Can mud (silt and clay) concentration be used to predict soil organic carbon content within seagrass ecosystems?
- 1School of Natural Sciences & Centre for Marine Ecosystems Research, Faculty of Health, Engineering and Science, Edith Cowan University, Joondalup, 6027, Western Australia
- 2The UWA Oceans Institute, The University of Western Australia, Crawley, WA, Australia
- 3Centro de Estudios Avanzados de Blanes, Consejo Superior de Investigaciones Científicas, Blanes, 17300, Spain
- 4King Abdullah University of Science and Technology (KAUST), Red Sea Research Center (RSRC), Thuwal, 23955-6900, Saudi Arabia
- 5The School of Plant Biology, The University of Western Australia, Crawley, WA, Australia
- 6GRC Geociències Marines, Departament de Dinàmica de la Terra i de l'Oceà, Universitat de Barcelona, Barcelona, Spain
- 7Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER), James Cook University, Cairns QLD 4870, Australia
- 8CSIRO, EcoSciences Precinct – Dutton Park 41 Boggo Road Dutton Park QLD 4102, Australia
- 9Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Burwood, Victoria 3125, Australia
- 10Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Broadway, New South Wales 2007, Australia
Abstract. The emerging field of blue carbon science is seeking cost-effective ways to estimate the organic carbon content of soils that are bound by coastal vegetated ecosystems. Organic carbon (Corg) content in terrestrial soils and marine sediments has been correlated with mud content (i.e., silt and clay, particle sizes < 63 µm), however, empirical tests of this theory are lacking for coastal vegetated ecosystems. Here, we compiled data (n = 1345) on the relationship between Corg and mud contents in seagrass ecosystems (79 cores) and adjacent bare sediments (21 cores) to address whether mud can be used to predict soil Corg content. We also combined these data with the δ13C signatures of the soil Corg to understand the sources of Corg stores. The results showed that mud is positively correlated with soil Corg content only when the contribution of seagrass-derived Corg to the sedimentary Corg pool is relatively low, such as in small and fast-growing meadows of the genera Zostera, Halodule and Halophila, and in bare sediments adjacent to seagrass ecosystems. In large and long-living seagrass meadows of the genera Posidonia and Amphibolis there was a lack of, or poor relationship between mud and soil Corg content, related to a higher contribution of seagrass-derived Corg to the sedimentary Corg pool in these meadows. The relatively high soil Corg contents with relatively low mud contents (e.g., mud-Corg saturation) in bare sediments and Zostera, Halodule and Halophila meadows was related to significant allochthonous inputs of terrestrial organic matter, while higher contribution of seagrass detritus in Amphibolis and Posidonia meadows disrupted the correlation expected between soil Corg and mud contents. This study shows that mud is not a universal proxy for blue carbon content in seagrass ecosystems, and therefore should not be applied generally across all seagrass habitats. Mud content can only be used as a proxy to estimate soil Corg content for scaling up purposes when opportunistic and/or low biomass seagrass species (i.e., Zostera, Halodule and Halophila) are present (explaining 34 to 91 % of variability), and in bare sediments (explaining 78 % of the variability). The results obtained could enable robust scaling up exercises at a low cost as part of blue carbon stock assessments.