A review of sediment contamination by trace metals in the Humber catchment and estuary, and the implications for future estuary water quality

This paper reviews what is presently known about sediment contamination in the macro-tidal Humber estuary on the east coast of the UK, with particular reference to the trace elements arsenic, copper, lead and zinc. The Humber is a post-industrial estuary, with an industrial and mining legacy of contaminated sediments throughout the river catchment. Surface and near-surface sediments in the estuary also show significant contamination of trace metals over background values. Inputs of dissolved and particulate trace elements to the estuary from the rivers are reviewed, and atmospheric deposition to the catchment and estuary calculated as a potential additional source of contamination. The necessity of maintaining the sediment balance within the estuary means that contaminated sediments dredged from the estuary harbours are deposited to other sites within the estuary, rather than being removed. Trace metal concentrations in recent dredged sediments, and sediments from the period of peak contamination in the 1970s. are compared with background values. Current inputs to the estuary from point sources, and trends over the last decade are considered. Our calculation of the current depositional fluxes of trace metals to the estuary intertidal sediments, and comparison with the inputs, reveals that the estuary sediments are today capable of storing 55-97% of the input load of As, 15-27% of the Cu, 17-50% of the Pb and 11-12% of the Zn annually. Sediment quality in the estuary is currently far from its 'background' state with respect to trace metals. This has implications for the future water and sediment quality of the Humber under the terms of the EU Water Framework Directive. One management option being considered to improve sea defences in the estuary, managed realignment, may also act to dilute contaminated sediments in the estuary, and thereby to improve future water quality. We look at the effect on sediment contaminant storage of three possible future managed realignment scenarios. (C) 2004 Elsevier Ltd. All rights reserved.