THE IMPACT OF commercial-scale mining for polymetallic nodules on deep-sea ecosystems remains a big question amongst scientists.
Historically, the first commercial deep-sea test mining was carried out almost 50 years ago, and only a few small-scale commercial test mining or scientific disturbance studies have been carried out since.
Those studies imply immediate severe impacts after mining, but fewer impacts over the longer term.
A paper called ‘Biological responses to disturbance from simulated deep-sea polymetallic nodule (1) mining’ by a number of authors and published in Journals.plos.org, February 8, 2017 (2) mentions seven sites in the Pacific where multiple surveys assessed recovery in fauna over periods of up to 26 years.
“Almost all studies show some recovery in faunal density and diversity for meiofauna and mobile megafauna, often within one year.
“However, very few faunal groups return to baseline or control conditions after two decades. The effects of polymetallic nodule mining are likely to be long term.
“Our analyses show considerable negative biological effects of seafloor nodule mining, even at the small scale of test mining experiments, although there is variation in sensitivity amongst organisms of different sizes and functional groups, which have important implications for ecosystem responses.
“Unfortunately, many past studies have limitations that reduce their effectiveness in determining responses. We provide recommendations to improve future mining impact test studies.
“Further research to assess the effects of test-mining activities will inform ways to improve mining practices and guide effective environmental management of mining activities.”
Uncertainty around the effects of sediment plumes has been at the centre of seabed mining consents in this country and the future of deep-sea trawl fishing.
Last month our National Institute of Water and Atmospheric Research (NIWA) launched a very challenging scientific underwater experiment 500 metres deep on the Chatham Rise to measure longer term effects and potential recovery of seabed communities.
The project, which will be repeated for two years, is a collaboration among NIWA, Waikato and Victoria Universities, with additional input from Okeanus Science and Technology (USA) and Delft Technical University (Netherlands). The research is funded by the MBIE.
In the first survey, around nine separate highly specialised pieces of equipment were deployed from NIWA‘s research vessel Tangaroa, that included three undersea observational platforms known as benthic landers, a multi-corer to take sediment samples, seabed moorings, water column sampling equipment, an underwater camera that will be towed above the seafloor and a “benthic disturber” to create a sediment plume.
The benthic landers, which have been built by NIWA and not yet used at sea, carry a variety of high definition cameras, lights and instruments to record physical, chemical and biological activity.
The dispersal of the plume was then monitored, and surveys done before and after the disturbance to measure the effects on seabed animals.
Voyage leader and NIWA principal scientist Dr Malcolm Clark admits that deploying so many instruments on the one experiment is “extraordinarily complex”.
The data collected will be used to build up a picture of how the biological communities on the seabed may be affected by the sediment stirred up by mining or bottom trawl fishing.
“These activities create plumes of sediment, but we don’t know how the sediment affects seabed life as it settles again on the seafloor, and how much deep-sea animals can withstand,” says Clark.
“We are doing this experiment on a small scale on the Chatham Rise, but it will give us a much better idea of how environmental managers and industry can work to mitigate larger-scale disturbance effects.”
Three seabed moorings are also being installed at an undisturbed control site where they will remain for a year. The information they record will be used for comparison with the disturbed area.
A laboratory programme will run alongside the work at sea that will provide further information on the resilience of the seabed ecosystem. The research team will collect live sponges and corals and bring them back to a NIWA laboratory where their resilience to various sediment loads will be tested.
“We will compare the measurements taken during the Chatham Rise disturbance experiment with a controlled experiment in the lab, which may be able to tell us the tipping point at which these communities either cope well or are significantly impacted. The field and laboratory studies together will be a powerful combination to address when too much sediment is ecologically significant,” Clark says.
The survey was the first of three with monitoring to be repeated in 2019 and 2020.
(1) Polymetallic nodules are potato-sized concretions enriched in nickel, copper and cobalt. These nodules also contain metals and non-metals important to green-tech enterprises, such as electric vehicles and wind energy production.