Preprints
https://doi.org/10.5194/bg-2021-159
https://doi.org/10.5194/bg-2021-159

  01 Jul 2021

01 Jul 2021

Review status: this preprint is currently under review for the journal BG.

Mangrove sediment organic carbon storage and sources in relation to forest age and position along a deltaic salinity gradient

Rey Harvey Suello1, Simon Lucas Hernandez1,5, Steven Bouillon2, Jean-Philippe Belliard1, Luis Dominguez-Granda3, Marijn Van de Broek4, Andrea Mishell Rosado Moncayo3, John Ramos Veliz3, Karem Pollette Ramirez3, Gerard Govers2, and Stijn Temmerman1 Rey Harvey Suello et al.
  • 1University of Antwerp, Ecosystem Management Research Group
  • 2Katholieke Universiteit Leuven, Division of Soil and Water Management
  • 3Escuela Superior Politecnica del Litoral, Department of Sustainable Water Management
  • 4Swiss Federal Institute of Technology, Department of Environmental Systems Science
  • 5Ghent University, Laboratory of Environmental Toxicology and Aquatic Ecology

Abstract. Mangroves are widely recognised as key ecosystems for climate change mitigation as they capture and store significant amounts of sediment organic carbon (SOC). Yet, there is incomplete knowledge on how sources of SOC and their differential preservation vary between mangrove sites in relation to environmental gradients. To address this, sediment depth profiles were sampled from mangrove sites ranging from river-dominated to marine-dominated sites and including old and young mangrove sites, in the Guayas delta (Ecuador). The stable carbon isotope ratios (δ13C) and the elemental composition (OC%, C : N) of sediment profiles, local vegetation (i.e., autochthonous carbon) and externally-supplied suspended particulate matter (i.e., allochthonous carbon) were obtained to assess variations in the amount and sources of SOC at different locations throughout the delta. In general, across all sites, we found increasing SOC contents and stocks are associated with decreasing δ13C and increasing C / N ratios, indicating that SOC stocks and sources are intrinsically related. The SOC stocks (down to 0.64 m deep profiles) are significantly lower in young mangrove sites (46–55 Mg C ha−1) than in old sites (78–92 Mg C ha−1). The SOC in the young mangrove sites is mainly of allochthonous origin (estimated on average at 79 %) whereas in the old sites there is a slight dominance of autochthonous OC (on average 59 %). Moreover, from river- to marine-dominated sites, a pattern was found of increasing SOC stocks and increasing autochthonous SOC contribution. These observed differences along the two studied gradients are hypothesized to be mainly driven by (1) expected higher sedimentation rates in the river-dominated and lower-elevation younger sites, thereby “diluting” the SOC content and decreasing the relative autochthonous contribution; and (2) potential differences in preservation of the different SOC sources. Our finding of high contributions of allochthonous SOC, especially in young mangroves, implies that this carbon is not originating from CO2 sequestration by the mangrove ecosystem itself, but is externally supplied from other terrestrial, marine or estuarine ecosystems. We argue that accounting for lower SOC stocks and higher contribution of allochthonous SOC in young and river-dominated mangrove sites, as compared to old and marine-dominant sites, is particularly relevant for designing and valuing nature-based climate mitigation programs based on mangrove reforestation.

Rey Harvey Suello et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-159', Anonymous Referee #1, 09 Aug 2021
    • AC1: 'Reply on RC1', Rey Harvey Suello, 11 Aug 2021
    • AC2: 'Reply on RC1', Rey Harvey Suello, 16 Nov 2021
  • RC2: 'Comment on bg-2021-159', G. N Nayak, 08 Oct 2021
    • AC3: 'Reply on RC2', Rey Harvey Suello, 16 Nov 2021
  • RC3: 'Comment on bg-2021-159', Anonymous Referee #3, 18 Oct 2021
    • AC4: 'Reply on RC3', Rey Harvey Suello, 16 Nov 2021

Rey Harvey Suello et al.

Rey Harvey Suello et al.

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Short summary
This research shows strong indications that the age of the mangrove forest and its position from upstream to downstream along a delta play a vital role in the amount and sources of carbon stored in the mangrove sediments. Our findings also imply that carbon capture by the mangrove ecosystem itself contributes only partly and relatively little to long-term SOC storage. This finding is particularly relevant for budgeting the potential of mangrove ecosystems to mitigate climate change.
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