240 • Marine Minerals: Exploring Our New Ocean Frontier 



far enough away to have been undisturbed. Dis- 

 turbance to the seafloor was either not extensive 

 enough to produce a statistically detectable differ- 

 ence in community structure from unaltered areas, 

 or recovery had taken place within 5 years. ^^ Con- 

 clusions were that the test mining was not indica- 

 tive of an actual mining operation. Future research 

 will include some short-term (30-day) sedimenta- 

 tion studies to try to characterize the response time 

 of benthic animals to plume effects. ^^ 



Recommendations for future research include: 



• studying a much larger mining effort or other 

 similar impact on the benthos, 



• sampling at the same sites previously sampled 

 to develop trends over time, and 



• evaluating data to detect differences at a com- 

 munity level, not at individual or species 

 levels. 



Environmental Effects From 

 Mining Cobalt Crusts 



The environmental baseline data that DOMES 

 collected and the conclusions it drew about poten- 

 tial impacts of nodule mining are somewhat appli- 

 cable to mining cobalt crusts. The environmental 

 setting described from the DOMES area has much 

 in common with proposed crust sites. DOMES sta- 

 tions span the central and north Pacific basins and 

 are in areas meteorologically similar to the Hawai- 

 ian and Johnston Island EEZs. The environment 

 studied was typical of the tropical and subtropical 

 Pacific in terms of water masses, major currents, 

 and vertical thermal structure. Species recorded in 

 the water column of the DOMES area are all char- 

 acterized as having broad oceanic distributions. The 

 settings differ primarily with respect to topography 

 and bottom type. The crusts occur on the slopes 

 of seamounts with little loose sediment, while the 

 nodule mine sites occur on plains carpeted with 

 thick sediments. The two areas consequently dif- 

 fer in their potential for resuspension of sediments. 



Baseline benthic biological data collected in the 

 DOMES study area are less analogous to the crust 

 sites than are the water column pelagic data. The 



chief depth range of interest for crust mining is 

 2,500 to 8,000 feet. Bottom stations sampled in the 

 DOMES area varied in depth from 14,000 to 

 17,000 feet. Communities would be different be- 

 cause of the substrate as well as the depth. The 

 DOMES sites consist of soft sediments interspersed 

 with hard manganese nodules; the crusts are hard 

 rock surfaces with little sediment cover. The com- 

 munities actually living on the manganese nodule 

 hard surfaces may resemble the fauna on the crust 

 pavement because the substrate composition is very 

 similar. 



Plume Effects 



As part of the Manganese Crust EIS Project, 

 mathematical models were constructed to simulate 

 the behavior of surface and benthic discharges.^' 

 This effort was based upon extensive modeling of 

 dredged material discharge dispersion conducted 

 for the Army Corps of Engineers' Dredged Mate- 

 rial Research Program. ^^ ^^ 



Surface Plume. — The DOMES data indicate 

 that a mining plume will increase suspended par- 

 ticulate matter in the water by a factor often. This 

 would effectively halt photosynthesis about 65 feet 

 closer to the surface of the water than normal. 



The results of field measurements made during 

 the DOMES program were extrapolated to com- 

 mercial-scale discharges and it was estimated that 

 the surface plume could reduce daily primary pro- 

 duction by 50 percent in an area 1 1 miles by 1 mile 

 and by 10 percent over an area as large as 34 miles 

 by 3 miles. The shading effect will only persist un- 

 til the bulk of the mining particulates settle, usu- 

 ally within a period of less than a day. Since it takes 

 phytoplankton 2 to 3 days to adapt to a new light 

 regime, the short-term shading effect of particu- 

 lates is not likely to affect the light-adaptation char- 



'^Spiess et al., Environmental Effects of Deep Sea Dredging. 

 ""Ed Myers, NOAA, pers. comm., OTA Workshop on Evironmen- 

 tal Concerns, October 1986. 



"E.K. Noda & Associates and R.C.Y. Koh, "Fates and Trans- 

 port Modeling of Discharges from Ocean Manganese Crust Mining," 

 prepared for the Manganese Crust EIS Project, Research Corpora- 

 tion the University of Hawaii, Honolulu, HI, 1985. 



"B.H.Johnson, 1974, "Investigation of Mathematical Models for 

 the Physical Fate Prediction of Dredged Material," U.S. Army Engi- 

 neer Waterways Experiment Station, Vicksburg, MS, Hydraulics Lab- 

 oratory, Technical Report D-74-1, March 1974. 



"M.G. Brandsma and DJ. Divoky, 1976, "Development of Models 

 for Prediction of Short-term Fate of Dredged Material Discharged in 

 the Estuarine Environment," Tetra Tech, Inc., Pasadena, CA, Con- 

 tract Report D-76-5, May 1976. 



