Anthropogenic disturbance keeps the coastal seafloor biogeochemistry in a transient state

Sebastiaan Van De Velde,Vera Van Lancker,Filip J R Meysman,Silvia Hidalgo-Martinez,William M Berelson

doi:10.1038/s41598-018-23925-y

Abstract

Coastal sediments and continental shelves play a crucial role in global biogeochemistry, as they form the prime site of organic carbon burial. Bottom trawling and dredging are known to increasingly impact the coastal seafloor through relocation and homogenisation of sediments, yet little is known about the effects of such anthropogenic sediment reworking on the overall cycling of carbon and other elements within the coastal seafloor. Here, we document the transient recovery of the seafloor biogeochemistry after an in situ disturbance. Evidence from pore-water data and model simulations reveal a short-term increase in the overall carbon mineralisation rate, as well as a longer-term shift in the redox pathways of organic matter mineralisation, favouring organoclastic sulphate reduction over methane formation. This data suggests that anthropogenic sediment reworking could have a sizeable impact on the carbon cycle in cohesive sediments on continental shelves. This imprint will increase in the near future, along with the growing economic exploitation of the coastal ocean.

Highlights

The human imprint on the seafloor has rapidly increased in recent times[1]
Little is known about the direct impact of bottom trawling and dredging on the cycling of carbon and other major elements within the coastal seafloor, which is a major knowledge gap, as coastal sediments and continental shelves play a crucial role in the global carbon cycle[17,18,19]
Lack of data regarding the effects of bottom trawling and dredging on coastal seafloor biogeochemistry directly translates into uncertainties in global carbon budgets and hampers our understanding of the anthropogenic influence on the carbon cycle[17,18]

Summary

Materials and Methods

Pore-water samples were analysed for the DIC, nutrients (NH4+, PO43−), dissolved Fe, dissolved Mn and sulphate (SO42−). Samples for major cation analysis (dissolved Fe, dissolved Mn) were fixed with 50 μL per mL of sub-boiled distilled HNO3 (65%) and preserved at 4 °C Prior to analysis, these preserved samples were diluted 50 times with a standard matrix solution containing 35% artificial seawater, 2% HNO3 and 0.2 mg L−1 Ytterbium as an internal standard[29]. Nutrient samples (NH4+, PO43−) were fixed with 100 μL per mL H2SO4 (1 M) to prevent the oxidation and flocculation of reduced iron compounds, diluted 25 times with a low nutrient seawater matrix solution, and analysed by a SEAL QuAAtro segmented flow analyzer[31]. Quality assurance involved regular analysis of Certified Reference Materials (CRM) which was obtained from the Scripps Institution of Oceanography (batch 140)[33]

Results and Discussion

Author Contributions

Additional Information