Seagrass-Watch Magazine Issue 47 - March 2013 | Page 15

PIANC Working Group 157

KT

A new PIANC working group (157) on ‘Environmental Aspects of Dredging and Port and
Waterway Construction around coastal plant habitats’ was launched in February 2012 to
review and summarise “best management” practices for dredging operations, and
waterway and port construction near coastal plant habitats, such as seagrass meadows,
macroalgal communities (e.g. kelp), mangroves and salt marshes. The group comprises
experts from around the world, including scientists, consultants, dredging experts and port
authorities. The best management practice guidelines, aimed to minimise damage to
coastal plant habitats, will become available in early 2014
PIANC, established in 1885, is the global organisation providing guidance for sustainable
waterborne transport infrastructure for ports and waterways. PIANC is the forum where
professionals around the world join forces to provide expert advice on cost effective,
reliable and sustainable infrastructure to facilitate the growth of waterborne transport.
PIANC continues to be the leading partner for government and the private sector in the
design, development and maintenance of ports, waterways and coastal areas.

For more information: www.pianc.org/downloads/envicom/tor%20157-EnviComCoastalplanthabitats-final.pdf
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Controlled shading experiments of seagrasses to study
their response to reduced light due to dredging plumes.

So, not all seagrasses are equally sensitive to the effects of
dredging. Larger, slow-growing climax species with substantial
energy reserves in their below-ground rhizomes (e.g. Posidonia or
Thalassodendron) show greater resilience than smaller, fastgrowing opportunistic species (e.g. Halophila spp.), but the latter
display much faster post-dredging recovery (often from natural in
situ seedbanks) as long as water-quality conditions return to the
typical background range.
Monitoring and detecting impacts from dredging operations to
seagrass meadows can be challenging, especially in areas that are
naturally subject to frequent storms and floods and consequently
display major seasonal or year-to-year changes in abundance
and distribution.
Environmental impact assessment prior to dredging allows the
identification of alternative designs to avoid or mitigate any
impact. If some impact is unavoidable, then adoption and
enforcement of effective and tight control measures,
accompanied by monitoring before, during and after dredging,
can manage the risks of adverse impacts on seagrasses from
dredging down to an acceptable minimum. Mitigating measures
that have been applied during dredging operations near
seagrasses include minimisation of spill, overflow and leakage

from the dredges and barges; judicious selection of dredging
equipment; seasonal or tidal restrictions; turbidity limits triggering
specific management responses; and reactive (feedback)
monitoring. These measures can be costly but avoid the likely
greater costs associated with loss of ecological functions and the
costs of seagrass meadow restoration.
The good news is that such “best management” practices seem
to have been effective in preventing or minimising impacts to
seagrasses in many recent dredging projects, in particular around
Australia and in the USA.

Further reading
Erftemeijer, PLA and Lewis III, RR (2006). Environmental impacts of dredging on seagrasses: a review. Mar. Poll. Bull.
52(12): 1553–1572.

MARCH 2013

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