The magnetic record of particulate pollution in a saltmarsh, Dee Estuary, UK

Abstract

In the sediments of a rapidly accreting salt marsh at the head of the Dee Estuary (northwest England) magnetic measurements reveal a strong and persistent signal which can be related to the historical effluent discharges of a large iron and steel works. The iron oxide content of the pipeline emissions from the works permits their detection by rapid and simple measurements of the weak remanent magnetization of sediments. The spatial extent of contamination of the saltings has been determined. A clear distance-decay effect from the point source has been observed in those parts of the saltings which accumulated during the period of strongest emissions from the plant. Furthermore, down core, a marked and spatially consistent 'spiked' magnetic profile has been recorded. This distinctive pattern of changes in magnetic concentration and grain size mirrors the past activities and discharges of the works. This supposition is corroborated by a supporting chronology based on the record of 137CS emissions from the Sellafield nuclear fuel reprocessing plant and by historical maps of the intertidal area. Thus, the magnetic properties of these salt marsh monoliths record spatial and temporal variations in discharges from the works to the saltings. In addition, they provide unique stratigraphic markers which can assist in the determination of net sediment accretion rates and the reconstruction of the evolution of the saltmarsh.