Wildfire Effects on Soil Nutrients and Leaching in a Tahoe Basin Watershed

Abstract

A wildfire burned through a previously sampled research site, allowing pre- and post-burn measurements of the forest floor, soils, and soil leaching near Lake Tahoe, Nevada. Fire and post-fire erosion caused large and statistically significant (P < or = 0.05) losses of C, N, P, S, Ca, and Mg from the forest floor. There were no statistically significant effects on mineral soils aside from a decrease in total N in the surface (A11) horizon, an increase in pH in the A11 horizon, and increases in water-extractable SO4(2-) in the A11 and A12 horizons. Burning caused consistent but nonsignificant increases in exchangeable Ca2+ in most horizons, but no consistent or statistically significant effects on exchangeable K+ or Mg2+, or on Bray-, bicarbonate-, or water-extractable P concentrations. Before the burn, there were no significant differences in leaching, but during the first winter after the fire, soil solution concentrations of NH4+, NO3-, ortho-P, and (especially) SO4(2-) were elevated in the burned area, and resin lysimeters showed significant increases in the leaching of NH4+ and mineral N. The leaching losses of mineral N were much smaller than the losses from the forest floor and A11 horizons, however. We conclude that the major short-term effects of wildfire were on leaching whereas the major long-term effect was the loss of N from the forest floor and soil during the fire.

Moisture effects on carbon and nitrogen emission from burning of wildland biomass

“…These materials were then segregated into: 1) litter (the surface layer which is not in an advanced stage of decomposition, typically consisting of freshly fallen and dried leaves, needles, twigs, stems, bark, and fruits; 2) duff (the layer dominated by partially to fully decaying leaves and branches); and 3) topsoil (mixture of mineral soil, humus, and/or degraded organic material). Topsoil was examined because Murphy et al (2006) found that wild fires nearly deplete C and N in soils. Common aboveground shrubs were also collected and separated in the laboratory into leaves and stems of different diameters.…”

A Synthesis of Sierran Forest Biomass Management Studies and Potential Effects on Water Quality

“…Wildfire was found to induce an immediate mobilization of inorganic N and P [53]. Although small compared to volatilization losses, N leaching fluxes ( Figure 5A) from resin lysimeter measurements demonstrated significant (p < 0.05) increases 2 years post fire, with a shift from NH 4 + to NO 3 − (nitrite + nitrate) N between post burn years 1 and 2 [53][54] and a sharp decline in year 3.…”

“…Although small compared to volatilization losses, N leaching fluxes ( Figure 5A) from resin lysimeter measurements demonstrated significant (p < 0.05) increases 2 years post fire, with a shift from NH 4 + to NO 3 − (nitrite + nitrate) N between post burn years 1 and 2 [53][54] and a sharp decline in year 3. On the other hand, P leaching fluxes ( Figure 5B) showed no immediate change post burn, but a significant (p < 0.10) increase in post burn year 2.…”

“…This latter effect appeared to continue during post burn year 3, but due to the high variability among data, significance was lost. Soil solution chemistry was also obtained from suction lysimeter samples [53,54]. There was a significant (p < 0.05) increase in soil solution Figure 5A.…”

Long and Short-Term Effects of Fire on Soil Charcoal of a Conifer Forest in Southwest Oregon

“…Direct measurements of pre-and post-wildfire samples render assumptions concerning pre-fire conditions unnecessary. Studies in which soil C measurements are available before and after wildfires are rare and lack mention of the presence or absence of charcoal [21][22][23][24].…”