Title:
Data supporting the manuscript 'Using Geophysical Observations of a Tracer Injection in a Riparian Aquifer to Explore How Bimodal Transport and Mixing Influences Nitrate Processing'

Citation:
Poole, J. W., Ewing, S. A., Payn, R. A., Mayernik, C. M., Irons, T. P. (2026). Data supporting the manuscript - Using Geophysical Observations of a Tracer Injection in a Riparian Aquifer to Explore How Bimodal Transport and Mixing Influences Nitrate Processing, HydroShare, http://www.hydroshare.org/resource/543c4c6793c5419fb472810e4a557558

The content of this resource includes data referenced in:
Mayernik, C. M., S. A. Ewing, M. D. Degrandpre, et al. 2025. “Riparian Processes in Semi-Arid Landscapes: Understanding Controls on Nitrate Loss and Sulfate Production in Agricultural Stream Corridors.” Journal of Geophysical Research: Biogeosciences 130: e2024JG008559.

Abstract:
Extensive application of nitrogen (N) fertilizer to increase crop yields can contribute excess nitrate to groundwater and surface water, raising health concerns for humans and ecosystems that depend on these water resources. In the Judith River Watershed (JRW) of central Montana, chronically high and increasing upland groundwater nitrate concentrations reflect leaching from non-irrigated, dryland, cultivated soils with limited water holding capacity. These shallow upland aquifers contribute high-nitrate groundwater to adjacent riparian corridors managed as cattle pastures. In these riparian corridors, nitrate concentrations are a function of hydrologic connections between streams and upland or riparian groundwater, mediated by the predominantly anaerobic biogeochemical activity associated with abundant organic matter and wetter soils, and depending on variation of the riparian soil and sediment composition. Here we assess the riparian substrate thought to control these hydrologic connections and biogeochemical conditions across two contrasting 700-m reaches of stream corridors draining the Moccasin Terrace (near Moccasin, Montana USA). We hypothesize that nitrate and other solute concentrations in individual riparian wells are controlled both by the texture of riparian substrate in contact with the well screening as well as relative hydrologic connections to the well location from the terrace groundwater, the stream channel, and the riparian groundwater. We test these hypotheses using shallow, near surface, electrical resistivity tomography (ERT) surveys, a salt tracer electrical conductivity manipulation experiment paired with timelapse ERT imaging, riparian groundwater sampling, and surveys of groundwater levels and hydraulic conductivity values at 15 shallow (< 1.5 m) wells. Our results reveal the size, character, and connectivity of the riparian aquifer, quantifying transport rates and interactions among riparian soils, sediments, and groundwater that attenuate nitrate loading from agricultural management practices to improve water quality.

Spatial coverage:
The general area sampled is represented by the bounding box, and the specific watershed within which we worked was the Judith River Basin (HUC-8: 10040103).

Description of Contents:
The folder “Riparian_Wells_ERT” contains the raw ERT data associated with riparian well imaging and the Means analysis results presented in 3.2.
The folder “Substrate_Model” includes all inputs and raw code associated with the modeling process associated in this paper, presented in section 3.5. 
The folder “Tracer_Test” includes raw ERT data associated with visualizing the NaCl salt plume and the raw conductivity responses at the control well RW02, injection well RW11, and observational wells RW13 and RW14.
The folder “Well_Information_and_Water_Quality” includes basic physical well parameters associated with each riparian well and the nitrate (mg/L) and hydraulic conductivity values for each well (m/day). The nitrate is presented as a summary for each well in the file “Louse_Creek_Nitrate_Ksat_stats” but the full data is contained in the file “Louse_Creek_Riparian_Wells_Nitrate”.


Licenses:
The data in this resource are licensed under the Creative Commons CC-0 1.0 Universal.
This work has been marked as dedicated to the public domain. See here for the full legal text: 
https://creativecommons.org/publicdomain/zero/1.0/

Contact:
Jack Poole, jack7poole@gmail.com