Iron is an important macronutrient for life an is also an essential electron donor and acceptor in microbial energy metabolism. Numerous, interdependent biological, chemical, and physical processes control the redox cycling of iron in sedimentary environments. In coastal sediments, ecosystem-engineering animals play a major top-down role controlling microbial populations and the biogeochemical transformations they catalyze. In this study, we analyzed the geochemical depth profiles of pore water and solid phase iron (Fe) in combination with the associated sedimentary microbial community in a bioturbated mudflat across on seasonal cycle.