Regional variability of nitrate fluxes in the unsaturated zone and groundwater, Wisconsin, USA

Christopher T. Green; Lixia Liao; Bernard T. Nolan; Paul F. Juckem; Christopher L. Shope; Anthony J. Tesoriero; Bryant C. Jurgens

doi:10.1002/2017wr022012

USGS · 70195031

Regional variability of nitrate fluxes in the unsaturated zone and groundwater, Wisconsin, USA

Christopher T. Green·Lixia Liao·Bernard T. Nolan·Paul F. Juckem·Christopher L. Shope·Anthony J. Tesoriero·Bryant C. Jurgens

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Abstract

Process-based modeling of regional NO3− fluxes to groundwater is critical for understanding and managing water quality, but the complexity of NO3− reactive transport processes make implementation a challenge. This study introduces a regional vertical flux method (VFM) for efficient estimation of reactive transport of NO3− in the vadose zone and groundwater. The regional VFM was applied to 443 well samples in central-eastern Wisconsin. Chemical measurements included O2, NO3−, N2 from denitrification, and atmospheric tracers of groundwater age including carbon-14, chlorofluorocarbons, tritium, and tritiogenic helium. VFM results were consistent with observed chemistry, and calibrated parameters were in-line with estimates from previous studies. Results indicated that (1) unsaturated zone travel times were a substantial portion of the transit time to wells and streams (2) since 1945 fractions of applied N leached to groundwater have increased for manure-N, possibly due to increased injection of liquid manure, and decreased for fertilizer-N, and (3) under current practices and conditions, approximately 60% of the shallow aquifer will eventually be affected by downward migration of NO3−, with denitrification protecting the remaining 40%. Recharge variability strongly affected the unsaturated zone lag times and the eventual depth of the NO3− front. Principal components regression demonstrated that VFM parameters and predictions were significantly correlated with hydrogeochemical landscape features. The diverse and sometimes conflicting aspects of N management (e.g. limiting N volatilization versus limiting N losses to groundwater) warrant continued development of large-scale holistic strategies to manage water quality and quantity.

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Source-reported bounding extent: 42.48830197960227° to 47.279229002570794° latitude; -92.85644531250001° to -86.7041015625° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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BibTeX RIS

Christopher T. Green, Lixia Liao, Bernard T. Nolan, Paul F. Juckem, Christopher L. Shope, Anthony J. Tesoriero, Bryant C. Jurgens. 2018-01-23. Regional variability of nitrate fluxes in the unsaturated zone and groundwater, Wisconsin, USA. https://doi.org/10.1002/2017wr022012

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