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Wednesday, November 15, 2006

Adsorption of Linear Polyacrylamide to Fire-Affected (Hydrophobic) Soils.

Troy Bauder1, Jianhang Lu2, Todd Gaines1, and David Huber3. (1) Dept of Soil & Crop Sciences, Colorado State Univ, CD 1170, Fort Collins, CO 80523-1170, (2) Dept of Env Science, Univ of California, 900 University Ave, Riverside, CA 92521, (3) Arizona State Univ, 818 W 3rd St #136, Tempe, AZ 85281

Soil erosion and accompanying sedimentation to water bodies after forest fires can be severe due to loss of vegetative cover, litter, soil organic matter, and fired-induced soil hydrophobicity.  Linear, anionic polyacrylamide (PAM) significantly reduces erosion in furrow irrigation and construction sites, but little research has been conducted on its potential to control erosion or sedimentation after forest fires.  We investigated the interactions of PAM and burned soils to understand if PAM could be considered as a treatment following intense forest fires.  We collected soil samples from fire affected and nearby control sites.  Fire affected soils were identified as being strongly hydrophobic.  Flocculation, batch adsorption, and water-stable-aggregate distribution experiments were conducted on soil, ash, and depositional materials.  Flocculation was determined in soil/PAM solutions by measuring light transmittance.  PAM was measured during adsorption assays using size exclusion chromatography.  PAM increased flocculation as measured by increased transmittance in the both the control and burned soils using concentrations as low as 2.5 mg L-1.  Adsorption studies also showed that PAM had a similar affinity for burn and control soils, but less for the eroded depositional material, most likely due to the higher ash content.  Less PAM was adsorbed by the ash than the mineral portion of the intact samples confirming that the lower flocculation in the burn soils was likely due to ash content rather than mineral soil.  Adsorption of PAM tended to increase as surface tension increased suggesting hydrophobic soils have a slightly higher affinity for PAM. This study provided results that supported a potential role for PAM in reducing erosion and/or lowering sediment in waters from fire-affected landscapes.  Further field and laboratory research is needed on the best formulation, application timing, accompanying amendments, and environmental fate of PAM before sound recommendations can be made regarding use in these situations.