A pre-print study by European environmental scientists assesses the direct impact of the recent sabotage of the undersea Nord Stream pipelines on marine ecosystem. The explosions that ripped open the gas pipelines in the Baltic Sea last September released more than 100,000 tonnes of methane—which was widely covered in the media— and also stirred up some 250,000 tonnes of heavily contaminated sediment—which was not widely covered.

Baltic Sea natural gas release (Photo: Danish Defense)

As the researchers note in their paper, the four explosions that deliberately ruptured Nord Stream 1 and 2 took place near a major chemical munition dump site near the Danish island of Bornholm.

Explosion site map, with chemical munition dumpsite indicated, where 11,000 tons of chemical warfare agents were sea-dumped in 1947. Sanderson et al.

While the massive release of natural gas into atmosphere raised serious concerns for climate, this paper assesses the overlooked direct impact of this sabotage on marine ecosystem. Seals and porpoises within a radius of four km would be at high risk of being killed by the shockwave, while temporary impact on hearing would be expected up to 50 km away. As the Baltic Proper population of harbour porpoises (Phocoena phocoena) is critically endangered, the loss or serious injury of even a single individual is considered a significant impact on the population. The rupture resulted in the resuspension of 250,000 metric tons of heavily contaminated sediment from deep-sea sedimentary basin for over a week, resulting in unacceptable risks towards fish and other biota in 11 km³ water for more than a month.

—Sanderson et al.

In addition to the harbour porpoise—which is considered the most vulnerable in relation to the explosions, other marine mammal populations near the explosion sites are the Gray seal and the harbour seal.

The paper explores the environmental impacts of the pipeline explosions and release of gas by modeling potential impacts on marine ecosystem of the explosions themselves as well as toxic risk from resuspended contaminated sediments in the water.

Among the findings:

• The event released historically introduced pollutants to the deepest location of the Bornholm basin and resulted in large volumes of water exceeding the environmental toxic threshold for up to 34 days;these did not reach the surface of the sea nor the surrounding shores. The cause of marine environmental risk was primarily resuspension of TBT—an endocrine disrupter used to protect ship hulls—and Pb representing 75% of the total mixture toxicity contributions.

• The Bornholm Basin is the traditional spawning and nursery ground for the Eastern Baltic cod (Gadus morhua) population. The rupture happened at the end of the normal cod spawning season from March to September. The resuspension of toxic sediments could moreover reach fishes as well as juvenile cods and eggs in the area for more than a month. The most likely long-term impacts on fish would be endocrine disruption due to TBT exposure. Lead (Pb) exposure to fish may induce oxidative stress, affect biochemical and physiological functions among this disrupt neurotransmitters causing neurotoxicity and disruptions to the immune system. The contaminant load resulting from resuspension of sediments by this event likely adds more pressure on already existing ones, putting the e.g. the Baltic cod stock under additional stress.

Resources

• Hans Sanderson, Michał Czub, Sven Koschinski et al. (2023) “Environmental impact of sabotage of the Nord Stream pipelines,” PREPRINT (Version 1) available at Research Square doi: 0.21203/rs.3.rs-2564820/v1