Chapter 6 



Environmental Considerations 



INTRODUCTION 



Mineral deposits are found in many different 

 environments ranging from shallow water (sand, 

 gravel, phosphorites, and placers) to deep water (co- 

 balt crusts, polymetallic sulfides, and manganese 

 nodules). These environments include both the 

 most biologically productive areas of the coastal 

 ocean as well as the almost desert-like conditions 

 of the abyssal plains. (See figure 6-1.) 



Given this broad spectrum, it is hard to gener- 

 alize about the effects of offshore mining on the ma- 

 rine environment. However, a few generic princi- 

 ples can be stated.' As long as areas of importance 

 for fish spawning and nursery grounds are avoided, 

 surface and mid-water effects from either shallow 

 or deep water offshore mining should be minimal 

 and transient. Benthic effects (i.e., those at the 

 seafloor) will be the most pronounced for any min- 

 ing activity in either shallow or deep water. Ani- 

 mals within the path of the mining equipment will 

 be destroyed; those nearby may be smothered by 

 the "rain of sediment" returning to the seafloor. 

 Mining equipment can be designed to minimize 

 these effects. Barring very extensive mining sites 

 that may eliminate entire populations of benthic 

 organisms or cause extinctions of rare animals, neg- 

 ative impacts to the seafloor are reversible. Most 

 scientists believe that shallow water communities 

 would recover rapidly from disturbance but that 

 recolonization of deep sea areas would be very slow. 



Because little offshore mining is going on now, 

 the degree of environmental disturbance that any 

 particular commercial operation might create is dif- 

 ficult to characterize. Even areas that are dredged 

 frequendy do not have the same level of disturbance 

 as a continuous mining operation. Nevertheless, 

 U.S dredging experience is a useful gauge of the 

 potential for environmental impacts. In shallow 

 nearshore waters, a few sand, gravel, and shell min- 

 ing operations in the United States and Europe in- 



dicate possible impacts. In addition, results of re- 

 search in the United States and abroad offer insights 

 on the effects of offshore mining. These research 

 efforts include: 



• the International Council for Exploration of 

 the Sea (ICES) Report of the Working Group 

 on Effects on Fisheries of Marine Sand and 

 Gravel Extraction — box 6- A, 



• the U.S Army Corps of Engineers Dredge Ma- 

 terial Research Program (DMRP) — box 6-B, 



• the New England Offshore Mining Environ- 

 mental Study (NOMES)— box 6-C, 



• Sea Grant Studies of Sand and Gravel in New 

 York Harbor — box 6-D, and 



• National Oceanic and Atmospheric Admin- 

 istration's (NOAA) Deep Ocean Mining Envi- 

 ronmental Study (DOMES)— box 6-F. 



The Gorda Ridge Draft Environmental Impact 

 Statement, and the Cobalt Crust Draft Environ- 

 mental Impact Statement (see box 6-G) summarize 

 related research as well. 



Similarities among the mining systems used for 

 deep water (2,500-16,000 feet) and shallow water 

 (less than 300 feet) suggest that the same general 

 types of impacts will occur in both environments. 

 Any mining operation will alter the shape of the 

 seafloor during the excavation process, destroy 

 organisms directly in the path of operations, and 

 produce a sediment plume over the seafloor from 

 the operation of the equipment^. When the mined 

 material is sorted and separated at the ship, some 

 percentage will be discarded — very litde in the case 

 of sand and gravel, a great deal for many other 

 seabed minerals — resulting in a surface "plume" 

 that will slowly settle to the bottom (see figure 6- 

 2). The duration and severity of plume effects on 

 the surface and water column depend on the grain- 

 size of the rejected material. Sand (i.e., particle sizes 

 0.06 mm- 1.0 mm.) settles quickly; silts (.001 -.06 



'These conclusions are for mining alone. If any at-sea processing 

 occurs, with subsequent chemical dumping, guidelines may be totally 

 different. 



^'These sediment plumes are the equivalent of the dust clouds 

 produced by similar operations on land. 



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