226 • Marine Minerals: Exploring Our New Ocean Frontier 



seasonally as environmental concerns warrant may 

 protect biota during sensitive stages of devel- 

 opment. 



Permanently changing the topography of the 

 seafloor may disrupt the spawning patterns of some 



marine species dependent on a particular substrate 

 type (e.g., salmon and herring). ^^ 



"S.J. de Groot, "The Potential Environmental Impact of Marine 

 Gravel Extraction in the North Sea," Ocean Management, No. 5 

 (1979), pp. 233-249. 



DIFFERENT EFFECTS IN SHALLOW AND DEEP WATER 



While the potential environmental impacts of 

 mining operations in shallow water are similar to 

 those in deep water, the effects may be more obvi- 

 ous in shallow areas and may have a more direct 

 effect on human activities. Many of the organisms 

 on the continental shelf and in coastal waters are 

 linked to humans through the food chain; decreased 

 animal productivity may have an adverse economic 

 effect as well as an undesirable environmental ef- 

 fect in these nearshore areas (see figure 6-2). 



Surface Effects 



Surface plumes are of more concern in nearshore 

 shallow water areas than they are in deeper areas. 

 In the open ocean, plankton productivity is lower 

 and populations extend over huge geographic 

 scales. The effects of a localized mining operation 

 on the surface biota, therefore, will be less in the 

 offshore situation. Visual and aesthetic effects from 

 mining operations and waste plumes also will be 

 less apparent far offshore. 



Water Column Effects 



High metal concentrations can reduce the rate 

 of primary production by phytoplankton and can 

 alter species composition and succession of 

 phytoplankton communities^** Several factors act 

 simultaneously to reduce the likelihood of adverse 

 effects from metals released during mining opera- 

 tions in shallow water. Water over the continental 

 shelf contains higher concentrations of particulate 

 matter (and organic chelating agents) which con- 

 vert the dissolved (ionic) metals into insoluble forms 

 that are unavailable to plankton^ ^ While no studies 

 have yet identified metal contamination of the water 

 column to be a serious consequence of seabed min- 



ing, the potential for metal persistence is greater 

 in the deep-sea. 



Benthic Effects 



Coastal waters are subject to continual wave ac- 

 tion and seasonal changes, and the species found 

 here are adapted to such conditions. The fine par- 

 ticulates stirred by mining operations may be sim- 

 ilar to sediment resuspended by strong wave action 

 in shallow water. In coastal areas, surface-living 

 forms have been found to tolerate 2 inches of sedi- 

 ment deposition, sediment-dwelling animals (infauna) 

 10 to 12 inches, and deeper burrowing bivalves 4 

 to 20 inches. ^^ On the other hand, animals accus- 

 tomed to the relatively quiescent deep ocean envi- 

 ronment may be less resilient to disruption of their 

 habitat or blanketing by particulates. Since deep- 

 sea animals live in an environment where natural 

 sedimentation rates are on the order of millimeters 

 per thousand years, they are assumed to have only 

 very limited burrowing abilities. Thus, even a thin 

 layer of sediment may kill these organisms. ^^ In 

 general, if the resident fauna on an area of the shal- 

 low seafloor are buried, the community will gen- 

 erally recover more quickly than in the deep-sea. 



Populations of animals direcdy within the min- 

 ing path will be destroyed. Dredged areas in shal- 

 low seafloor are buried, the community will recover 

 more quickly than in the deep-sea. 



^*Thomas and Siebert, "Effect of Copper." 

 "Huntsman and Sunda, "The Role of Trace Metals." 



''Consolidated Gold Fields Australia Ltd. and ARC Marine Ltd. , 

 Marine Aggregate Project, Environmental Impact Statement, vol. 1, 

 February 1980. 



^'P.A. Jumars and E.D. Gallagher, "Deep-Sea Community Struc- 

 ture: Three Plays on the Benthic Proscenium," The Environment 

 of the Deep Sea, Rubey Volume II, W.G. Ernst and J.G. Morin (eds.) 

 (Englewood'Cliffs, NJ: 1982); and P. A. Jumars, "Limits in Predict- 

 ing and Detecting Benthic Community Responses to Manganese Nod- 

 ule Mining," Marine Mining, vol 3. (1981), No. 1/2, pp. 213-229. 



