The sensitivity of aquatic microbial communities to a complex agricultural contaminant depends on previous drought conditions

•Effects of river intermittency on phototrophic biofilm sensitivity to contamination.•Exposure to an agricultural run-off (ARO) after a dry period and/or warming.•Dry period duration and warming highly affected biofilms.•Biofilms were moderately impacted by contamination.•Biofilm sensitivity to ARO was lower after a short dry period.