Water repellency by volcanic ash interacting with organic matter: Incubation response and effect on infiltration

•WR by volcanic ash increases when incubated with various organic matter sources.•Commonly used WR indicators CA and WDPT were only partially related.•Lipids and pH of mixed litter and ash changed during incubations, parallel with WR.•Higher CA lowered the critical slope at which a water drops runs off the surface.•WR surface layer reduced infiltration, with indications of air entrapment.