Environmental Engineering Reference
In-Depth Information
TABLE 8.7
Comparison of Heavy Metal Concentrations in Sediments with and
without Eelgrass (Seto Inland Sea, Japan)
Heavy Metal (mg/kg)
Sampling Point
Cu
Pb
Zn
A
With eelgrass
11
20
76
B
Without eelgrass
13
10
83
C
With eelgrass
11
25
69
D
Without eelgrass
14
130
90
E
With eelgrass
15
17
77
F
With eelgrass
16
18
82
G
Without eelgrass
27
17
110
H
With eelgrass
17
18
83
Average with eelgrass
14
19.6
77.4
Average without eelgrass
18
52.3
94.3
the breeding ground and habitat for all kinds of marine animals including crabs, scallops,
and other kinds of shellish. They not only serve to foster and stabilize the benthic habitats,
but they also have the potential for phytoremediation. Eelgrass can absorb trace metals
and organotins (Brix and Lyngby, 1982; Fransois et al., 1989).
Table 8.7 gives a comparison of concentrations of various heavy metals in sediments
with and without eelgrass. The sediments that were taken from a small eelgrass sward at
an estuary of Kasaoka Bay in Seto Inland Sea, Japan, consisted of a number of small com-
munities, with bare parts between the communities. The total area of the eelgrass sward
was 1491 m 2 . The sampling points from A to H were located in the bare parts and com-
munities. The results show that the sediments with eelgrass contain a lesser amount of
heavy metals—most likely attributed to heavy metal absorption (uptake) by the eelgrass.
Since eelgrass grows from spring to summer, and their dead leaves drift upward to the
sea surface at the end of their growing season, collection of the dead leaves can be sim-
ply implemented. This means that if eelgrass is used for phytoremediation, the absorbed
heavy metals can be harvested with the dead seagrass leaves.
Reclamation and other near-shore industrial activities can negatively impact the coastal
habitat, particularly on the seagrass beds that form the seaweed ields. Reduction of sea-
weed ields not only decreases the habitat of marine living things but will also result in a
marked decrease in the haul of inshore ish. For example, in Japan, approximately 6000 ha
of seaweed ield have disappeared since 1978, and about one third of this is due to the
impact of reclamation projects.
8.7 Sea Disposal of Waste
Dumping or discharging land-based industrial waste into the sea is essentially prohibited—
with the burden of responsibility resting on the waste generator to ensure that any waste
material entering the sea must be nontoxic and nonhazardous. Section 8.2 has discussed
the strict prohibitions articulated in the London Convention and Protocols. Since many
countries and jurisdictions with restricted land areas do not have suficient land space for
 
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