Benthic disturbance and impact experiments in the Central Indian Ocean Basin

As a part of the Environmental Impact Assessment studies for nodule mining, a long-term program has been initiated in the Central Indian Basin. Multid isciplinary studies on geological, biological, physical, and chemical param eters were carried out in an area selected on the basis of baseline data co llected in the first phase of the program. A benthic disturbance was simula ted with a hydraulic device also used in the previous experiments irt the P acific Ocean. A site of 3, 000 x 200 m was repeatedly disturbed by a combin ation of fluidizing pump and suction pump to dislodge and discharge sedimen t from the seafloor into the water column 5 m above the seafloor During 9 d ays of operation, 26 rows were carried out for 47 h of disturbance, resuspe nding about 6,000 m(3) of sediment along an 88-km line. Data for postdistur bance impact assessment were collected with sediment traps, deep-towed came ras, seafloor samples, and conductivity-temperature depth sensor (CTD)-rose tte observations. Seafloor data, sediment samples, and water column studies were aimed at evaluating the impact of benthic disturbance, on the basis o f pre- and postdisturbance data collected during the experiment. Observatio ns show that vertical mixing of sediment as well as its lateral movement an d resedimentation because of plume migration alters various parameters and leads to changes in the environment around the area.