standardization of environmental data and information - International ...

Asked whether the impact would be different if the discharge
occurred in deep water rather than at the surface, he said he thought the
consensus at the Sanya Workshop had been that releases should be below
1000 m, in other words below the oxygen-minimum layer and the whole
mesopelagic level. In that case, surface effects would be limited to some
accidental discharges and overflows, while the primary impacts would hit
the bathypelagic plankton as the sediment went down through the water
column. Presumably, the impact would affect an area of the ocean that was
a lot less sensitive to human concerns. While he recommended minimising
the impact on the surface ocean, some discharge would be almost certain,
hence the need at least to consider what the potential impacts could be
and look at them in relation to the amount of discharge.
The participant who raised this question remarked that, if the
International Seabed Authority were to set a tailing discharge depth at
perhaps 1000-1200 m from the surface, the consortia could save a lot of
money by not having to provide information about the plankton community
in the upper 1200 m or to monitor that area during mining. He
acknowledged that some information might still be needed on unavoidable
impacts from the mining ship or platform – for example, noise in the water
that might affect mammals. Another participant thought this might be a
good idea for impact monitoring but baseline monitoring should cover the
entire water column.
One participant said he had made a fast computation according to
which a collector 16 m wide, travelling at 2 kilometres an hour at a depth of
4500 m, would move between 1000 and 2000 m³ of water an hour, which
would be diluted in 15 million m³. (Another speaker observed that the
amount of discharged water would be about equal to the volume of the
mining vessel.) As an engineer rather than a scientist, it seemed to him
that 2 parts out of 15,000 implied a very diluted effect in the water column.
On the bottom, the collector would kill everything; there was no way to be
gentle with the bottom. However, because energy use for the collection
process was one of the major problems faced by engineers, the aim was to
avoid moving what was not useful. Most of the sediment debris would be
washed away at the bottom, so that mostly water and nodules would be
brought up. If it were possible, only nodules, pure and clean, would be
lifted.
Koslow was asked how disturbances and mortality at the bottom
would affect animals in the water column or at the surface. He replied that
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INTERNATIONAL SEABED AUTHORITY