Heavy metal contamination and mixing processes in sediments from the Humber Estuary, Eastern England

The geochemical properties of cores collected from mud flat and salt marsh environments in the Humber Estuary were investigated. A total of 10 cores were collected along a shore-normal transect on the northern bank of the estuary, near Skeffling. Major and trace element concentrations were determined for each core. The vertical distributions of210Pb and137Cs were also examined to provide a measure of the rate of sediment accumulation. Surface intertidal sediments show elevated concentrations of a range of trace and major elements, including Pb, Zn, Cu, Al, Mn and Fe. Concentrations were higher in the upper mud flats and salt marsh where sediment grain size is finer. Dating of salt marsh sediments indicated a local sediment accretion rate of 0·4 cm yr−1. The early-diagenetic remobilization of heavy metals has apparently been limited, and the salt marsh sediments provide a (time-integrated) record of historical pollutant inputs. Heavy metal fluxes have been calculated from the salt marsh sediments and are broadly comparable with other industrialized and semi-industrialized estuaries. Cu, Pb and Zn inputs to the Skeffling area peaked in the mid-20th century, while Ti, Al and Fe, which are discharged into the Humber from two Tioxide-processing facilities, are only slightly enriched in these sediments. On the mud flats, local mixing, resuspension and erosion has resulted in correlatable sedimentary horizons interspersed with mixed sediment layers. Consequently, the vertical distribution of heavy metals in these mud flats is relatively erratic, and the mud flat sediments are unsuitable for studying historical pollution trends.