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Nitrate Pathways, Processes, and Timing in an Agricultural Karst System: Development and Application of a Numerical Model
Husic, A. Fox, J. Adams, E. Ford, W. Agouridis, C. Currens, J. Backus, J.
Husic, A.
Fox, J.
Adams, E.
Ford, W.
Agouridis, C.
Currens, J.
Backus, J.
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Abstract
Nitrogen (N) contamination within agriculturalākarst landscapes and aquifers is widely reported; however, the complex hydrological pathways of karst make N fate difficult to ascertain. We developed a hydrologic and N numerical model for agriculturalākarst, including simulation of soil, epikarst, phreatic, and quick flow pathways as well as biochemical processes such as nitrification, mineralization, and denitrification. We tested the model on four years of nitrate (NO3ā) data collected from a phreatic conduit and an overlying surface channel in the Cane Run watershed, Kentucky, USA. Model results indicate that slow to moderate flow pathways (phreatic and epikarst) dominate the N load and account for nearly 90% of downstream NO3ā delivery. Further, quick flow pathways dilute NO3ā concentrations relative to background aquifer levels. Net denitrification distributed across soil, epikarst, and phreatic water removes approximately 36% of the N inputs to the system at rates comparable to nonkarst systems. Evidence is provided by numerical modeling that NO3ā accumulation via evapotranspiration in the soil followed by leaching through the epikarst acts as a control on spring NO3ā concentration and loading. Compared to a fluvialādominated immature karst system, matureākarst systems behave as natural detention basins for NO3ā, temporarily delaying NO3ā delivery to downstream waters and maintaining elevated NO3ā concentrations for days to weeks after hydrologic activity ends. This study shows the efficacy of numerical modeling to elucidate complex pathways, processes, and timing of N in karst systems.
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An edited version of this paper was published by AGU. Copyright 2019 American Geophysical Union.
Date
2019-02-25
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Wiley
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Husic_2019.pdf
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Husic, A., Fox, J., Adams, E., Ford, W., Agouridis, C., Currens, J., & Backus, J. (2019). Nitrate pathways, processes, and timing in an agricultural karst system: Development and application of a numerical model. Water Resources Research, 55, 2079ā 2103. https://doi.org/10.1029/2018WR023703