Bacterial community shifts in decomposing cowpats and the subsequent impacts on fecal source indicators for water quality monitoring

•Major bacterial community shifts were observed in decomposing cowpats.•Potential bacterial targets of fresh and aged bovine runoff were identified.•104 E. coli/100 mL were available for mobilization from decomposing cowpats (160 days)•Steroid ratios used as indicators of bovine fecal pollution were stable in cowpats.•CowM2 qPCR marker was a useful signal of fresh bovine pollution in waterways.