Gao, Y.

Meysman, F.J.R.

Van de Velde, S.

Open Marine Archive

- 88 - 
 
 
The impact of dredging on the geochemical cycling in coastal 
ecosystems 
Van De Velde Sebastiaan
1
, Gao Yue
1
 and Meysman Filip
1 
1
 Department of Analytical, Environmental and Geochemistry, Vrije Universiteit Brussel (VUB), Pleinlaan 
2, 1050 Brussel, Belgium 
E-mail: sebastiaan.van.de.velde@vub.be  
 
The intensity of anthropogenic activity in the coastal ocean is rapidly increasing, and this puts more 
and more pressure on local marine ecosystems (Halpern et al., 2008). Industrial activities, such as 
bottom trawling and dredging, have a profound impact on the seafloor via the relocation and 
homogenization of the surface layer sediment (IADC/CEDA, 1997). Dredging is connected to the 
maintenance of man-made waterways and access channels to harbours, the construction of wind farms 
and coastal defence, as well as land reclamation. In the European Union alone, dredging results in the 
excavation of 200-250 million tons of sediment per year, of which ~80 % is redeposited in marine 
environment (EuDA annual report 2005), thus illustrating the large scale on which this operates in 
coastal waters. 
 
The coastal seafloor receives high amounts of organic carbon, which limits the oxygen penetration 
depth, and allows for the preservation and burial of organic carbon. This makes these sediments an 
essential carbon sink that couples the long- and short-term carbon cycle (Middelburg and Meysman, 
2007). Frequent dredging in coastal waters directly disturbs this carbon sink and thus could leave an 
anthropogenic fingerprint on the global carbon cycle. To date, the magnitude of this impact has 
however not been quantified. 
 
We investigated the sediment biogeochemistry at a field site in the shallow Southern North Sea, ~5 km 
offshore the Belgian coast (BCZ130, N 51°16.3’, E 2°54.3’) during 12 consecutive monthly campaigns 
over 2014. Unexpectedly, a major disturbance event took place between the May and June 2014 
sampling campaigns, which affected the upper ~15 cm of the sediment and had a major impact on the 
geochemical cycling. Evidence from both in situ data and model simulations suggest that this 
disturbance was caused by the deposition of a 15 cm thick layer of dredged harbour sediment. Our 
results show that this deposition event induced a reset of the geochemical cycling within the upper 
seafloor, which leads to an alternating sequence of electron acceptors, following the thermodynamic 
energy gain. It takes > 1 year for the mineralisation rates to return to the steady state.  This result 
implies that 1 - 2 depositions per year keeps the seafloor in a permanent transient state. The 
anthropogenic influence on the biogeochemistry of these coastal systems is likely larger than 
previously acknowledged. 
 
Keywords: dredging; carbon cycle; mineralisation; transient diagenesis 
 
References 
- Halpern B. S. et al. 2008. A global map of human impact on marine ecosystems. Science. 319:948–
952 
- International Association of Dredging Companies (IADC)/Central Dredging Association (CEDA). 1997. 
Environmental Aspects of Dredging. Guide 3 (Investigation, Interpretation and Impact). 
- Middelburg J. J. & Meysman F. J. R. 2007. Burial at Sea. Science. 316:1294–1295. 
  


The impact of dredging on the geochemical cycling in coastal ecosystems

Abstract

Similar works

Full text

Available Versions

Open Marine Archive