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Among the chemical parameters, the data sets for calcium
carbonate, TOC and TN had been recognised as suitable indicators for
sediment deposition. Radioisotopes Th-234 and Pb-210 were indicators for
the recovery process and bioturbation rate. Among the physical
parameters, deep-sea currents had been measured to develop a numerical
model study, while sedimentation rates in the natural environment had
been used for background description as a basis for estimating
resedimentation. Among geological factors, grain-size measurements had
been used for devising a numerical model, and penetration and shear
strength would be utilised for future collector designs.
For the biological study, the abundance of sedimentary bacteria,
meiobenthos, macrobenthos and megabenthos had been investigated to
evaluate the effect of artificial rapid deposition. Different responses to the
disturbance had been observed within those fauna, strongly demonstrating
the importance of the biological studies.
Explaining the strategy of sampling and observation, Mr. Fukushima
said that random sampling of sediments had been conducted using
multiple corers, while line-transect observations had been carried out by
video at various sites (see figure 10 above). In the pre-disturbance phase,
sampling locations had been selected at random from an area extending
100 m from the disturbance site, permitting statistical estimation of natural
environmental conditions. Monitoring studies immediately after the
disturbance had been done in JET 2. The sampling stations had been
decided according to a modified line-transect method at distances of 25, 50
and 100 m from the tow tracks. Sediment samples during JET 3 and 4 –
one and two years, respectively, after the disturbance – had been collected
at random from areas broadly categorised as heavy deposition, medium
deposition, light deposition and no deposition areas.
During the video observation, to maintain a 3-m wide coverage area
the researchers had tried to tow the assembly at a constant distance of
about 3 m above the sea bottom. Observations had been made along lines
transecting the deposition and no deposition areas. For quantitative output
of the megabenthos study several hectares had to be observed, so that five
transect lines had been established.
To understand the characteristics of the sediment and the benthic
communities, it was important to determine optimum methods of sampling
and sample processing. To this end, a methodological study had been
conducted beginning in 1991.
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