Dredging and trawling carbon cost: New study quantifies seabed disturbance

A new study from the University of Exeter and Bangor University has produced the first long-term estimates of how port dredging and marine aggregate extraction disturb organic carbon stored in seabed sediments. The research found that port dredging across the Northwest European shelf disturbed an average of 2.2 million tonnes of organic carbon per year between 1995 and 2021. Marine aggregate extraction added another 0.4 million tonnes per year. The study combined Victorian-era archives with modern seabed data to track changes since the 1800s. While the carbon impact of dredging and aggregate extraction is significant, the study notes it is roughly three orders of magnitude lower than bottom trawling, which disturbs far larger areas of carbon-rich muddy seabeds. Ports and harbours are often located in muddy estuarine environments with higher carbon concentrations, making them a priority for protection. The researchers say the findings offer policymakers a clearer basis for targeting the highest-impact activities and protecting carbon-rich seabeds.