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Understanding Dredging


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Environmental Management Framework for Deep Seabed Nodule Mining

€ 20,-


Presented during:

WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.


C. Vogt


"Deep-seabed mining of polymetallic nodules that is proposed to occur at depths around 4,000-6,000 meters, like all mining activities, has the potential to cause unacceptable environmental harm if not managed appropriately. The nodules commonly contain copper, nickel, and cobalt in addition to manganese. The deep seabed mining industry is in its infancy, with mining and environmental protection techniques in development. During mining, the two primary sources of impact are the removal of nodules from the seafloor and the discharge of return water after dewatering operations on the support vessel. Disturbance of the seafloor will instigate mixing of sediments with seawater immediately overlying the seabed. The formation of sediment plumes will occur. Effects are likely to be site-specific and will depend strongly on the seabed composition (e.g., silt vs sand), the type of technology used, the nature of the biota, and the oceanographic conditions in the area. Equipment that digs into or removes the upper layers of sediment can have an effect through direct impact of buried infauna and by compacting the substrate through the weight of the mining tools. Nodules will be separated from the sediment at the seafloor and then the nodules will be pumped to a ship where they will be separated from the seawater. The dewatering process will discharge the separated seawater back into the sea (below the light zone and possibly back to the seafloor). The amount of fine materials in the return water, which could cause a turbid plume, will depend on the amount of materials still present after the nodule separation process at the seafloor and dewatering process on board the surface vessel. The key steps in the environmental management framework are characterization of potential risks, identification of action levels, identification of mitigation for those risks, monitoring of project conditions, and adaptive management. The objective of the environmental management framework is to support the consideration of seafloor polymetallic nodule mining in a manner that enables economic, social, and environmental objectives to be achieved."

Keywords: Deep-seabed mining, DSM, nodules, environment, polymetallic, ISA, London Protocol, turbidity



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