Estimating historic seabed carbon disturbance by port dredging and aggregate extraction in NW Europe

RESEARCH ARTICLE Estimating historic seabed carbon disturbance by port dredging and aggregate extraction in NW Europe Ellie Maynard 1*, Zoë A. Roseby2, James D. Scourse2, Sophie L. Ward3, Callum Roberts1, Ruth H. Thurstan 1, Ciarán McLaverty 1 1 Centre for Ecology and Conservation, University of Exeter, Cornwall, United Kingdom, 2 Department of Earth and Environmental Sciences, University of Exeter, Cornwall, United Kingdom, 3 School of Ocean Sciences, Bangor University, Wales, United Kingdom * Abstract OPEN ACCESS Citation: Maynard E, Roseby ZA, Scourse JD, Ward SL, Roberts C, Thurstan RH, et al. (2026) Estimating historic seabed carbon disturbance by port dredging and aggregate extraction in NW Europe. PLoS One 21(5): e0349191. https://doi.org/10.1371/journal.pone.0349191 Editor: Lee W Cooper, University of Maryland Center for Environmental Science, UNITED STATES OF AMERICA Received: December 8, 2025 Accepted: April 26, 2026 Published: May 27, 2026 Copyright: © 2026 Maynard et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data availability statement: All relevant data used in this study are from publicly available datasets described within the manuscript and its Supporting Information files. The extent to which different human activities disturb seabed carbon, the largest long-term organic carbon reservoir on the planet, is poorly understood. Research to date has focused primarily on bottom trawl fisheries, but industries that target and extract marine sediments are likely to disturb significant masses of sedimentary organic carbon. This can lead to its remineralisation and reduce the capacity of the ocean to absorb atmospheric CO2. In this study, we combine archival documents, industry records, and published seabed substrate data, to estimate historical disturbance of sedimentary organic carbon on the Northwest European Shelf (NWES) from port dredging activities and marine aggregate extraction. Monte Carlo simulations were used to provide probabilistic estimates of annual carbon disturbance and associated upper and lower bounds (5th and 95th percentiles, respectively). Based on annual Monte Carlo simulations run between 1995−2021, our results suggest that port dredging over the shelf area disturbed 2.2 ± 0.9 Mt organic carbon year-1. In the case of marine aggregate extraction, simulations run between 1955−2022, suggest that marine aggregate extraction disturbed 0.4 ± 0.3 Mt organic carbon year-1. At a country scale, analysis of activities in UK waters suggest that organic carbon disturbance from port dredging and aggregate extraction activities are approximately three orders of magnitude lower than published estimates of disturbance by bottom trawling. Nevertheless, historical and contemporary port dredging and aggregate extraction present substantial and spatially concentrated sources of anthropogenic carbon disturbance that have not been systematically quantified across the Northwest European Shelf until now. These findings therefore address an important knowledge gap and have the potential to inform marine management and conservation strategies aimed at minimising organic carbon loss from the seabed. Funding: This study was funded by Convex Seascape Survey, with E.M., C.M., C.R., Z.A.R., PLOS One | https://doi.org/10.1371/journal.pone.0349191 May 27, 2026 1 / 20 J.D.S., S.L.W., and R.H.T. supported by funding from this project. Competing interests: The authors have declared that no competing interests exist. Introduction Continental shelf sea sediments are a primary sink of organic carbon in the ocean [1]. Organic carbon accumulates in marine sediments, sourced from either terrestrial environments or marine environments [2,3]. Despite forming around 7% of the global ocean by area [4], sediments on continental shelves contribute up to 40% of inorganic and 80% of oceanic organic carbon accumulation [5]. Shelf sediments therefore play a critical role in carbon accumulation and sequestration [6], absorbing ~0.2 petagrams (Pg) of carbon annually across the globe [7]. When seabed sediments are physically disturbed, buried organic carbon can re-enter the water column as carbon dioxide via remineralisation [8]. Remineralisation rates are affected by several factors, including disturbance intensity, depth of sediment disturbance, oxygen exposure time [9,10], the source of the organic matter [11,12], and its reactivity [13]. Carbon remineralisation also alters ocean chemistry through acidification [14]. It has the potential to impact atmospheric CO2 concentrations, by reducing the capacity of the ocean to absorb atmospheric carbon dioxide [14,15], or by increasing CO2 release to the atmosphere [16]. Shelf sea sediments, typically in waters less than 200 m deep, are particularly vulnerable to disturbance from human activities due to relative ease of access [17]. Quantifying the risk of human disturbance to seabed carbon stores has recently gained much scientific and management interest, mainly focussed on the bottom trawl fishing industry [13,14,16,18–20]. There are additional human activities that disturb shelf sea sediments [6], with limited understanding of their impacts on sedimentary carbon. This represents an obstacle to understanding and mitigating their climate impacts [17,21,22]. Dredging of ports, harbours, and navigational access channels (hereafter collectively referred to as port dredging) and marine aggregate extraction are extractive industries characterised by the removal, or redistribution, of sediment from the seabed using specialised dredging equipment. In the case of ports, sediments are dredged either via capital or maintenance dredging, with the extracted material generally disposed at-sea depending on national and international guidelines [23]. Capital dredging is typically undertaken ahead of engineering works (e.g., for port, dock, canal, and marina construction), whereas maintenance dredging ensures navigational depth and prevents siltation of ports and waterways. Mechanised steam dredgers were first built in Sunderland (UK) in 1797 [24], and ports such as Hamburg have been dredged since the 16th century [25]. Marine aggregate extraction generally targets coarse sediments, such as sands and gravels [26], that are used in the construction industry. Although an industry for marine aggregates extraction can be traced back to the 1910s in the United Kingdom, its expansion to large scale commercial operations took place in the 1960s [27]. The physical and biological impacts of marine aggregate extraction are relatively well documented in Europe [28–30], as are the biological impacts of maintenance dredging [31,32], but very little research has investigated the impacts of these industries on shelf sea carbon stores. As both industries are widespread an (...truncated)