Effect of environmental factors (wave exposure and depth) and anthropogenic pressure in the C sink capacity of Posidonia oceanica meadows

Seagrass are among the most important natural carbon sinks on Earth with Posidonia oceanica (Mediterranean Sea) considered as the most relevant species. Yet, the number of direct measurements of organic carbon burial rates in P. oceanica is still scarce and the effect of local environmental factors remains largely unexplored. In addition, P. oceanica meadows are declining due to the increase in anthropogenic pressure in coastal areas during the last century. The aim of this study is to assess the recent carbon sink capacity of P. oceanica and particularly the effect of human pressure and two environmental factors, water depth and exposure to wave energy (based on a fetch index), on the carbon burial rate since 1900. We conducted an extensive survey of sediment cores in meadows distributed across a gradient of depth, fetch, and human pressure around The Balearic Islands. Sediment and carbon accumulation rates were obtained from 210Pb concentrations profiles. Top-30 centimeters carbon stocks (6.1 ± 1.4 kg C m−2) and burial rates (26 ± 6 g C m−2 yr1) varied up to fivefold across meadows. No significant effect of water depth in carbon burial rates was observed. Although fetch was significantly correlated with sediment mean grain size, confirming the effect of wave exposure in the patterns of sedimentation, fetch alone could not explain the differences in carbon burial rates among the meadows examined. Human pressure affected carbon burial rates, leading to increased rates since the onset of the rise in anthropogenic pressure, particularly so in sheltered meadows supporting high human pressure.

Mazarrasa I, Marbà N, Garcia-Orellana J, Masqué P, Arias-Ortiz A, et al. (2017) Effect of environmental factors (wave exposure and depth) and anthropogenic pressure in the C sink capacity of Posidonia oceanica meadows. Limnology and Oceanography. Available: http://dx.doi.org/10.1002/lno.10510.

We thank Regino Martınez and Fernando Lazaro for field work support and Laura Oliver for laboratory assistance. We thank the ferry company Balearia for supporting travel between islands. This study was funded by the EU FP7 projects Opera (contract number 308393), the project EstresX funded by the Spanish Ministry of Economy and Competitiveness (contract number CTM2012-32603). I.M. as supported by a Ph.D. scholarship of the Government of the Balearic Islands (Spain); AAO as supported by a Ph.D. grant of Obra Social “la Caixa”. JGO, AAO, and PM were partially funded by the Generalitat de Catalunya (MERS, 2014 SGR – 1356). This work is contributing to the ICTA ’Unit of Excellence’ (MinECo, MDM2015-0552).


Limnology and Oceanography


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