Trawling and mining could unleash carbon dioxide from the seabed

Disturbed seabeds could be a potent source of carbon dioxide pollution, according to a new study.

The research, published in Estuarine, Coastal and Shelf Science, raises questions about the impact of fishing trawling, deep-sea mining, and other ocean activities.

“Researchers have long assumed that physical disturbances of the seabed, such as from fishing equipment like trawling, increase the conversion of organic carbon into carbon dioxide, but theoretical models have lacked documentation in the form of measured values,” says lead researcher Dr Christian Lønborg, from the Institute for Ecoscience at Aarhus University, Denmark.

“We have now shown through laboratory experiments that this is indeed the case.”

The researchers collected sediment cores and seawater from the Danish coast and set them up in different chambers in a laboratory.

Over 18 weeks, the team regularly agitated some chambers, disturbing the sediment inside, while others were left still.

They measured the concentrations of nutrients and organic carbon in the soil of each sample, as well as the CO₂ dissolved in the seawater.

Disturbed samples released significantly more carbon dioxide into the water, and had lower organic carbon and nitrogen content in their soils.

These samples also consumed more oxygen from the seawater, in order to turn the carbon into CO₂, leading to oxygen-depleted water that can also affect marine life.

“If we are to assess the impact of trawling equipment, dredging and extraction of raw materials from the seabed, these consequences must also be considered,” says Lønborg.