Environmental impact assessment studies for deep sea manganese nodule mining have been initiated in the Central Indian Ocean Basin since 1995. As a part of the first phase for collecting the benthic baseline data, echo sounding, sub-bottom profiling, seabed photography, coring and sampling have been carried out at close intervals in 5 selected areas (of 10x10 miles each). Detailed studies on topographic undulations, nodule distributions and sediment characteristics have resulted in the selection of Test and Reference Areas. A strip of 3000 200 m was disturbed with a hydraulic device, so as to cause suspension and redistribution of sediment in the near bottom waters and the impact on the seabed as well as dose to the bottom was observed. Results show that most of the disturbance is restricted to the disturbed area with some resedimentation in adjacent areas, whereas no significant mention of sediment in the bottom waters is observed. A longterm monitoring of the environmental Impact of the Benthic Disturbance has been planned in the study areas.
Environmental impact assessment has become an important part of deep-sea mining projects especially due to awareness and need for conservation of ecological status of the marine environment. The deep-sea mining has an advantage of being an activity of the future wherein our previous experiences of environmental impacts of land-based mining projects can be applied for maintaining the ecological balance. With this in view, some of the research groups, from the countries involved in the deep-sea mining ventures, have initiated multi-disciplinary environmental studies in the Pacific Ocean, such as the DISCOL (Germany), BIE (USA), JET (Japan) and IOM BIE (Interoceanmetal). All of these have focussed on selecting a test site and monitoring the pre- and post-disturbance environmental conditions for assessment of the environmental impact (FOELL, 1990; TRUEBLOOD, 1993; MMAJ, 1994).