Geoscience Reference
In-Depth Information
Discovery
Bay
(a)
(b)
> 95%
90.0 -94.9%
85.0 -89.9%
80.0 -84.9%
75.0 -79.9%
<75.0%
Carbonate content
Reef crest
N
JAMAICA
20 m
10 m
5 m
5 m
5 m
10 m
20 m
30 m
50 m
40 m
Bauxite loading
terminal
500 m
(c)
Fe vs carbonate
100
r
2
= 0.811
90
80
70
Fig. 9.20
(a) Location of Discovery Bay on the north coast
of Jamaica, with the bauxite loading terminal situated in the
south-west corner of the bay. (b) Contour map showing
variations in carbonate content of sediments. Lowest levels
occur near the loading terminal and are closely correlated with
levels of iron (c), zinc and manganese. (Adapted from Perry &
Taylor 2004.)
60
50
40
0
5000
10000
15000
Fe (
µ
g g
−
1
)
Significant ecological impacts on mangroves
and corals also can be attributed to oil con-
tamination. In large part, impacts relate to the
buoyant nature of spilled oil, which is thus
easily transported into intertidal settings by
winds and currents. In mangroves, ecological
impacts relate primarily to smothering of aerial
roots and pneumatophores, leading to oxygen
deficiency and rapid mortality of mangrove
trees (Levings & Garrity 1994). There also may
be impacts on mangrove propagule vitality
(Duke & Watkinson 2002). In reef settings, oil
may reduce coral growth and modify reproduc-
tive rates (Guzmán et al. 1994). The incorpora-
tion of oil residues into shallow marine and
intertidal sediments is strongly site-dependent
and is influenced by the rate of hydrocarbon
weathering (Munoz et al. 1997) and the tidal
regime, which influences the spatial extent of oil
distribution (Lewis 1983). It is clear, however,
that mangrove sediments have the potential to
act as temporary sinks for oil residues. This is
attributed in part to the anaerobic nature of the
sediments, which inhibits microbial degradation
of hydrocarbons, and to the rapid incorporation
of oil into the sediments via burrow networks.
Trapping is also aided by the ability of hydro-
carbon residues to bond tightly to fine-grained
suspended sediments (Ke et al. 2003). The long-
term persistence of oil residues in mangrove
systems is discussed by Burns et al. (1993),
who also illustrate the potential for periodic or
pulsed phases of oil residue release as sediments
are leached during runoff or storm-wave-related
erosion (Case Study 9.4).
9.4.5 Multiple-cause disturbances and changing
patterns of sedimentation
Particularly in the case of coral reefs, it is
often difficult to isolate the individual factors
that induce community decline and shifts in
