During the Indian Deep-sea Environment Experiment (INDEX), >6000 cu.m. of sediment was resuspended 5 m above seafloor. Data collected from deep-towed photography, sediment traps, sediment coring and CTD operations before and after the experiment in 1997, as well as photography and coring during 2001 and 2002 (only coring) were used out to evaluate the immediate effects of benthic disturbance and subsequent restoration of benthic environment. Results from sedimentological, geotechnical, geochemical, biochemical, microbiological and benthos analyses indicate a complex process of partial restoration of conditions and selective recolonisation of the benthic environment.
Arising from the need for prediction of potential impact of mining on marine ecosystem, the project on ‘EIA studies for nodule mining in CIB’ was initiated by collecting baseline data in the area in 1996. Benthic impact experiments for deep-sea mining have been conducted in the Pacific Ocean using plow harrow (Foell et al., 1990), as well as sediment resuspension device called ‘Deep-Sea Sediment Resuspension System’ DSSRS (Trueblood 1993, Fukushima 1995, Tkatchenko et al. 1996). DSSRS was also used for the Indian Deep-sea Environment Experiment (INDEX) in CIB during 1997 for conducting studies on impact of sediment suspension and resettlement (Sharma and Nath 1997, Sharma et al. 2000). Currently, longterm monitoring of restoration and recolonisation of benthic environment is underway. First cruise for monitoring the restoration of benthic environment was conducted during March-April 2001 followed by second monitoring cruise during May-June 2002 and third cruise during March-April 2003 onboard RV AA Sidorenko. During these cruises, data were collected in and around the disturbance zone in the test area at locations where pre- and post-disturbance data were also collected during the benthic disturbance experiment in 1997, in order to evaluate the extent of restoration of environment in the area.
