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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 13
Biogeosciences, 15, 4131-4145, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue: Assessing environmental impacts of deep-sea mining...

Biogeosciences, 15, 4131-4145, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 06 Jul 2018

Research article | 06 Jul 2018

Abyssal plain faunal carbon flows remain depressed 26 years after a simulated deep-sea mining disturbance

Tanja Stratmann1, Lidia Lins2,a, Autun Purser3, Yann Marcon3,b, Clara F. Rodrigues4, Ascensão Ravara4, Marina R. Cunha4, Erik Simon-Lledó5, Daniel O. B. Jones5, Andrew K. Sweetman6, Kevin Köser7, and Dick van Oevelen1 Tanja Stratmann et al.
  • 1NIOZ Royal Netherlands Institute for Sea Research, Department of Estuarine and Delta Systems, and Utrecht University, P.O. Box 140, 4400 AC Yerseke, the Netherlands
  • 2Marine Biology Research Group, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium
  • 3Deep Sea Ecology and Technology, Alfred Wegener Institute, Am Handelshafen 12, 27570 Bremerhaven, Germany
  • 4Departamento de Biologia & Centro de Estudos do Ambiente e do Mar (CESAM), Departamento de Biologia, Universidade de Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
  • 5National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton SO14 3ZH, UK
  • 6Marine Benthic Ecology, Biogeochemistry and In-situ Technology Research Group, The Lyell Centre for Earth and Marine Science and Technology, Heriot-Watt University, Edinburgh EH14 4AS, UK
  • 7GEOMAR Helmholtz Centre for Ocean Research, FE Marine Geosystems, Wischhofstr 1–3, 24148 Kiel, Germany
  • apresent address: Senckenberg Research Institute, Senckenberganlage 25, 60325 Frankfurt am Main, Germany
  • bpresent address: MARUM – Center for Marine Environmental Sciences, General Geology – Marine Geology, University of Bremen, 28359 Bremen, Germany

Abstract. Future deep-sea mining for polymetallic nodules in abyssal plains will negatively impact the benthic ecosystem, but it is largely unclear whether this ecosystem will be able to recover from mining disturbance and if so, to what extent and at what timescale. During the DISturbance and reCOLonization (DISCOL) experiment, a total of 22% of the seafloor within a 10.8km2 circular area of the nodule-rich seafloor in the Peru Basin (SE Pacific) was ploughed in 1989 to bury nodules and mix the surface sediment. This area was revisited 0.1, 0.5, 3, 7, and 26 years after the disturbance to assess macrofauna, invertebrate megafauna and fish density and diversity. We used this unique abyssal faunal time series to develop carbon-based food web models for each point in the time series using the linear inverse modeling approach for sediments subjected to two disturbance levels: (1) outside the plough tracks; not directly disturbed by plough, but probably suffered from additional sedimentation; and (2) inside the plough tracks. Total faunal carbon stock was always higher outside plough tracks compared with inside plough tracks. After 26 years, the carbon stock inside the plough tracks was 54% of the carbon stock outside plough tracks. Deposit feeders were least affected by the disturbance, with modeled respiration, external predation, and excretion rates being reduced by only 2.6% inside plough tracks compared with outside plough tracks after 26 years. In contrast, the respiration rate of filter and suspension feeders was 79.5% lower in the plough tracks after 26 years. The total system throughput (T..), i.e., the total sum of modeled carbon flows in the food web, was higher throughout the time series outside plough tracks compared with the corresponding inside plough tracks area and was lowest inside plough tracks directly after the disturbance (8.63 × 10−3±1.58 × 10−5mmolCm−2d−1). Even 26 years after the DISCOL disturbance, the discrepancy of T.. between outside and inside plough tracks was still 56%. Hence, C cycling within the faunal compartments of an abyssal plain ecosystem remains reduced 26 years after physical disturbance, and a longer period is required for the system to recover from such a small-scale sediment disturbance experiment.

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Short summary
Extraction of polymetallic nodules will have negative impacts on the deep-sea ecosystem, but it is not known whether the ecosystem is able to recover from them. Therefore, in 1989 a sediment disturbance experiment was conducted in the Peru Basin to mimic deep-sea mining. Subsequently, the experimental site was re-visited 5 times to monitor the recovery of fauna. We developed food-web models for all 5 time steps and found that, even after 26 years, carbon flow in the system differs significantly.
Extraction of polymetallic nodules will have negative impacts on the deep-sea ecosystem, but it...