Environmental Considerations of Nodule Mining in Central Indian Basin

Abstract

ABSTRACT The status of benthic population and their physical and chemical environment in the CIB have been evaluated. The information on nodule populations and their association with benthic activity leads to prediction of potential mortality of benthic fauna as well as the area of seafloor and the volume of sediment expected to be disturbed due to nodule mining. The resulting environmental implications due to large scale mining are expected to be in the form of 'plume' at the seafloor, turbidity in the water column and addition of bottom waters to the surface resulting in change in productivity patterns. Hence, the design of mining system should ensure that the sediments are seived off at the seafloor, strip mining be carried out to allow repopulation by nearby organisms and that there is no effluent discharge in the water column or at the surface to avoid change in ecology due to transportation by currents. However, the location of the CIB is such that the impact of mining on environment is likely to be minimal. INTRODUCTION India has embarked on the second stage of its endeavour towards exploitation of nodule deposits in the CIB. After having evaluated the potential resource available and having acquired exclusive rights under the UN law of the sea, it is conducting seafloor surveys for identification of mine-site and areas for relinquishing. At this stage, a review of various environmental characteristics of this area is essential, so as to use this information in the design of the proposed mining system as well as to predict the potential impact. The mining activity is expected to cause large scale disturbance not only at the seabed from where nodules will be lifted, but also in the water column as well as at sea surface resulting in widespread changes in the marine ecosystem. The potential impact of mining, based on model studies and pilot mining tests, is known to be varied and to some extent unpredictable1 - 11 and needs a cautious approach towards the problem of environmental conservation. This paper evaluates the existing environmental status of the CIB as well as the association of nodules with seafloor features. Based on this information, an attempt is made to predict potential disturbance in terms of seafloor area as well as volume of sediment and mortality of benthic organisms due to large scale mining activity in the area. Certain design parameters to minimise the deletrious effects of mining have also been dicussed. DISTRIBUTION OF NODULES AND ASSOCIATED FEATURES The seabed comprises of bottom sediments, diverse sedimentary structures mainly of biogenic origin, polymetallic nodules, massive rocky exposures and mineral encrustations, as well as the abyssal benthos. Of the three main varieties of sediment found in the Central Indian Basin, siliceous ooze predominates the area. There is a thin strip of calcareous foraminiferal and coccolithous ooze in the west, while in the south there are red clays12.