Geoscience Reference
In-Depth Information
modification of channel networks (Lee et al.
1996). Restoring the physical and chemical prop-
erties of mangrove sediments, however, may
prove impossible at sites that have been used
for shrimp farming or timber harvesting, where
extreme acidification and anaerobiosis may have
occurred. If devoid of vegetation, these areas may
also be prone to rapid soil erosion and removal
of organic matter (Field 1998). Under such con-
ditions, natural reseeding or programmes of
replanting are unlikely to be successful.
The need for effective regeneration of degraded
coral reefs is equally evident both from the
perspective of disturbance-related reductions in
carbonate production and from the increased
rates of adjacent shoreline erosion that can
follow reef disturbance (see section 9.4.1).
Remedial techniques such as coral transplanta-
tion do exist, but as with mangrove replanting,
the benefits of this approach are questionable.
Edwards & Clark (1998) suggest that natural
recovery processes may be far more effective
than transplantation, with the exception of areas
that are failing to recruit juvenile corals. Even in
these cases they suggest a re-emphasis towards
transplanting slow-growing, massive corals,
which tend to be better natural recruiters than
fast-growing branched corals. Massive corals
are also less susceptible to the effects of coral
bleaching (McClanahan 2000). At best, trans-
plantation is only likely to be effective on a
localized scale, so that resources may be better
directed at managing or mitigating the causes of
degradation (Bellwood et al. 2004).
ant inputs can often be identified, some being
sourced from the coastal fringe, but many
linked to activities that occur upstream within
coastal catchments. The diverse range of bodies
with responsibilities to regulate these different,
but linked environments can cause significant
management problems.
The central Great Barrier Reef (GBR) provides
an interesting perspective on the uncertainties
that exist in relation to terrigenous impacts on
nearshore marine environments, and the issues
of coastal and marine management. There have,
for example, been suggestions of increasing sedi-
ment runoff and, associated with this, increased
nutrient and contaminant (pesticide) levels,
linked to agricultural activities in the catchment
areas (Haynes & Johnson 2000). Although sedi-
ment input rates do appear to have increased,
there is conflicting evidence about whether or
not this is having a detrimental effect on the
marine environment and on the coral reefs in
particular, because most fluvially derived sedi-
ments accumulate only along nearshore areas of
the shelf (Larcombe & Carter 2004 - see Case
Study 9.1). The GBR region, however, does high-
light the important linkages that exist between
coastal environments and river catchments.
Management of the GBR is primarily under the
jurisdiction of the Great Barrier Reef Marine
Park Authority (GBRMPA). Although the GBR
itself is widely cited as an example of good
marine management practice, the GBRMPA has
little influence over managing the catchments
that feed onto the shelf. Instead, current man-
agement of agricultural activities and hence
runoff are under a voluntary code of practice.
Given the uncertainties about the actual impacts
of terrestrial sediment inputs on the GBR, the
effect of changing land-use practices, in terms
of the marine environment, seem unclear. The
region, however, emphasizes the potential bene-
fits of integrating both coastal and catchment
management schemes.
Remediation of contaminated sediments pre-
sents an additional challenge and one that is
important given the potential for sediments to
both store and episodically re-release contamin-
ants (see section 9.4.4). In the case of oil con-
tamination, chemical dispersants traditionally
9.5.3 Managing sediment contaminants
As outlined in section 9.4, nearshore sediments
in general, and mangrove sediments in par-
ticular, have considerable potential to trap a
wide range of contaminants relating to indus-
trial, urban and agricultural discharges. In
mangroves, these contaminants, if present
in sufficient concentrations, can lead to tree
defoliation, seedling mutations, reduced species
diversity and mangrove die-back (Ellison &
Farnsworth 1996), and in coral reefs to disease,
and reduced growth and reproductive potential.
In many coastal systems a range of contamin-
