236 • Marine Minerals: Exploring Our New Ocean Frontier 



Figure 6-6.— Silt Curtain 



PIPELINE 





•*^5^ 



BOTTOM SEDIMENT 



SOURCE: Modified from U.S. Army Corps of Engineers, "Executive Overview and 

 Detailed Summary," Synthesis of Researoti Results, DMRP Program, 

 U.S. Army Corps Engineer Waterways Experiment Station, Vicksburg, 

 MS, Tectinical Report DS 78-22, December 1978. 



quent curtain movement would be necessary. "^^ 

 Once environmental effects are better defined, engi- 

 neering techniques can be developed to address 

 them. For example, Japanese industry has devel- 

 oped a system that may reduce turbidity in the 

 suface layers of the water column when sediment 

 is discarded. Air bubbles entrained in the water 

 during dredge filling and overflow exacerbate the 

 surface turbidity plume associated with hydraulic 

 hopper dredging. A system, called the "Anti- 

 Turbidity Overflow System" employed by the 

 Ishikawajima-Harima Heavy Industries Company, 

 Ltd., (IHI) reportedly separates air from the water 

 prior to overflow. According to IHI data, the re- 

 sult is a clear water column and, presumably, a 

 smaller area of fine sediment at the dredge site 

 caused by particles that settle rapidly. 



^'Barnard, Prediction and Control of Dredged Material Dispersion, 



p. 87. 



DEEP WATER MINING STUDIES 



In the deep-sea, the abundance of animal life de- 

 creases with increasing depth and distance from 

 land. Deep-sea animals are predominantly re- 

 stricted to the surface of the seafloor and the up- 

 per few inches of the bottom. Species, especially 

 smaller-sized organisms, are incompletely cata- 

 logued at present, and little information is avail- 

 able on their life cycles. The density of animals is 

 low but diversity may be high. In these regions, 

 the low total number of animals is thought to re- 

 flect the restricted food supply, which comes from 

 either residues raining into the deep sea from above 

 or from in situ production. ^° 



All estimates of the environmental impacts of 

 deepsea mining draw heavily on information from 

 the Deep Ocean Mining Environmental Study 

 (DOMES), the only systematic long-term research 

 program conducted in very deep water. Justifica- 

 tion for extrapolating from these deep-sea sites to 

 others rests on the hypothesis that, in general, the 

 abyssal ocean is a much more homogeneous envi- 

 ronment than shallow water environments. 



DOMES: Deep Ocean Mining 

 Environmental Study 



DOMES was a comprehensive 5-year (1975-80) 

 research program funded by NOAA. The goal was 

 to develop an environmental database to satisfy the 

 National Environmental Policy Act requirements 

 to assess the potential environmental impacts of 

 manganese nodule recovery operations.®* During 

 the first phase of DOMES, the environmental con- 

 ditions in the designated manganese nodule area 

 of the Pacific Ocean (i.e., the DOMES area) were 

 characterized to provide a background against 

 which mining-produced perturbations could be later 

 compared. These baseline studies were carried out 

 at three sites that covered the range of environ- 

 mental parameters expected to be encountered dur- 

 ing mining (see box 6-F). 



The mining scenario presumed removal of nod- 

 ules from the deep seabed by means of a collector 

 (up to 65 feet wide) pulled or driven along the 

 seabed at about 2 miles per hour. Animals on the 



™Deep-sea biomass often coirelates with piimaiy productivity above; 

 areas beneath low productivity subtropical waters may be an order 

 of magnitude lower in biomass per unit area than at high latitudes. 



•^'U.S. Department of Commerce, NOAA Office of Ocean Minerals 

 and Energy, Deep Seabed Mining, Final Programmatic Environmental 

 Impact Statehient, vol. 1, (Washington, D.C.: Department of 

 Commerce, September 1981). 



