loading page

Linking water age, nitrate export regime, and nitrate isotope biogeochemistry in a tile-drained agricultural field
  • +5
  • Zhongjie Yu,
  • Yinchao Hu,
  • Lowell E Gentry,
  • Wendy H Yang,
  • Andrew J Margenot,
  • Kaiyu Guan,
  • Corey A Mitchell,
  • Minpeng Hu
Zhongjie Yu
University of Illinois at Urbana Champaign

Corresponding Author:[email protected]

Author Profile
Yinchao Hu
Unknown
Author Profile
Lowell E Gentry
University of Illinois at Urbana-Champaign
Author Profile
Wendy H Yang
University of Illinois at Urbana Champaign
Author Profile
Andrew J Margenot
University of Illinois at Urbana-Champaign
Author Profile
Kaiyu Guan
University of Illinois at Urbana Champaign
Author Profile
Corey A Mitchell
University of Illinois at Urbana-Champaign
Author Profile
Minpeng Hu
University of Illinois at Urbana-Champaign
Author Profile

Abstract

Recent theoretical advances related to time-variant water age in hydrologic systems have opened the door to a new method that probes water mixing and selection behaviors using StorAge Selection (SAS) functions. In this study, SAS functions were applied to investigate storage, water mixing behaviors, and nitrate (NO3-) export regimes in a tile-drained corn-soybean rotation field in the Midwestern United States. The natural abundance stable nitrogen and oxygen isotopes of tile drainage NO3- were also measured to provide constraints on biogeochemical NO3- transformations. The SAS functions calibrated using chloride measurements at tile drain outlets revealed a strong young water preference during tile discharge generation. The use of a time-variant SAS function for tile discharge generated unique water age dynamics that reveals an inverse storage effect driven by activation of preferential flow paths and mechanically explains the observed variations in NO3- isotopes. Combining the water age estimates with NO3- isotope fingerprinting delineated NO3- export dynamics at the tile-drain scale, where a lack of strong contrast in NO3- concentration across the soil profile results in chemostatic NO3- export regimes. For the first time, NO3- isotopes were embedded into a water age-based transport model to model reactive NO3- transport under transient conditions. Results from this modeling study provided a proof-of-concept for the potential of coupled water age modeling and NO3- isotope analysis in elucidating complex mechanisms that control the coupled water and NO3- transport. Further integration of water age theory and NO3- isotope biogeochemistry is expected to significantly improve reactive NO3- transport modeling.
30 Mar 2023Submitted to ESS Open Archive
03 Apr 2023Published in ESS Open Archive