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Topic: Mining waste

Dyngadjupet i Jøssingfjorden

Researchers at the IMR receive sediment samples from the former marine disposal site at Dyngadjupet in Jøssingfjorden in Rogaland.

Photo: Erlend A. Lorentzen/IMR

Dumping mining waste in the sea or fjords can have a negative impact on marine ecosystems.

Our coast and fjords provide a number of ecosystem services; for example, they are important production areas for many of our commercially important fish stocks.

The coarser-grained particles in mining waste fall to the seabed quite quickly. However, fine-grained particles can be carried by currents and affect a much wider area. This means that they can also affect life further away and higher up the water column.

Negative impacts on fauna and the environment

Dumping large quantities of sand and other material will have a big impact on fauna living at the bottom of the sea, and it may even completely wipe out existing ecosystems at the marine disposal site itself. In addition, the surroundings of the disposal site will be affected by the smallest rock particles in the tailings, with the area affected depending on the currents and quantity of waste.

The affected areas of the seabed, often covering several square kilometres, may become unproductive for as long as waste is dumped, and probably for many decades thereafter.

Demersal fish, bristle worms and crustaceans will lose their habitats. The latter two are eaten by many fish, which will thus have less access to food. Even just a few millimetres of tailings can change the composition and quantity of small animals in sediments. Particles from mining waste will affect the physiology of benthic organisms such as sponges and other filter feeders

Over the longer term, exposure to mining waste may reduce the density of sponges, in turn causing important ecosystem services to be lost.

Fjords that are potential disposal sites for mining waste may be spawning grounds and habitats for various species of fish, but no research has documented the direct or indirect impacts of mining activities and mining waste on fish.

Mining activities such as blasting create pressure waves that can propagate into the water if the mine is close to the fjord. This may scare fish away, causing spawning to be interrupted or to move to an area that is less favourable to the survival of their eggs, larvae and juveniles. Fish are especially vulnerable during their early life stages, so this may reduce or prevent recruitment to the population. This may have a particularly big impact on local fish populations that are genetically distinct. The fine fraction of the tailings has been shown to adhere to fish eggs, reducing buoyancy and affecting hatching time and larval survival.

Copepods like the Calanus finmarchicus will eat the small particles in the tailings. Copepods, in turn, are an essential food source for both fish and fish larvae, so any reduction in their nutritional value and survival rate may cause indirect impacts higher up the food web.

The advice of the Institute of Marine Research

The Institute of Marine Research (IMR) advises against establishing disposal sites:

  • near important spawning grounds for fish, or if the fjord’s ability to produce juvenile fish would be negatively affected
  • in or by national salmon fjords or in marine protected areas
  • if the mining waste contains potentially toxic chemicals that have not been environmentally tested, or that have not been documented as safe for seafood
  • if the mining waste contains excessive levels of heavy metals
  • if the dispersion of the fine fraction would be extensive or have a negative impact on the upper water layers, or if there is great uncertainty about the dispersion of the fine fraction

On account of the great variety in the measures for which waste permits are requested, and because environmental conditions differ between fjords, the IMR recommends that thorough environmental surveys be performed on a case-by-case basis. The surveys should make use of impact assessments based on good models.