THE ECOLOGICAL IMPACTS OF SUBMARINE TAILINGS PLACEMENT

Most of the 2500 industrial-size mines operating around the world dispose of their tailings on land. For technical, spatial, and chemical reasons this is not always feasible, and attention has shifted to submarine tailings placement (STP) and deep-sea tailings placement (DSTP). Marine disposal presents numerous challenges that can have significant environmental impacts across a range of ecosystems. This review describes the processes at the basis of the disposal rationale and how these can affect its outcome, and outlines the ecological impacts that are associated with or interact with these processes. Mine waste disposal on to the seafloor appears to be poorly understood given the extent of its implementation. The uncertainty surrounding this method extends to our understanding of both biophysical processes and ecological impacts. For example, the potential role of vertically migrating species in transporting mine-disposed trace elements from deeper environments into the shallower surface layers has been largely overlooked, and, similarly, the nature, extent, and impact of secondary plumes that develop off the main tailings current are poorly described and quantified, as is their interaction with migrating biota. Furthermore, the vulnerability of deep-sea environments to human impacts and their potential for recovery remains largely unknown. Given the large degree of uncertainty around the impacts of this practice on a wide range of ecological communities, coupled with the high connectivity of both deep-water and pelagic environments, it is imperative that participating countries, the global scientific community, and managing entities act urgently to bridge these knowledge gaps, improve management practices, and take a more precautionary approach to the implementation of STP and DSTP.