Crab bioturbation drives coupled iron-phosphate-sulfide cycling in mangrove and salt marsh soils

•DGT revealed highly heterogeneous labile S(-II) distribution and widespread hotspots.•Bioturbation and roots enhanced oxygen penetration and sulfur oxidation.•Bioturbation promoted pyrite formation accompanying alkalinity generation.•The Fe-S redox in crab burrow was insensitive to the surrounding convection flow.