Lake Medard is a recently established post-mining lake in the northwest of Czech Republic that displays significant concentrations of dissolved sulfate (dSO42-) and ferrous iron (Fe2+) in its density and redox stratified bottom water column. Siderite-buffered anoxic sediments, also rich in iron(III)-oxyhydroxides, underlie that water column characterized by limited labile organic substrates. This composition sustain a transitional redox state between nitrogenous/ferruginous and euxinic conditions. Our study focuses on the Lake Medard bottom water column elemental concentration profiles, sulfate-sulfur and -oxygen isotope compositions, bioactive ion concentrations, and planktonic microbiome data, combined with mineralogical and isotopic analyses of the upper anoxic sediments. This integrative approach reveals that the internal biogeochemical iron cycling is interlinked with that of nitrogen, sulfur and other redox sensitive metals. Minor seasonal oscillations in the monimolimnion redox potential impact mineral dissolution/(re)precipitation reactions, causing shifts in metal partitioning within anoxic sediments. Carbonate-buffered reactions appear to respond to a subsurface CO2 flux thereby influencing monimolimnial alkalinity and dissolved inorganic carbon concentrations. These hydrochemical modifications shift the sedimentary redox signals, occasionally favoring carbonate over oxyhydroxide metal-binding processes. Our findings address the fate of newly formed sedimentary oxyhydroxides in a transitional redox-stratified water column featuring ferruginous conditions without quantitative sulfate depletion to provide insights on interlinked biogeochemical processes within a concise framework