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within an area extending several tens of metres beyond the discharge point.
Cool water discharged at the surface layer is carried by the northward
current but at a lower depth.
2.5.2. Enrichment experiment
As part of the environmental impact research for manganese nodule
mining, experiments were carried out to determine the impact of the mining
effluent on phytoplankton. These experiments was conducted to determine
the effects of introducing deep-sea water, which contains high nutrient
concentrations, on dominant pico- and nanoplankton.
Results of the experiments showed that the addition of deep water
could cause an increase in chlorophyll a and changes in the composition of
these communities. In experiments where the concentration of bottom
water was low, cell-number maxima were attained in a shorter period. In
contrast, in experiments with high concentrations of bottom water, it took
more days to reach the maximum and the values were higher than those in
other experiments with lower concentration (figure 7). However, at higher
concentrations (50% surface seawater and 50% bottom water),
microflagellates increased with decreasing nitrate and nitrite
concentrations, and Bacillariophyceae showed an increase at lower
concentrations. In all the experiments the daily growth rate of
bacillariophyceans increased with increasing initial concentrations, though
cyanobacteria and microflagellates showed no significant correlation with
bottom-water concentrations.
These results suggest that the concentrations of nitrate and nitrite
can influence succession of phytoplankton communities.
3. Benthic Environmental Study
The field study of the benthic environment, which included both
baseline and impact assessment research (the latter labelled JET: Japan
Deep-Sea Impact Experiment), was performed in the western part of the
exclusive Japanese claim area in the Central Pacific Ocean (figure 8). The
purpose of JET was to evaluate the effect of artificial rapid sediment
deposition (=disturbance), which was supposed to occur during commercial
mining. This experiment consisted of four field studies, as follows:
JET 1: the field study conducted before the disturbance;
JET 2: the field study conducted immediately after the disturbance;
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