Physical Disturbance by Bottom Trawling Suspends Particulate Matter and Alters Biogeochemical Processes on and Near the Seafloor

• DOI: 10.3389/fmars.2021.683331
• Publication Date: 2021-08-25T08:29:38Z
• Authors: Clare Bradshaw; Martin Jakobsson; Volker Brüchert; Stefano Bonaglia; Carl-Magnus Mörth; Julia Muchowski; Christian Stranne; Mattias Sköld
• Keywords: Bottom trawling; Biogeochemical Cycle; Seabed; Dredging

Bottom trawling is known to affect benthic faunal communities but its effects on sediment suspension and seabed biogeochemistry are less well described. In addition, few studies have been carried out in the Baltic Sea, despite decades of this unique brackish environment frequent occurrence areas where hypoxia low variable salinity already act as ecosystem stressors. We measured physical biogeochemical impacts an otter trawl a muddy seabed. Multibeam bathymetry revealed 36 m-wide track, comprising parallel furrows piles caused by doors shallower grooves from groundgear, that displaced 1,000 m 3 (500 t) suspended 9.5 t per km track. The had effect than rest gear terms total mass 2 5× displacement 2× effect, due their greater penetration hydrodynamic drag. spread >1 away over following 3–4 days, creating 5–10 thick layer turbid bottom water. Turbidity reached 4.3 NTU (7 mgDW L –1 ), 550 20 h post-trawling. Particulate Al, Ti, Fe, P, Mn were correlated with spatio-temporal pattern suspension. There was pulse dissolved N, height 10 above within hundred meters Dissolved methane concentrations elevated water for at least h. Sediment door track still perturbed after 48 h, decreased oxygen depth nutrient fluxes across sediment-water interface. These results clearly show trawling, both topography (on scale years) particle days-weeks). Alterations processes suggest that, frequent, may not time recover between disturbance events turbidity persist, even outside trawled area.