Seasonal reproduction and preservation of foraminifera were monitored for three years at Bombay Hook National Wildlife Refuge (Smyrna, DE). Cluster analysis of “seasonally artificially time-averaged” (SATA) assemblages indicates that assemblages reflect the most recent test inputs, and that test inputs record subtle variations in porewater chemistry related to rates of sulfate reduction, pyrite oxidation, and vertical differentiation of geochemical gradients. Changes in geochemical gradients are caused by interannual variation of rainfall: more rainfall damps pyrite oxidation and weakens geochemical gradients, whereas less rainfall allows more pyrite oxidation and strengthens vertical gradients. Geochemical overprinting of assemblages related to rainfall tended to occur during the summer and early fall. Therefore, as assemblages pass into the historical layer, they may have a “memory” of the most recent test inputs and environmental conditions.