Ch. 6— Environmental Considerations • 239 



thic biota in about 1 percent of the DOMES area, 

 or 38,000 square nautical miles, may be killed due 

 to impacts from first generation mining activities. 

 Although recolonization is likely to occur after min- 

 ing, the time period required is not known. No ef- 

 fect on the water-column food chain is expected. 



The second important type of impact identified 

 is due to a benthic plume or "rain of fines" away 

 from the coUector which may affect seabed animals 

 outside the actual mining tract through smother- 

 ing and interference with feeding. Suspended sedi- 

 ment concentrations decrease rapidly, but the 

 plume can extend tens of kilometers from the col- 

 lector and last several weeks after mining stops. No 

 effect on the food chain in the water column is ex- 

 pected due to the rapid dilution of the plume. How- 

 ever, mining may interfere with the food supply 

 for the bottom-feeding animals and clog the respi- 

 ratory surfaces of filter feeders (such as clams and 

 mussels). Such effects will involve biota in an esti- 

 mated 0.5 percent or 19,000 square nautical miles 

 of the DOMES area. 



The third impact identified as significant is due 

 to the surface plume. Under the scenario, a 5,500- 

 ton-per-day mining ship will discharge about 2,200 

 tons of solids (mainly seafloor sediment) and 3 mil- 

 lion cubic feet of water per day. The resulting sur- 

 face discharge plume may extend about 40 to 60 

 miles with a width of 12-20 miles and will continue 

 to be detectable for three to four days following dis- 

 charge. As the mining operation is supposedly con- 

 tinuous (300 days per year), the plume will be vis- 

 ible virtually all the time. Surface plumes may 

 adversely affect the larvae of fish, such as tuna, 

 which spawn in the open ocean. The turbidity in 

 the water column will decrease light available for 

 photosynthesis but will not severely affect the 

 phytoplankton populations. The effect will be well 

 within the realm of normal light level fluctuations 

 and win resemble the light reduction on a cloudy 

 day. 



FoUow-Up to DOMES: 



Research by the National Marine Fisheries Serv- 

 ice, under NOAA's five-year plan, concluded that 

 the surface plume was not really a problem due to 

 rapid dilution and dissipation. This study identi- 

 fied another potential adverse effect that previously 



had not been considered — that of thermal shock to 

 plankton and fish larvae from discharge at the sur- 

 face of cold deep water. ^' However, except for mor- 

 tality of some tuna and billfish larvae (the two com- 

 mercially important fish) in the immediate vicinity 

 of the cold water (4-10° C) discharge, adverse ef- 

 fects appear to be minimal. 



Continued study of surface plumes suggests that 

 discharged particulates will not accumulate on the 

 pycnocline.®* Because new measurements show 

 much of the material discharged settled more slowly 

 than previously thought, the plumes will cover more 

 area. 



In June 1983, Expedition ECHO I collected 15 

 quantitative samples of the benthic fauna in the vi- 

 cinity of DOMES site C(15°N,125°W). These 

 samples were collected for a study of potential im- 

 pacts on the benthic community of a pilot-scale test 

 mining by Ocean Mining Associates, carried out 

 5 years earlier. Fauna from the immediate test min- 

 ing area were compared with fauna from an area 



''W.M. Matsumoto, Potential Impact of Deep Seabed Mining on 

 the Larvae of Tuna and BiUfishes, SWFC Honolulu Laboratory, Na- 

 tional Marine Fisheries Service/NOAA, prepared for NOAA Divi- 

 sion of Ocean Minerals and Energy, NOAA-TM-NMFS-SWFC-44, 

 Washington, D.C., 1984. 



"J.W. Lavelle and E. Ozturgut, "Dispersion of Deep-Sea Min- 

 ing Particulates and Their Effect on Light in Ocean Surface Layers," 

 Marine Mining, vol 3. (1982), No. 1/2, pp. 185-212. 



Pttoto credit: National Oceanic and Atmospheric Administration 



The box core sampler is a standard tool for studying 

 ocean bottoms. This particular sample, containing 

 manganese nodules, is from the DOMES area. Box 

 cores provide a relatively intact picture of the sediment 

 and animals in the top layers of the seafloor. 



