Nitrogen dynamics in the hyporheic zone of a forested stream during a small storm, Hokkaido, Japan

Hideaki Shibata, Osamu Sugawara, Hisano Toyoshima, Steven M. Wondzell, Futoshi Nakamura, Tamao Kasahara, Frederick J. Swanson, Kaichiro Sasa

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Abstract

Water and dissolved nitrogen flows through the hyporheic zone of a 3rd-order mountain stream in Hokkaido, northern Japan were measured during a small storm in August 1997. A network of wells was established to measure water table elevations and to collect water samples to analyze dissolved nitrogen concentrations. Hydraulic conductivity and the depth to bedrock were surveyed. We parameterized the groundwater flow model, MODFLOW, to quantify subsurface flows of both stream water and soil water through the hyporheic zone. MODFLOW simulations suggest that soil water inflow from the adjacent hill slope increased by 1.7-fold during a small storm. Dissolved organic nitrogen (DON) and ammonium (NH4+) in soil water from the hill slope were the dominant nitrogen inputs to the riparian zone. DON was consumed via mineralization to NH4+ in the hyporheic zone. NH 4+ was the dominant nitrogen species in the subsurface, and showed a net release during both base and storm flow. Nitrate appeared to be lost to denitrification or immobilized by microorganisms and/or vegetation in the riparian zone. Our results indicated that the riparian and hyporheic system was a net source of NH4+ to the stream.

Original languageEnglish
Pages (from-to)83-104
Number of pages22
JournalBiogeochemistry
Volume69
Issue number1
DOIs
Publication statusPublished - May 2004
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Environmental Chemistry
  • Water Science and Technology
  • Earth-Surface Processes

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