Appraisal of contaminants in sediments of the Inner Bristol Channel and Severn Estuary

Abstract

In the inner Bristol Channel and Severn Estuary, most contaminated stations were in muddy, depositional areas of the estuary, particularly along the Welsh coast between the Rivers Taff and Usk, and also on the English coast between Avonmouth and Severn Beach. Some deeper areas, dominated by sand and mixed sediments, also showed contaminant concentrations in excess of those predicted from sediment texture, organic matter, and aluminium or iron concentrations. Concentrations of lead, copper, chromium, nickel and zinc have decreased in the muddy sediments since the 1970s, but only lead has decreased in sand. With the exception of zinc, which is high in the Severn, trace element concentrations were comparable to those from other British estuaries. Landward of the proposed barrage, contaminants are associated with the sub-estuaries and muddy areas at their confluence with the main estuary. Post-barrage effects on contaminants will be focused in these muddy areas. However, fine sediment deposition on what are now sandy areas would increase their contaminant burden unless calcium build-up from the resulting molluscan fauna has the antagonistic effect of contaminant dilution in the sediment.