Incubation　experiments　were　adopted　to　characterize　the　rates　and　pathways　of　iron　reduction　and　the　contributions　to　anaerobic　organic　matter　mineralization　in　the　upper　0-5　cm　of　sediments　along　a　landscape-scale　inundation　gradient　in　tidal　marsh　sediments　in　the　Min　River　Estuary,　Southeast　China.　Similar　sediment　characteristics,　single-species　vegetation,　varied　biomass　and　bioturbation,　distinct　porewater　pH,　redox　potential,　and　electrical　conductivity　values　have　resulted　in　a　unique　ecogeochemical　zonation　along　the　inundation　gradient.　Decreases　in　solid-phase　Fe(III)　and　increases　in　nonsulfidic　Fe(II)　and　iron　sulfide　were　observed　in　a　seaward　direction.　Porewater　Fe2+　was　only　detected　in　the　upland　area.　High　rates　of　iron　reduction　were　observed　in　incubation　jars,　with　significant　accumulations　of　nonsulfidic　Fe(II),　moderate　accumulations　of　iron　sulfides,　and　negligible　accumulations　of　porewater　Fe2+.　Most　of　the　iron　reduction　was　microbially　mediated　rather　than　coupled　to　reduced　sulfides.　Microbial　iron　reduction　accounted　for　20-89　%　of　the　anaerobic　organic　matter　mineralization　along　the　inundation　gradient.　The　rate　and　dominance　of　microbial　iron　reduction　generally　decreased　in　a　seaward　direction.　The　contributions　of　microbial　iron　reduction　to　anaerobic　organic　matter　mineralization　depended　on　the　concentrations　of　bioavailable　Fe(III),　the　spatial　distribution　of　which　was　significantly　related　to　tidal　inundation.　Our　results　clearly　showed　that　microbial　iron　reduction　in　the　upper　sediments　along　the　gradient　is　highly　dependent　on　spatial　scales　controlled　primarily　by　tidal　inundation.