Wednesday, November 15, 2006

Mechanical Harvest and Prescribed Fire Effects on Sierran Watershed Runoff Water Quality.

Watkins Miller1, T. M. Loupe2, D. W. Johnson1, E. M. Carroll1, J. D. Murphy1, C. Stein1, and R.F. Walker1. (1) Natural Resources & Env Science, 1000 Valley Rd, Reno, NV 89512-0013, (2) Univ of Nevada, 1000 Valley Rd, Reno, NV 89512

Fire suppression and the lack of mechanical harvest in many areas of the eastern Sierra Nevada has left forested areas with dense trees, high fuel loads, and a thick layer of organic litter. Furthermore, recent research has recorded extremely high concentrations of inorganic nitrogen (ammonium, nitrate), phosphorus (ortho-phosphate), and sulfur (sulfate) in surface runoff from these Sierran watersheds. The effects biomass reduction using controlled burning and cut-to-length mechanical harvest followed by chip mastication on surface runoff water quality (N, P, and S) were evaluated. In both unburned treatments (unburned/unharvested, unburned/harvested) there was a clear temporal effect between years 1 (pre-burn) and 2 (post-burn), with higher runoff nutrient loads measured during year 2 of the study. Only SO42--S loading was found to increase significantly following mechanical harvest alone. Total nutrient discharge loading of NH4+-N, NO3--N, PO43--P, and SO42--S was increased by burning, but more so for the burned unharvested than the burn harvested treatments. The combined effects of mechanical harvest and burning were less than burning alone. This suggests that in the absence of biomass reduction, wildfire has the potential to dramatically increase the nutrient content in surface runoff.