|Blank, Robert - Bob|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2006
Publication Date: 4/1/2006
Citation: Murphy, J.D., Johnson, D.W., Miller, W.W., Walker, R.F., Carrol, E.F., Blank, R.R. 2006. Wildfire effects on soil nutrients and leaching in a Tahoe Basin watershed. Journal of Environmental Quality. 35:479-489. Interpretive Summary: Excess nutrient transport to Lake Tahoe following prescribed forest burning is an environmental concern. We took advantage of a wildfire that consumed a previously established research area to document the effects of fire on soil nutrients. Long-term ecological effects of the wildfire were loss of forest floor and surface mineral soil nitrogen. Important short-term affects are increased levels of inorganic nitrogen and sulfate, which being mobile in the soil, can potentially move into Lake Tahoe.
Technical Abstract: A wildfire burned through 9 of 16 plots previously established for a prescribed fire/mechanical treatment study in a mixed conifer forest in the Lake Tahoe Basin, Nevada. As a result, we were able to accurately estimate the effects of the fire on forest floor carbon and nutrient contents, soil chemical changes, soil solution, and soil leaching fluxes using pre- and post-fire comparisons as well as controls. These analyses showed that the fire and post-fire erosion caused large and statistically significant losses of C, N, P, S, K, Ca, and Mg from the forest floor. The fire also caused significant losses of C and N in surface soil horizons, but increases in water-extractable SO42- in all horizons, and increases in pH in most horizons one year after the burn. The pH increases were accompanied by apparent increases in exchangeable Ca2+, but the latter were not statistically significant. The fire had no statistically significant effects on exchangeable Mg2+ or on Bray-, bicarbonate, or water-extractable-P concentrations in soils. Effects on exchangeable K+ were limited to an apparent increase in the C horizon, which we suspect was spurious. During the first winter after the fire, soil solution concentrations of NH4+, NO3- , ortho-P, and (especially) SO42- were elevated in the burned area compared to the control area, and resin lysimeters showed significant increases in the leaching of NH4+ and mineral N. Resin lysimeters showed no effect of the fire on ortho-P leaching. We conclude that the most ecologically significant long-term effect of the fire on the terrestrial ecosystem was the large losses of N from forest floor and soils, and the most ecologically significant short-term effect was the large increases in the leaching of mineral N and SO42-.