The results of this study revealed that the sediments of Laizhou
Bay were contaminated by Cu and As, but the concentrations of
these metals were not sufficiently elevated to ecologically damage
the benthic community. Furthermore, metals of potential concern
with moderate adverse effect in potential have both natural and
anthropogenic sources. Despite the increase in anthropogenic metals
delivered to the surveyed region, a trend of metal contamination
mitigation was inferred from the decadal variation of
sediment metal concentrations. This phenomenon can be
explained by the sediment transport mode and flux variation as
well as the coarser grain size resulting from soil conservation
and reservoir construction in the watershed of the Huanghe River.
Therefore, adverse effect of metals was minor-than-expected since
far from extreme exposure levels were found.
This study also suggests that the differences in benthic community
structure among groups reduced via NMDS may be attributed
to environmental stressors other than toxic metals that were not
analyzed in the present study. Physical–chemical habitat disturbance
resulting from riverine and coastal stressors was further
indicated as a possible responsible factor, demonstrating the complexity
of Laizhou Bay under multiple environmental changes. In
addition, the thrive of Polychaeta (C. capitata in particular) on the
south bank of the Laizhou Bay raises alarm about the health status
of this marine ecosystem. By integrating chemical and biological
evidence, sediment quality was preliminarily assessed. The results
showed that impaired sediments are mainly found in the central
and northern portions of Laizhou Bay, where higher levels of sediment
contaminants and less diverse benthic communities occur.
The present study also illustrated that evaluation the adverse effect
of sediment toxic metal need to integrate the key information provided
by benthic community structure, which provide ecologically
significance to the metals.
Considering that this study was carried out in an area subject to
continuous pressures due to dramatic variations in water and sediment
fluxes from the Huanghe River and increasing anthropogenic
contamination, the limited number of sampling locations as well as
the paucity of laboratory toxicity testing and biota residual analysis,
may undermine the reliability of relationships analysis and
sediment quality. Therefore, further intensive studies should be
continually conducted