Expanding　worldwide　aquaculture　has　greatly　increased　greenhouse　gas　emissions;　however,　the　underlying　microbial　mechanisms　are　poorly　understood.　In　particular,　the　role　of　ferric　iron　[Fe(III)]　(hydro)oxides　in　carbon　mineralization　in　aquaculture　pond　sediments　remains　unclear.　Here,　we　studied　the　rates　of　microbial　Fe(III)　reduction,　sulfate　reduction,　methanogenesis,　and　carbon　mineralization　in　aquaculture　shrimp　(Litopenaeus　vannamei)　ponds　of　various　salinities　before,　during,　and　after　shrimp　farming　in　subtropical　estuaries　in　southeast　China.　Sediment　samples　(0-10　cm)　were　collected　to　investigate　the　content　of　iron　species,　characteristics　of　organic　matter,　and　abundance　of　Geobacter,　a　proxy　of　iron　reducers.　Overall,　Fe(III)　reduction　(46.1%　19.1%)　dominated　carbon　mineralization,　followed　by　sulfate　reduction　(39.6%　16.8%)　and　methanogenesis　(1.5%　1.1%).　Microbial　Fe(III)　reduction　contributed　more　to　carbon　mineralization　during　farming　than　before　and　after　farming.　This　enhancement　in　Fe(III)　reduction　is　attributed　to　a　significant　increase　in　Fe(III)　content　during　farming.　Additionally,　the　contributions　of　microbial　Fe(III)　reduction　to　carbon　mineralization　were　lower　in　the　high-salinity　ponds　than　in　the　low-salinity　ponds　due　to　the　suppression　of　sulfate　reduction,　abiotic　Fe(III)　reduction　by　sulfides,　and　lower　oxidation-reduction　potential.　Our　findings　demonstrate　that　microbial　Fe(III)　reduction　plays　a　significant　role　in　carbon　mineralization　in　aquaculture　pond　sediments.　Future　carbon　flux　prediction　models　of　aquaculture　pond　systems　should　fully　integrate　microbial　Fe(III)　reduction.　Plain　Language　Summary　The　expanding　global　aquaculture　industry　has　greatly　increased　the　carbon　mineralization　potential　(i.e.,　production　of　carbon　dioxide　and　methane).　Carbon　mineralization　is　mediated　by　various　types　of　microbial　respiration,　including　iron　reduction,　sulfate　reduction,　and　methanogenesis.　Aquatic　sediments　are　enriched　with　iron　oxides;　however,　the　contribution　of　microbial　iron　reduction　to　carbon　mineralization　in　the　aquaculture　sediments　is　poorly　understood.　Here,　we　studied　the　rates　and　pathways　of　carbon　mineralization　in　aquaculture　shrimp　(Litopenaeus　vannamei)　ponds　of　varying　salinities　before,　during,　and　after　shrimp　farming　in　subtropical　estuaries　in　southeast　China.　Our　results　show　that　microbial　iron　reduction　has　a　larger　contribution　to　carbon　mineralization　during　farming　than　before　and　after　farming.　In　addition,　the　contributions　of　microbial　iron　reduction　to　carbon　mineralization　were　lower　in　the　high-salinity　ponds　than　in　the　low-salinity　ponds.　Overall,　microbial　iron　reduction　contributed　approximately　46%　to　carbon　mineralization,　followed　by　sulfate　reduction　(approximately　40%)　and　methanogenesis　(approximately　2%).　Our　findings　demonstrate　that　microbial　iron　reduction　plays　a　significant　role　in　carbon　mineralization　in　aquaculture　pond　sediments.　Microbial　Fe(III)　reduction　should　be　involved　in　future　carbon　flux　prediction　models　of　aquaculture　pond　systems.