Geoscience Reference
In-Depth Information
Case Fig. 7.3
Eroding sediment of the Northwick Formation, Northwick Warth, Severn estuary. The erosion of this marsh,
accreting since the 1930s, is now contributing stored contaminants back in to the water body. (Data from French 1996.)
marsh investigated here is only a small part of the salt marsh resource of the estuary. The two
banks of the Severn estuary combined cover a distance of over 400 km, much of which is salt
marsh. Hence, the release of material from these sources is potentially large.
Relevant reading
French, P.W. (1996) Long-term variability of copper, lead and zinc in salt marsh sediments of the Severn
Estuary.
Mangroves and Saltmarshes
1
(1), 5968.
dominated. This would have represented the first
major stability change. Managed realignment
reintroduces brackish water to these areas,
increasing the saturation of the soils and causing
further remobilization of many pollutants. The
processes by which remobilization occurs are
diverse and include metal transformation by pro-
cesses such as methylation, change of chemical
phase due to the changing oxygen availability,
salinity, redox, bioturbation and acidity/alkalinity.
Bryan & Langstone (1992) provide a full review
of these processes, and Emmerson et al. (2000)
demonstrate the role of changing acidity and
chlorinity in the release of sediment-bound metals
in a field-based situation at Orplands, Essex, UK.
Blackwell et al. (2004) look at the immediate
post-breaching change in the Torridge estuary,
Devon, UK.
Problems with mobilization can become severe
if levels of a particular contaminant are pres-
ent in sediments in high concentrations. This
may be the case where sediments are associated
