Articles | Volume 13, issue 15
https://doi.org/10.5194/bg-13-4581-2016
https://doi.org/10.5194/bg-13-4581-2016
Research article
 | 
15 Aug 2016
Research article |  | 15 Aug 2016

Key biogeochemical factors affecting soil carbon storage in Posidonia meadows

Oscar Serrano, Aurora M. Ricart, Paul S. Lavery, Miguel Angel Mateo, Ariane Arias-Ortiz, Pere Masque, Mohammad Rozaimi, Andy Steven, and Carlos M. Duarte

Abstract. Biotic and abiotic factors influence the accumulation of organic carbon (Corg) in seagrass ecosystems. We surveyed Posidonia sinuosa meadows growing in different water depths to assess the variability in the sources, stocks and accumulation rates of Corg. We show that over the last 500 years, P. sinuosa meadows closer to the upper limit of distribution (at 2–4 m depth) accumulated 3- to 4-fold higher Corg stocks (averaging 6.3 kg Corg m−2) at 3- to 4-fold higher rates (12.8 g Corg m−2 yr−1) compared to meadows closer to the deep limits of distribution (at 6–8 m depth; 1.8 kg Corg m−2 and 3.6 g Corg m−2 yr−1). In shallower meadows, Corg stocks were mostly derived from seagrass detritus (88 % in average) compared to meadows closer to the deep limit of distribution (45 % on average). In addition, soil accumulation rates and fine-grained sediment content (< 0.125 mm) in shallower meadows (2.0 mm yr−1 and 9 %, respectively) were approximately 2-fold higher than in deeper meadows (1.2 mm yr−1 and 5 %, respectively). The Corg stocks and accumulation rates accumulated over the last 500 years in bare sediments (0.6 kg Corg m−2 and 1.2 g Corg m−2 yr−1) were 3- to 11-fold lower than in P. sinuosa meadows, while fine-grained sediment content (1 %) and seagrass detritus contribution to the Corg pool (20 %) were 8- and 3-fold lower than in Posidonia meadows, respectively. The patterns found support the hypothesis that Corg storage in seagrass soils is influenced by interactions of biological (e.g., meadow productivity, cover and density), chemical (e.g., recalcitrance of Corg stocks) and physical (e.g., hydrodynamic energy and soil accumulation rates) factors within the meadow. We conclude that there is a need to improve global estimates of seagrass carbon storage accounting for biogeochemical factors driving variability within habitats.

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Short summary
The recent focus on carbon (C) trading has intensified interest in "Blue Carbon" – C sequestered by coastal vegetation. However, the factors influencing C storage are poorly understood. The patterns found in this study support that C storage in Posidonia seagrass soils is influenced by interactions of biological, chemical and physical factors within the meadow. We conclude that there is a need to improve global estimates accounting for biogeochemical factors driving variability within habitats.
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