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.