Department of Biology, Faculty of Marine and Environmental Sci...

Coastal development and climate change are sparking growing concern about the vulnerability of the organic carbon OC stocks in marine sediments to remineralization especially in high threaten coastal ecosystems like seagrass meadows Uncertainties still exist regarding the role played by hydrodynamics seagrass canopies and sediment properties in OC resuspension and remineralization A set of laboratory experiments were conducted to assess for the first time the mechanisms by which the particulate and dissolved organic carbon POC and DOC may be released and remineralized under hydrodynamic conditions i e unidirectional and oscillatory flows in two eelgrass densities and sediments properties i e grain size and OC content After a gradually increase in hydrodynamic forces our results demonstrated that the presence of eelgrass reduced sediment erosion and OC loss in high-density canopies while low-density canopies promote OC resuspension on average 1 8-fold higher than high-density canopies We also demonstrated that unidirectional and oscillatory flows released similar DOC from surface sediments on average 15 5 1 4 and 18 4 1 8 g m-2 respectively whereas oscillatory flow released significantly more POC than unidirectional flows from 10 8 1 1 to 32 1 5 6 g m-2 for unidirectional and oscillatory flows respectively POC and DOC released was strongly influenced by both seagrass meadow structure i e lower eelgrass density and shoot area and sediment properties i e lower mud and higher sediment water content We found that although 74 of OC in upper sediments was remineralized within 30 days a relatively high amount of OC in high-density canopies is recalcitrant highlighting its potential for the formation of blue carbon deposits This study highlights the vulnerability of OC deposits in seagrass sediments to resuspension if the meadow is degraded and or the climate change yield stronger storms which could potentially weaken the seagrass meadows service as blue carbon ecosystem in the future Copyright 2023 The Authors Published by Elsevier B V All rights reserved

Department of Biology, Faculty of Marine and Environmental Sciences, University of Cadiz, International Campus of Excellence of the Sea (CEI·MAR), 11510 Puerto Real, Cádiz, Spain.

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Loss of POC and DOC on seagrass sediments by hydrodynamics.