Using polyacrylamide to mitigate post-fire soil erosion

- Granular anionic polyacrylamide (PAM) was tested to reduce post-fire soil erosion.
- PAM increased runoff in the 1st storm due to changes in runoff and soil solution viscosities.
- This effect was reversed after one drying cycle.
- The application of PAM reduced soil loss in three consecutive storms.
- Field experiments in a burnt forest of Israel confirmed the laboratory results.

One of the consequences of wildfires is the modification of the hydrology of the affected area, usually resulting in increased overland flow and soil erosion. In this work, we tested granular anionic polyacrylamide (PAM) to reduce post-fire soil erosion, and the mechanisms by which this polymer modifies infiltration rate (IR), runoff and soil loss. Two contrasting soils affected by fire were exposed to three consecutive simulated rainstorms separated by drying periods. During the 1st rainstorm, PAM decreased IR and increased runoff in both soils while soil loss was reduced compared to the untreated controls. In the following storms, the reduction in soil loss persisted, but the effect of PAM on IR and runoff was reversed. The reduction of soil loss was attributed to two mechanisms: (i) an increase of the viscosities of runoff and soil solution as PAM dissolved during the 1st storm, which resulted in more runoff but with reduced erosivity; and (ii) the stabilization of soil aggregates throughout the 1st rainstorm and drying period, when PAM was irreversibly adsorbed to soil particles. Field erosion plots constructed on a burnt area in Birya forest, Israel, confirmed the laboratory results. The application of 25 and 50 kg ha− 1 of granular PAM reduced soil erosion by 23 and 57%, respectively, compared to the untreated control. We suggest that granular PAM could be an alternative to current post-fire erosion mitigation measures.