Impeded Macrofaunal Colonization and Recovery Following Marine Deposition of Inert and Organically Modified Mine-Tailings

• Published in: Frontiers in Marine Science Vol. 7
• Main Authors: Sweetman, Andrew K., Haugland, Barbro T., Kvassnes, Astri J. S., Bolam, Stefan G.
• Format: Journal Article
• Language: English
• Published: Lausanne Frontiers Research Foundation 19.08.2020; Frontiers Media S.A
• Subjects: Abundance; Benthic environment; Benthos; Biodiversity; Biomass; Coastal zone; Colonization; Community composition; Community structure; Deposition; ecosystem recovery; Estuaries; Experiments; macrofauna; marine benthos; Marine environment; Metals; Mine tailings; Mine wastes; Mineral resources; Minerals; Ocean floor; Ores; organic carbon; Organic matter; Recovery; Sediments; Species richness; United Kingdom > UK; England; Norway
• ISSN: 2296-7745; 2296-7745
• DOI: 10.3389/fmars.2020.00649

Fine-grained, waste rock (or tailings) produced during mining processes are the main waste product following the extraction of valuable minerals and metals from ores. The proximity of mineral resources to coastal regions in some countries has meant that the organically inert mine tailings are often deposited into the marine environment as a submarine tailings placement or STP. This creates a real environmental challenge since the deposition of tailings at the seafloor can completely smother the benthic environment and reduce benthic biodiversity and alter ecosystem function. A limited number of studies have attempted to quantify the speed of seafloor recovery following tailings disposal and have suggested that one of the main factors limiting seafloor colonisation is the lack of organic matter of the tailings deposited. In this experimental study, we used hydrodynamically unbiased settlement trays within a complete randomised block design to test whether macrofaunal colonisation of mine tailings, and resemblance towards ambient assemblages, is enhanced when tailings become more enriched in organic C (Corg). Our experiment showed that tailings with Corg contents 1% exhibited lower faunal abundance and biomass and different macrofaunal community composition after one year compared to background sediments. Macrofaunal species richness (defined as the total number of different taxa) in the 0% and 0.5% Corg tailings treatments, however, was statistically indistinguishable from ambient intertidal sediments after one year. Furthermore, macrofaunal community structure was more similar to that of the background intertidal sediments after one year, which collectively suggest partial recovery of seafloor biodiversity in tailings with zero to low Corg levels. Nevertheless, macrofaunal abundance and biomass in these treatments remained significantly less than the background community after one year suggesting factors other than the Corg content of tailings may be structuring macrofaunal colonisation and impeding seafloor recovery of tailings deposits. We propose that the non-marine physical structure of the tailings particles, which show great angularity is predominantly responsible for the observed delayed recovery.