Effects of simulated deposition of dredged material on structure of nematode assemblages – the role of contamination |
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Authors: | M Schratzberger H L Rees S E Boyd |
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Institution: | (1) University of Wales Bangor, School of Ocean Sciences, Menai Bridge, Gwynedd LL59 5EY, North Wales, Great Britain, GB;(2) The Centre for Environment, Fisheries and Aquaculture Science, Burnham Laboratory, Remembrance Avenue, Burnham-on-Crouch, Essex CM0 8HA, England Fax: 0044 (0) 1621 784989 e-mail: m.schratzberger@cefas.co.uk, GB |
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Abstract: | Certain criteria must be satisfied before a licence for the deposition of dredged material at sea in UK waters is issued.
These relate to the chemical quality of the material, the quantity to be disposed of, its nature and origin, and its predicted
impacts at the disposal site. Although chemical analyses of dredgings provide an indication of the relative degrees of contamination,
they do not provide a measure of any resultant biological effects. A laboratory experiment was therefore designed to investigate
the effects of the degree of contamination and the role of burial associated with the deposition of dredged material on the
meiofauna. Estuarine nematode assemblages were exposed to the simulated deposition of uncontaminated, oxic intertidal mud
and anoxic sediments from the Mersey and the Tees estuaries, both of which were contaminated with heavy metals. The sediments,
which differed little in terms of grain size, were deposited in two different frequencies. Nematodes showed a clear species-specific
response to the experimental treatments, depending on the frequency of deposition and the chemical quality of the deposited
material (e.g. metal and oxygen concentrations). The response of nematode assemblages was mainly determined by the deposition
frequency rather than the type of sediment or the degree of contamination. The deposition of sediment in one large dose at
the beginning of the experiment caused more severe changes in assemblage structure than the same quantity deposited in several
smaller doses. Although lower than in uncontaminated mud, relatively high migration and survival rates in the contaminated
high-frequency treatments were observed. This may have been due to reduced bioavailability of metals and the tolerance of
estuarine nematodes to both metal contamination and the deposition of small sediment volumes at regular intervals. The observed
trends demonstrate the potential of small-scale laboratory experiments for testing the quality of contaminated dredged material
at the licensing stage, i.e. prior to the issue of a disposal licence.
Received: 11 February 2000 / Accepted: 26 June 2000 |
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