Assessment of environmental effects of deep ocean mining of manganese nodules

Abstract

Deep ocean mining for manganese nodules is under development by several multinational mining consortia. Initial estimates of probable environmental effects of this mining were made before any actual operations were conducted. Recent pilot mining tests near Hawaii have provided an opportunity to verify and modify the initial estimates. The two principal initial impacts of mining are in the near surface water associated with increased turbidity caused by mining discharge, and in a relatively limited zone at the sea floor associated with collector traverse. Examples are presented of estimates of reduction in primary production in the turbid plume as well as the contrasting effect of increased nutrients. Effects of the mining collector on benthic populations are considered. The limitations of extrapolation of results obtained during pilot mining tests are discussed.