“…Fe(II)-containing minerals are widely observed in sediments collected from subsurface aquifers, ,, a floodplain adjacent to the Yangtze River, the Pearl River watershed, and tundra near Toolik Lake . Ferrous iron in these sediments has been associated with individual RIM, including mackinawite, siderite, , ankerite, biotite, , montmorillonite, chlorite, , and illite, , and has been linked to the presence of dissimilatory iron and sulfate reducing bacteria that promote Fe(III)-(oxyhydr)oxide mineral and aqueous sulfate reduction. , Anoxic sediments containing RIM can become exposed to O 2 and produce reactive oxygen species. The former can occur, for example, due to temporal and spatial fluctuations of the groundwater table driven by hydrological dynamics (e.g., injection or extraction of groundwater, , precipitation or drought conditions, rising and falling levels of rivers connected to aquifers , ), flooding or drying in agricultural fields, and thermocline disruptions in surface waters .…”