Chemical　(via　buffered　ascorbate-citrate)　and　microbial　(via　Shewanella　decolorationis　S12)　iron　reduction　kinetics　in　the　surficial　tidal　marsh　sediments　of　the　Min　River　Estuary　were　compared　at　six　locations　along　the　inundation　gradient.　A　reactive　continuum　model　was　successfully　applied　to　describe　the　kinetic　results.　Along　the　inundation　gradient,　an　enhanced　tidal　inundation　frequency　towards　the　sea　resulted　in　changes　in　the　pH,　Eh,　salinity,　as　well　as　the　abundances　and　fractions　of　reactive　Fe(II)　and　Fe(III).　Significant　differences　were　observed　between　the　chemical　and　microbial　iron　reductions　among　the　six　locations.　Larger　reducible　Fe(III)　pools,　higher　initial　rates,　and　lower　mineral　heterogeneity　were　observed　in　chemical　assays　when　compared　to　microbial　assays.　The　microbial　and　chemical　reducible　Fe(III)　as　well　as　their　initial　reduction　rates　generally　decreased　along　the　inundation　gradient.　The　chemical　mineral　heterogeneity　gradually　increased　along　the　inundation　gradient,　while　the　microbial　mineral　heterogeneities　were　not　significantly　different　at　the　six　locations.　Consequently,　a　higher　iron　reduction　potential　was　observed　in　the　uplands　when　compared　to　that　in　the　lowlands.　The　result　highlights　the　role　of　tidal　hydrology　and　topography　in　iron　reduction　and　suggest　that　both　the　pool　and　mineral　heterogeneities　of　highly　reactive　Fe(III)　should　be　considered　in　iron　biogeochemical　investigations.