Environmental impact researches for manganese nodule mining have been progressive in many countries. The current status in the world is introduced. Fundamental understanding about deep-sea environment obtained by the Japan's research and results of the impact experiment to it are introduced. Requirements of in, situ long term and continuous monitoring, and engineering problems for the commercial scale mining are discussed. Future subjects for further progresses in the research are also mentioned.
Deep-sea manganese nodules, which have been found in large quantities at the Clarion-Clipperton Zones (CCZ)in the Pacific, have been focused as potential resources for Cu, Ni, Co, and Mn in the next generation. Three major sources of in-situ environmental impacts are expected during manganese nodule mining. They are collector tracking on seafloor, a seafloor plume by discharged sediments from a collector, and a surface plume from a mining ship as shown in Fig. 1. During manganese nodule mining, a large amount of deep-sea sediments is recovered from seafloor with nodules by a collector. Most of the recovered sediments are separated from the nodules and discharged from the collector immediately. They make sedimentwater mixture, suspend near the seafloor as a sediment plume, and settle on the seafloor again finally. Severe damage of seafloor benthos may occur with this resedimentation, because the sedimentation rate is very high compared with the one under the natural condition. Environmental impact research for manganese nodule mining was initiated in 1989 in Japan (Kajitani, 1997) following the USA's and German projects. The objective is to establish an effective method of environmental assessment and to develop some guidelines for prevention of mining impacts. Following five years of planning and baseline studies of the environment in the Japanese mining claim, the Japan Deep'sea Impact Experiment (JET) was conducted in 1994.
