Around 252 million tonnes of carbon is thought to be stored within Scotland’s iconic sea lochs, but new research warns that bottom trawling is posing a significant threat, with campaigners calling for Scottish ministers to do more to protect them.

Disturbing seabed sediments through trawling could cause significant losses of carbon stored in Scotland’s sea lochs, according to new research from the University of St Andrews.

The findings come as the Scottish Government prepares to launch a consultation on new fishing restrictions for marine protected areas and sensitive seabed habitats.

The study, published in Marine Environmental Research, found that organic carbon stored in seabed sediments can be released into the surrounding seawater when disturbed. Once released, the carbon is more likely to break down and return to the atmosphere as carbon dioxide, contributing to climate change.

Scotland’s sea lochs, which scientists classify as fjords, are important natural stores of so-called blue carbon – carbon captured and stored in marine and coastal ecosystems.

Despite being a fraction of the size of the North Sea, they are estimated to bury around 84,000 tonnes of organic carbon every year. Much of this carbon originates on land, carried into the lochs by rivers from surrounding peatlands before becoming trapped in seabed sediments.

Researchers found that even a single disturbance event caused rapid losses of sedimentary organic carbon, and that some areas were particularly vulnerable.

“Maximum disturbance effects will be felt at the upper end of the loch where the sediment is both high in organic-carbon content and in the most reactive forms of organic matter,” said lead author Lauren South, a PhD candidate in the School of Geography and Sustainable Development.

The researchers say existing maps of seabed organic carbon could be combined with data on fishing activity to identify where protective measures would have the greatest benefit.

“This is part of a growing body of research which points in the same direction: if we care about natural carbon stores it’s time to protect the most vulnerable seabed stores of carbon and those at the heads of these sea lochs in particular,” she added.

Charles Millar, executive director of the Sustainable Inshore Fisheries Trust, said the findings confirmed that the heads of Scottish sea lochs, which collect peat washed down from surrounding glens, contain some of the country’s most vulnerable carbon stores. “With Scottish peatlands at ever greater risk of fire, we must urgently act to protect our equally important seabed carbon from disturbance,” he said, calling for measures to protect these areas from trawling.

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