For the ecological risk assessment of mining of Seafloor Massive Sulfides (SMS), three kinds of ecological risk that could be caused by the mining were identified using a mining plan. To assess the effect of the direct disturbance of seafloor on benthic organisms, the ecosystem model that deals with recovery process of benthos from elimination with the direct disturbance was developed. This model is available for the assessment of sedimentation of particles suspended by mining and discharging of waste water from mining support vessels. The ecosystem model that can deal with a kind of typical organisms in chemosynthetic ecosystems is to be employed for the assessment of a change in DO in benthic layers by discharging of waste water. In addition, diffusion models of suspended particles in ocean were developed. Combining the ecosystem model with the diffusion models, the ecological response on certain areas far from the mining or discharging points could be assessed. These efforts are expected to be contributed to the ecological risk assessment of SMS mining.
On and under deep seafloor of oceans in the world, there are mineral and energy resources such as Seafloor Massive Sulfides (SMS) and Methane Hydrate. SMS are formed by deposition of metal sulfides precipitated from hydrothermal fluids venting from seafloor. Methane Hydrate is an icy crystalline solid consisting of methane and water to be stable at high-pressure and low-temperature conditions corresponding to shallow geological formations beneath the seafloor deeper than several hundred meters depth. Recent rising of price of metal and fossil fuel resources due to the economic development of emerging countries has promoted the proposition of development of these resources. There are many hydrothermal vent fields in offshore of island countries in the western Pacific such as Papua New Guinea, New Zealand and Japan.
