Wildfire and prescribed burning effects on nitrogen dynamics in central Idaho watershed ecosystems


Stephan, Kirsten.. (2007). Wildfire and prescribed burning effects on nitrogen dynamics in central Idaho watershed ecosystems. Theses and Dissertations Collection, University of Idaho Library Digital Collections.

Wildfire and prescribed burning effects on nitrogen dynamics in central Idaho watershed ecosystems
Stephan, Kirsten.
Watersheds--Nitrogen content--Effect of fires on--Idaho Nitrogen--Fixation--Idaho Wildfires--Idaho
Natural Resources
Wildfire, a common natural disturbance in many biomes, can have profound effects on nitrogen (N) dynamics in both terrestrial and aquatic ecosystems. Therefore, the objective of this study was to improve the understanding of post-fire N dynamics in small watersheds that experienced different fire severities. This was achieved by quantifying and interpreting the N concentrations and N isotopic signatures of soil, understory plants, streamwater and aquatic biota in paired watersheds (burned-unburned) for two to four years after wildfire and spring prescribed burns in a total of eight independent sites.;After wildfires, short-term increases in inorganic N concentrations in mineral soil and streamwater resulted in increased N concentration in terrestrial plants and in-stream moss, providing analogous and important N retention mechanisms in the terrestrial and aquatic ecosystem components. The temporal disconnect between major losses of available N from the soil during snowmelt and the onset of the growing season highlighted the importance of aquatic N retention.;After spring prescribed burns, increases in soil inorganic N concentrations and plant foliar N concentrations occurred as well, however the magnitude and/or duration of increase of available soil N was reduced relative to that after wildfires. In prescription-burned watersheds, there were no effects on the aquatic ecosystem component due to the complete retention of post-fire available N by plants and the soil microbial community within either the burned or downhill unburned areas.;The use of N stable isotopes at natural abundance confirmed the differences between effects of wildfire and spring prescribed burns. A directly fire-induced isotopic signal in soil, in combination with altered soil N transformation processes, resulted in the isotopic enrichment of linked N pools (plants, streamwater, in-stream moss) after wildfires. Only plant foliage was enriched after spring prescribed burns, although to a lesser degree than after wildfire. Thus, isotopic shifts in terrestrial plant foliage or aquatic biota after fire are a useful indicator of the spatial extent, magnitude, and duration of fire effects and the fate of post-fire available N.;The watershed-ecosystem approach applied to first-order coniferous watersheds furthered the understanding of complex interactions between the terrestrial and aquatic components with regard to post-fire N dynamics.
Thesis (Ph. D., Natural Resources)--University of Idaho, July 2007.
Major Professor:
Kathleen L. Kavanagh.
Defense Date:
July 2007.
Format Original:
x, 127 leaves :col. ill., map ;29 cm.

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