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Biological and chemical monitoring after pilot remediations
in the delta of the rivers
Rhine and Meuse
P.J. den Bestena,
J.F. Postmab,
J.W.M. Wegenerc,
H Keideld,
A. Klinke,
J. Molf,
C. van de Guchtea
aInstitute for inland
Water Management and Waste Water Treatment (RIZA), Ministry
of Transport, Public Works and Water Management, P.O. Box
17, 8200 AA Lelystad, The Netherlands
bAquaSense Laboratory, P.O. Box 95125, 1090MG Amsterdam, The
Netherlands
cInstitute for Environmental Studies, Vrije Universiteit Amsterdam,
De Boelelaan 1115, 1O81HV Amsterdam, The Netherlands
dBLGG P.O. Box 115, 6860 AC Oosterbeek The Netherlands
eKlink Hydrobioiogical Consultants, Boterstraat 28, 6701 CW
Wageningen, The Netherlands
fDirectorate Zuid-Holland, Rijkswaterstaat, Ministry of Transport
Public Works and Water Management, P.O. Box 556, 3000 AN Rotterdam,The
Netherlands
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Abstract
Two pilot projects were carried out to investigate the effects
of sediment remediation. One project was situated in a groyne section
of the Nieuwe Merwede, a watercourse in the Rhine delta. The second
was situated in a creek named Spijkerboor, which receives water
from the river Meuse. For both sites it was concluded earlier that
sediment pollution posed a high risk to the ecosystem. The remediations
consisted of partial excavation of the contaminated sediments, followed
by application of a clean layer of sandy material on top of the
remaining contaminated sediment. Before and at various times after
the remediation, the following investigations were carried out:
physical-chemical analyses of sediment, benthic community structure
observations, bioaccumulation measurements and sediment bioassays.
After the remediation, a new silty sediment top layer was formed
with lower contaminant levels exhibiting a lower toxicity. In the
remediated site in the Nieuwe Merwede, chironomids, oligochaetes
and nematodes reappeared within 3-7 months at normal densities,
while in the Spijkerboor recolonization by chironomids and nematodes
proceeded more slowly. After 2 years, in both the remediated sites
chironomids and nematodes were present in densities much higher
than before the remediation. Bivalves showed a low recolonization
rate in both sites. In non-remediated, polluted reference sites
also a lower sediment toxicity and a nearly comparable recovery
of the benthic community was observed, probably the result of natural
sedimentation of material with lower contaminant levels. Because
of the natural improvement of sediment quality, the net effects
of remediation were negligible in the Spijkboor. For the Nieuwe
Merwede, after 2 years still lower contaminant levels were observed
in the remediated site compared to the non-remediated site, resulting
in lower bioaccumulation in oligochaetes. However, the contaminant
levels in sediment and biota still do not meet all environmental
quality objectives. Based on the outcome of this study it is recommended
that the priority for the remedial action is made dependant on the
rate of natural covering with sediments from the rivers Rhine and
Meuse. © 2000 Elsevier Science Ltd and AEHMS. All rights reserved.
Keywords: Sediment contamination; Benthic community; Meiofauna;
Macrofauna; Bioaccumulation;
Sediment bioassays
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