| dc.description.abstract | The recognition of the value of salt marshes and concerns over salt marsh loss has led to
the adoption of managed realignment in coastal areas. Managed realignment involves the
landward relocation of the seawall, allowing an area of agricultural land to be tidally
inundated. It is believed that managed realignment sites can act as a sink for
contaminants. However, these sites may also act as a contaminant source and pose a
risk to estuarine biota.
In this thesis, the potential for metal and herbicide release from agricultural soil and
dredged sediment in managed realignment sites was investigated by laboratory
microcosm experiments. The agricultural soil and dredged sediment were subjected to
two different salinities and drying-rewetting treatments. Results indicate the release of
metals (Cu, Ni and Zn) and herbicides (simazine, atrazine and diuron) was dependent on
their strength of binding to the soil and sediment, and complexation and competition
reactions between seawater anions, cations and the sorbed metals. The release patterns
indicated that metal and herbicide release into overlying water may continue for extended
periods of time after an initial rapid release. The total metal and herbicide loads released
into the overlying water followed the order: Cu < Zn < Ni and diuron < atrazine < simazine
with a greater release from the soil than sediment. The increase in CO2 release,
mineralisation rates, total metal and herbicide loads after drying and rewetting the soil
suggested an increase in the mineralisation of organic matter and the release of organic
matter associated metals and herbicides. Results of linear regression analyses provided
evidence that the release of the metals and herbicides as DOC-complexes was important
for soil but not for sediment. These findings indicate that there is a lower potential for
contaminant release from managed realignment sites where dredged sediments are
beneficially re-used. | en_US |
