A 100-y geochemical record preserved in the sediments of a Mississippi oxbow lake yields evidence that chemicals entering from agricultural fields are only temporarily sequestered in the riparian fringe prior to active removal and transport to open water. Elevated concentrations of Pb and As, corresponding to peak historical use of lead arsenate pesticide, are clearly identified in open water sediment cores, but are absent in cores from the riparian fringe; P concentrations are also significantly higher in the open water cores than in the riparian fringe. A conceptual model is proposed where elements initially deposited in the riparian zone are seasonally remobilized by release from decomposing litter, and through uptake by wetland trees that return elements to the litter through leaf senescence. Within the riparian zone, seasonal remobilization eventually diffuses or eliminates the historical record. Elements that reach and settle out in the open water environment are sequestered and an historical geochemical record is preserved.