Contributions of the direct supply of belowground seagrass detritus and trapping of suspended organic matter to the sedimentary organic carbon stock in seagrass meadows
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Published:2018-07-03
Issue:13
Volume:15
Page:4033-4045
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Tanaya TokoORCID, Watanabe KentaORCID, Yamamoto Shoji, Hongo ChukiORCID, Kayanne Hajime, Kuwae TomohiroORCID
Abstract
Abstract. Carbon captured by marine living organisms is called “blue carbon”, and
seagrass meadows are a dominant blue carbon sink. However, our knowledge of
how seagrass increases sedimentary organic carbon (OC) stocks is limited. We
investigated two pathways of OC accumulation: trapping of organic matter in
the water column and the direct supply of belowground seagrass detritus. We
developed a new type of box corer to facilitate the retrieval of intact cores
that preserve the structures of both sediments (including coarse sediments
and dead plant structures) and live seagrasses. We measured seagrass density,
total OC mass (OCtotal) (live seagrass OC biomass
(OCbio) + sedimentary OC mass (OCsed)), and the
stable carbon isotope ratio (δ13C) of OCsed and its
potential OC sources at Thalassia hemprichii dominated back-reef and
Enhalus acoroides dominated estuarine sites in the tropical
Indo-Pacific region. At points with vegetation, OCbio accounted
for 25 % and OCsed for 75 % of OCtotal; this
contribution of OCbio to OCtotal is higher than in
globally compiled data. Belowground detritus accounted for ∼ 90 %
of the OC mass of dead plant structures (> 2 mm in size)
(OCdead). At the back-reef site, belowground seagrass biomass,
OCdead, and δ13C of OCsed (δ13Csed) were positively correlated with OCsed,
indicating that the direct supply of belowground seagrass detritus is a major
mechanism of OCsed accumulation. At the estuarine site,
aboveground seagrass biomass was positively correlated with OCsed
but δ13Csed did not correlate with OCsed,
indicating that trapping of suspended OC by seagrass leaves is a major
mechanism of OCsed accumulation there. We inferred that the
relative importance of these two pathways may depend on the supply
(productivity) of belowground biomass. Our results indicate that belowground
biomass productivity of seagrass meadows, in addition to their aboveground
morphological complexity, is an important factor controlling their OC stock.
Consideration of this factor will improve global blue carbon estimates.
Funder
Japan Society for the Promotion of Science
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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