MANGANESE NODULES
38
The footprint or spatial scale of extraction will vary with each
site. Whether a site is likely to be mined, and the extent of a
commercial mining operation, will depend on the region, nodule
distribution and density, ore grade, and topography/bathyme-
try. Initial estimates from the CCZ suggest extraction could be
on the order of several hundred square kilometres per year and
tens of thousands of square kilometres over the commercial life
of an operation (Smith
et al
. 2008). The area to be mined, com-
pared to the area that will be untouched, may be an important
consideration when developing management strategies.
There is little doubt that some amount of sediment plume will
be created by the extraction of nodules. Because of dispersal by
currents, the plume may have a larger footprint than the physical
mining area. There is also potential for such plumes to extend
into the bottom parts of the water column. Several direct mea-
surements of actual plumes generated by ploughing the sea-
floor in the CCZ showed the plumes visibly lasting up to six hours
(Bluhm 1994). Modelling indicates that dispersal and resettle-
ment rates could be very low (Rolinski
et al
. 2001) and result in
coverage of the surrounding 100 km by a layer of fine sediment
that can have a smothering effect on the benthic ecosystem,
even if the layer is less than 1 cm deep (Glover and Smith 2003).
The area affected by discharge of the waste water and fine sedi-
ments will need to be considered. Discharge plumes in the water
column will disperse with distance, and this progressive dilution
will mean there is a gradient of impact, with effects lessening as
distance from the mining site increases.
The likelihood that resedimentation could extend over a con-
siderable area adjacent to the physical operation means that
care is needed when defining conservation sites. Such areas
will have to be far enough away frommining operations to avoid
any potential “downstream” effect.
The potential extent
of impacts
3.6
In addition to the potential impacts from normal operation,
it is important to consider accidental events and natural haz-
ards. These include possible spills and oil leaks on the ves-
sel/platform that then enter the sea and leaks from the sea-
floor to vessel lifting equipment or from sea-floor equipment
(e.g., hydraulic oil leaks). Although unlikely, extreme events
– such as a ship sinking or collisions between vessels or with
marine mammals – are possible. Commercial operators and
national management agencies must reduce the risk of such
events occurring in the first instance, and they must be pre-
pared to respond if they do happen. Such precautions are
generally covered under national and/or international (in-
cluding maritime) regulations and are not detailed here.
Accidental Events and Natural Hazards
