Norwegian mine tailings experiment
The first set of experiments to determine the impact of mine waste (tailings) on seafloor life are underway at the International Research Institute in Stavanger, Norway. Deep-sea mining activities will indisputably affect the status of the marine environment. In addition to the direct disturbance of the seafloor substrate, mining operations will create extensive sediment plumes. Resettlement of particles from these plumes away from the mining site will smother the sediment and benthic fauna with unforeseen consequences. The impacted area may therefore be a multifold of the area that is actually mined and novel scientific data are critically needed to establish how significant the impacts of mine tailing deposition actually are.
Above: views from the RV MS Solvik during the sampling exercise
These exposure experiments - a collaborative effort between MIDAS teams at IRIS, NIOZ and University of Gent - are designed to determine the effects that the settling of resuspended particles might have on the seafloor fauna. We investigated the response of soft-sediment biota to the deposition of ground-up rock (mine tailings) on deep-sea sediments collected from a Norwegian fjord. Sediment was supplied from cores collected in late October aboard RV MS Solvik from a site at 200 m water depth in the Hardangerfjord in south west Norway. After a short, early morning steam through the beautiful fjords (see movie below), we reached the site named ‘MIDAS 2014’ where we collected 42 sediment cores for our laboratory experiments.
As a consequence of deposition of mine tailings, a large part of the seafloor benthos will be buried, cutting them off from the supply of organic matter and oxygen and causing mortality or reduced biotic activity. We examined the impact of tailing deposits of three thicknesses (1, 5 and 30 mm; see image above) compared to a control without tailing deposits. As response variables, we chose to determine i) the oxygen conditions in the sediment; ii) the structure of the main components of seafloor biota, namely bacteria, meiofauna and macrofauna; iii) the total sediment community oxygen consumption (SCOC) as a measure of total activity, and iv) the capacity of the seafloor community to process organic matter (13C-labelled diatoms). These response variables will allow us to establish the impact of aberrant tailing deposits on the structure and consequently the functioning of seafloor communities. The images below show some of the core processing at the end of the incubations. Analyses are currently underway and some initial findings are expected to be available to share at the ASLO meeting in February 2015.
Above, from left:. Tanja Stratmann (NIOZ), doing the sediment microprofiling under in situ bottom water temperature of 8°C, in the absence of light, using Unisense micro-electrodes; Annelien Rigaux (UGent, Belgium) processing cores; Lisa Mevenkamp (UGent) processing meiofauna samples. In order to better differentiate the dead from living nematodes, Lisa used the time consuming method of Trypan Blue. In contrast to conventional stains e.g. Bengal Rose that stains living and dead cytoplasm or tissue, Trypan blue only attaches to dead specimens. This is of crucial importance as treatment related mortality may be masked if dead specimens have not degraded within the experiment period.
Above: Movie clip showing finely crushed rock (mine tailings) being added to the top of a sediment core in order to monitor the effects of sediment burial on the organisms.