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4.2. Extrapolation of impact experiments to large-scale mining
A comparative study of the impact experiments conducted by different
groups in the Pacific and Indian oceans has shown the following.
1. The mechanism for disturbing the seabed differed between the
DISCOL (Disturbance and Recolonization) and other benthic impact
experiments (BIEs). In DISCOL, the emphasis was on ploughing the
seabed, while the other BIE projects concentrated on sediment
resuspension. Both operations are based on tow-type instruments
and are complimentary to each other in their actual mining scenario.
Combining these approaches could afford a more realistic means of
studying the potential effects on the seafloor.
2. The duration of these experiments, two weeks (DISCOL) or several
tens of hours (18-88 hours for the BIEs), is much smaller than any
kind of large-scale mining operation, which is expected to last for
about 300 days per year 9 . The distances covered during these
experiments (33-141 kilometres) are also quite small. Similarly, the
volume of sediment recovered during different experiments,
calculated as 0.77 m 3 /minute (NOAA-BIE), 1.17 m 3 /min (JET), 1.4
m 3 /min (IOM-BIE) and 1.35 m 3 /min (INDEX), ranges between 2 and
3.7 percent 10 of the estimated volume of sediment (54,000 m 3 /day,
i.e. 37.5 m 3 /min) to be recovered during a commercial mining
operation. Hence, all these experiments can be considered as
microscale experiments in terms of sediment resuspension. In future,
it may be advisable to conduct a relatively larger-scale experiment to
study the impacts of such a disturbance on the benthic ecosystem.
None of the results from impact studies can be applied to predict
the effects of large-scale mining for the following reasons:
a. The size of the site selected for impact assessment for a pilotmining
test will be a few orders smaller than that of commercial
mining.
b. The volume of resuspended sediment and the depth at which it
will be released may not be the same as in large-scale mining.
c. The capability of the nodule collector to penetrate into the
seafloor and discharge the slurry into the water column will not
be the same.
INTERNATIONAL SEABED AUTHORITY 481