Manganese nodule mining

Manganese nodule mining

Marine Pollution Bulletin Manganese Nodule Mining level whereby we can stipulate exactly what needs to be looked at to monitor the impact of mangane...

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Marine Pollution Bulletin

Manganese Nodule Mining

level whereby we can stipulate exactly what needs to be looked at to monitor the impact of manganese nodules mining, we will know the most vulnerable components of the community, and perhaps most importantly, we will have a clear understanding of how this ecosystem functions. GARETH DAVIES

Whilst the vagaries of the world mineral markets at present have slowed down the development of manganese nodule mining as a commercial enterprise, scientists and legislators are taking advantage of this respite to establish a sound package for the protection of the deep-sea environment which will take the brunt of any such operation. Along with building a legal framework within which the operators can work, a large effort is concerned with assessing the impact of mining upon the biota at the The ability of marsh plants such as the reed, Phragmites. potential sites. Because of the lack of actual mining operations to to transfer oxygen from the atmosphere to their rhizomes monitor, research on impact assessment is based on at a rapid rate is being used for the aerobic treatment of understanding basic benthic and pelagic processes in the sewage. According to a recent report in ENDS (No. 125. deep-sea and using what are thought to be analogous June 1985) such a system, designed by Reinhold stimuli to test hypotheses about community and individ- Kickuth, Professor of Ecochemistry at Hessen Univerual organism reaction. Along with studying the reaction sity, is already operational in West Germany. The system. of the ecosystem to mining, a basic description of the known as Root Zone Biotechnology (RZB) sewage environment and its inhabitants is being completed as far treatment, requires relatively modest engineering works consisting of the excavation of a gently sloping basin 1as is possible. When commercial mining does start it is envisaged 2 m deep, sealed with clay or bentonite to prevent water that the collecting devices will consume 20 m wide loss. The basin is filled with a relatively non-porous soil swathes of the sea bed to a depth of 10 cm. An estimated mixture with a capacity to remove effluent constituents 60% of the mining area will be tracked over with a nodule such as phosphorous and heavy, metals. The unit is then p!ck-up efficiency of around 70%. It is planned to dis- equipped with an effluent distributor and a collection charge most of the sediment taken up with the nodules at pump, and the soil planted with reeds. It has been shown by Professor Kickuth that the soil the sea bed. This is to ensure minimal dispersal which is interstitial spaces around the rhizomes of the reeds conhighly desirable for both economic and environmental tain up to 100 times as many types of micro-organisms as reasons. are found in adjacent soil. The rhizomes apparently This discharge of sediment is known as the benthic create a hydraulic pathway along which effluents can plume. Along with the direct destruction of the sea bed flow bringing them into contact with the enhanced by the mining device, the major impact from mining is microbial community. The use of a relatively non-porous expected to come from the settling of this plume over the soil ensures that liquids discharged into it flow along the benthos. Various projects currently looking at the problems rhizomes. This RZB system has been in operation in Othfresen, associated with deep-sea nodule mining were discussed recently at a deep-sea symposium in Hamburg. The W. Germany for 10 years and has been shown to be results of a study which returned to one of the pilot test capable of reducing a BOD of 500-700 mg 1-~ for mining sites in the Pacific, 5 years after the test had incoming sewage to 5-15 mg 1-~ at the outfall. Levels of occurred, are at present being assessed. It seems that as nitrogen are reduced by 90%, and 99% of the phosfar as the macrofauna are concerned there is no signifi- phorous is removed by soil reaction. The original treatcant difference between the community adjacent to the ment plant was about 1 ha and could cope with screened mining site and that in control areas. The only indication and degritted raw sewage from a nearby population of that there had been a possible effect at one time, was that 2700. The first British applications of RZB are likely by the the community structure was more homogeneous near the mining site. This possibly indicates that a recovery end of this year. The system is to be marketed in Britain community had been sampled, which had almost reached by Oceans International, a Bradford company that its climax apart from the minor spatial heterogeneity so believes that RZB has a great potential for treating not characteristic of an established community. Efforts to only sewage, but also industrial effluent, landfill leachate simulate the expected mining impact in a similar but and contaminated land. more accessible region than the mining site, are also underway. There is a hope that in the near future an artifical benthic plume will be generated, and that the impact of this and recovery of the benthos effected will be moniUSA tored in far greater detail than has previously been possible. Also, small scale biogenic disturbances, such as The US Environmental Protection Agency (EPA) has caused by burrowing animals are being studied to look at accused Texaco Inc. and Atlantic Richfield Co. (ARCO) the rates of sediment turnover and recolonization of of making excessive discharges from 32 offshore oil rigs in the Gulf of Mexico. Texaco, based in New York, is barren sediment in the deep-sea. Through these surveys and studies it is hoped that our alleged to have made excessive discharges of oil and understanding of the deep-sea environment will reach a grease from 22 offshore rigs between May 1981 and Sep-

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