|Blank, Robert - Bob|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/1/2009
Publication Date: 11/15/2009
Citation: Caldwell, T.G., Johnson, D.W., Miller, W.W., Qualls, R.G., Blank, R.R. 2009. Prescription Fire and Anion Retention in Tahoe Forest Soils. Soil Science. 174:594-600. Interpretive Summary: Prescribed burning is utilized to reduce fire potential in the Lake Tahoe Basin; however, subsequent nutrient loading to the lake is a major concern. We evaluated the effect of prescribed burning on leaching of ortho-phosphorus and sulfate on two common soil types in the Lake Tahoe Basin. In addition, laboratory studies were undertaken to evaluate how levels of post-fire ash affects mobility of phosphorous and sulfate. In both soil types, prescribed burning increased surface soil concentration of sulfate, but did not significantly affect concentration of ortho-phosphorus. Addition of ash to similar unburned soils greatly increased concentrations of sulfate, possibly due to decreased anion retention as higher pH’s, and decreased concentrations of ortho-phosphorus, possibly due to precipitation with calcium.
Technical Abstract: Prescribed burning is a possible option to reduce fire potential in the Lake Tahoe Basin (California and Nevada). However, subsequent nutrient loading to the lake is a major concern. The effect of residual ash on anion leaching, primarily O-PO4 and SO42-, was studied in both the field and laboratory following two understory prescription burns within the Tahoe National Forest. Sawtooth (SAW) and Marlene (MAR) field sites were chosen on the basis of the dominant parent materials found in the Tahoe Basin: andesite (AN) and decomposed granite (DG), respectively. Measured burn intensities varied greatly within and between sites with a mean soil temperature of 190 ± 168ºC at SAW and 402 ± 198ºC at MAR; and burn intensities were not correlated to any ion concentration. Soil samples collected immediately following prescribed fire and after snowmelt indicated that fire increased soil pH, Ca2+, and SO42- in both soils. No consistent trend was observed for O-PO4. Laboratory addition of ash to both SAW and MAR unburned soil also resulted in a substantial increase to both pH and SO42-. The increase in SO42- far exceeded amounts found on the ash and thus is hypothesized to be due to pH induced desorption from the unburned soil. Conversely, extractable O-PO4 decreased with increasing pH and SO42-. The reduction in O-PO4 with increasing pH is hypothesized to be due to increased precipitation with enriched post-burn Ca2+. Similar trends in both parent materials indicate that nutrient retention may be controlled by soil pH and ash. Concluding sentence, what are implication of research.