Riparian zones attenuate nitrogen loss following bark beetle-induced lodgepole pine mortality

Joel A. Biederman, Thomas Meixner, Adrian A. Harpold, David E. Reed, Ethan D. Gutmann, Janelle A. Gaun, Paul Brooks

Research output: Contribution to journalArticle

6 Scopus citations

Abstract

A North American bark beetle infestation has killed billions of trees, increasing soil nitrogen and raising concern for N loss impacts on downstream ecosystems and water resources. There is surprisingly little evidence of stream N response in large basins, which may result from surviving vegetation uptake, gaseous loss, or dilution by streamflow from unimpacted stands. Observations are lacking along hydrologic flow paths connecting soils with streams, challenging our ability to determine where and how attenuation occurs. Here we quantified biogeochemical concentrations and fluxes at a lodgepole pine-dominated site where bark beetle infestation killed 50-60% of trees. We used nested observations along hydrologic flow paths connecting hillslope soils to streams of up to third order. We found soil water NO3 concentrations increased 100-fold compared to prior research at this and nearby southeast Wyoming sites. Nitrogen was lost below the major rooting zone to hillslope groundwater, where dissolved organic nitrogen (DON) increased by 3-10 times (mean 1.65 mg L-1) and NO3-N increased more than 100-fold (3.68 mg L-1) compared to preinfestation concentrations. Most of this N was removed as hillslope groundwater drained through riparian soils, and NO3 remained low in streams. DON entering the stream decreased 50% within 5 km downstream, to concentrations typical of unimpacted subalpine streams (~0.3 mg L-1). Although beetle outbreak caused hillslope N losses similar to other disturbances, up to 5.5 kg ha-1y-1 , riparian and in-stream removal limited headwater catchment export to -1y-1. These observations suggest riparian removal was the dominant mechanism preventing hillslope N loss from impacting streams.

Original languageEnglish (US)
Pages (from-to)933-948
Number of pages16
JournalJournal of Geophysical Research: Space Physics
Volume121
Issue number3
DOIs
StatePublished - Mar 1 2016

Keywords

  • bark beetle
  • biogeochemistry
  • forest disturbance
  • hydrology
  • land cover change
  • nitrogen

ASJC Scopus subject areas

  • Soil Science
  • Forestry
  • Water Science and Technology
  • Palaeontology
  • Atmospheric Science
  • Aquatic Science
  • Ecology

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