Tidal sedimentation in the Tees estuary during the 20th century: radionuclide and magnetic evidence of pollution and sedimentary response

摘要

A series of short cores (ca. 0.5 m) were collected from the intertidal zone and reclaimed lowlands of Greatham Creek in the Tees estuary. Magnetic concentration data were combined with radionuclide chronologies based on down-core profiles of unsupported ~(210)Pb activity and ~(137)Cs activity to establish the history of estuarine pollution. The onset of metal pollution is dated to the latter part of the 19th century, peak metal concentrations date from the early 1950s, and the observed decline in metal pollution starts in the early 1980s. Radionuclide chronologies are considered unreliable in the outer part of the estuary where low ~(210)Pb activities cannot be calibrated against ~(137)Cs. In the intertidal zone, ~(137)Cs inventories correlate well with sedimentation rate and can be linked to soil erosion in the catchment rather than the marine delivery of Sellafield radionuclides. In addition, temporal offsets between reliable ~(210)Pb and ~(137)Cs chronologies in the intertidal zone can be attributed to erosion of the upper part of the sedimentary record. Both the intertidal and reclaimed regions exhibit enhanced sedimentation rates for the last 40 years. This is likely to be a response to relative sea-level rise although the impact of engineering works can also be observed in the tidal flats and saltmarshes during the last 25 years in the form of differential erosion and accelerated sedimentation.