampling sites. Samples were filtered at the time of sampling using a 0.45 µm, mid-capacity capsule filter (Geotech™ Denver, CO, United States).

Chemical and isotopic analyses were conducted at the Montana State University (MSU) Environmental Analytical Lab (EAL) in Bozeman, MT. Nitrate concentrations were analyzed by Inductively Coupled Plasma - Optical Emission Spectroscopy (ICP-OES; Perkin Elmer™ Waltham, MA, United States). 18O and D isotopic analysis were conducted using using an off-axis integrated cavity output liquid water isotope analyzer (Los Gatos Research, San Jose, CA; Baer, Paul, Gupta, & O’Keefe, 2002) operated by the MSU EAL. Ten isotope analyses were performed per sample. The first two analyses were discarded during data processing to minimize potential for residual effects from previous samples. Reported data represent an average of the remaining eight analyses. Originally, four standards were used to bracket samples (Table S1): USGS 46 and USGS 48, as well as LGR #2C and LGR #3C. Sample runs included a set of all four standards inserted at the beginning and end of the run, as well as a standard inserted after every fourth sample.