Dissimilatory　iron　reduction　(DIR)　coupled　with　carbon　cycling　is　increasingly　being　recognized　as　an　influential　process　in　freshwater　wetland　soils　and　sediments.　The　role　of　DIR　in　organic　matter　(OM)　mineralization,　however,　is　still　largely　unknown　in　lake　sediment　environments.　In　this　study,　we　clarified　rates　and　pathways　of　OM　mineralization　in　two　shallow　lakes　with　seasonal　hydrological　connectivity　and　different　eutrophic　situations.　We　found　that　in　comparison　with　the　domination　of　DIR　(55%)　for　OM　mineralization　in　Lake　Xiaoxingkai,　the　contribution　of　methanogenesis　was　much　higher　(68%)　in　its　connected　lake　(Lake　Xingkai).　The　differences　in　rates　and　pathways　of　sediment　OM　mineralization　between　the　two　lakes　were　attributed　to　higher　concentrations　of　carbonate　associated　iron　oxides　(Fecarb)　in　Lake　Xiaoxingkai　compared　to　Lake　Xingkai　(P　=　0.002),　due　to　better　deposition　mixing,　more　contributions　of　terrigenous　detrital　materials,　and　higher　OM　content　in　Lake　Xiaoxingkai.　Results　of　structural　equation　modeling　showed　that　Fecarb　and　total　iron　content　(TFe)　regulated　25%　of　DIR　in　Lake　Xiaoxingkai　and　76%　in　Lake　Xingkai,　accompanied　by　a　negative　effect　of　TFe　on　methanogenesis　in　Lake　Xingkai.　The　relative　abundance　and　diversity　of　Fe-reducing　bacteria　were　significantly　different　between　the　two　lakes,　and　showed　a　weak　effect　on　sediment　OM　mineralization.　Our　findings　emphasize　the　role　of　iron　minerals　and　geochemical　characterizations　in　regulating　rates　and　pathways　of　OM　mineralization,　and　deepen　the　understanding　of　carbon　cycling　in　lake　sediments.　©　2022