Isotopic signals in an agricultural watershed suggest denitrification is locally intensive in riparian areas but extensive in upland soils  data and code

Citation
Sigler, W. A., S. A. Ewing, S. D. Wankel, S. Leuthold, R. Payn, C. A. Jones (2022). Isotopic signals in an agricultural watershed suggest denitrification is locally intensive in riparian areas but extensive in upland soils  data and code, HydroShare.  https://doi.org/10.4211/hs.f9f36a39190e4cc6a7cdc0cd0cc9bdd6

Summary
The data and R code provided here are the underpinnings of a manuscript in the journal, Biogeochemistry (the manuscript title is parallel to resource title). Nitrogen use efficiency in cultivated agriculture is reduced by denitrification and by leaching of nitrate, which reduces water quality and is subject to denitrification downstream. Denitrification and leaching losses from dryland farming during fallow periods (no crop growing) can play a disproportionately large role in cropping system nitrogen losses. This work combines nitrogen mass balance with ?15N mass balance to estimate denitrification rates in soil relative to groundwater and streams.

Data includes solute concentrations and isotopic composition of nitrate and water in water samples collected from soil, groundwater and surface water.  Soil solution chemistry was characterized in samples from tension lysimeters installed in two non-irrigated fields operated by cooperating farmers. Groundwater and surface water sampling between 2012 and 2017 included two wells, five springs, and three stream sites. Solute concentration and water isotope analysis was conducted in the Montana State University Environmental Analytical Laboratory. Nitrate isotope analyses were conducted at Woods Hole Oceanographic Institution. For detailed analytical methods, see the main manuscript.

Software/Hardware
This code was successfully run in December 2021 using R version 4.1.2, with a PC running Windows 10, 64-bit operating system. R packages used in the analysis include: lubridate, reshape2, modeest, plotrix.

Contact
W. Adam Sigler
Check my ORCiD for my current email address
https://orcid.org/0000-0002-4815-0580

Rights
The original data presented here are available under CC-BY 4.0 https://creativecommons.org/licenses/by/4.0/legalcode

The code presented here is available under the MIT license. 
https://opensource.org/licenses/MIT

R packages used within the code (lubridate; reshape2; modeest, plotrix) all carry GPL-2, GPL-3, or MIT licenses. 

Purpose
The objective of this work is to understand the role of denitrification as a pathway of nitrogen loss across hydrologically connected soils, groundwater, and stream corridors in non-irrigated agricultural systems. The study area in the Judith River Watershed is in the headwaters of the Missouri River with a semi-arid climate (mean annual precipitation = 389 mm). The shallow aquifers and streams in the study area are well-suited to research on variation in the controls on denitrification due to well-defined hydrologic boundaries, and soils of varying thicknesses and textures that dictate a range of water storage and biogeochemical conditions. This resource provides the chemical and isotopic data as well as the code for conducting the Monte Carlo analysis for estimating soil denitrification rates and data visualization.

Related Resources
Sigler, W. Adam, Stephanie A. Ewing, Scott D. Wankel, Clain A Jones, Sam Leuthold, E. N. Jack Brookshire, Robert A. Payn. In press. Isotopic signals in an agricultural watershed suggest denitrification is locally intensive in riparian areas but extensive in upland soils. Biogeochemistry. https://doi.org/10.1007/s10533-022-00898-9

Funding Agencies
This work was funded by the United States Department of Agriculture, National Institute of Food and Agriculture [grant number 2011-51130-31121, 2011] and USDA NIFA grant number 2016-67026-25067. Additional funding was provided by MSU Extension, Montana Fertilizer Advisory Committee, the Montana Agricultural Experiment Station, MSU Vice President of Research, MSU College of Agriculture, and the Montana Institute on Ecosystems. This work was supported in part by the National Science Foundation EPSCoR Track 1 award to the Consortium for Research on Environmental Water Systems, Cooperative Agreement OIA-1757351, as well as NSF EPSCoR Track 1 award numbers OIA-1443108 and EPS-1101342.

Contributors
Fordyce, Simon. Montana State University Central Agricultural Research Center 
Bayrd, Venice. Montana State University; Montana EPSCoR