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Sedimentary Factors are Key Predictors of Carbon Storage in SE Australian Saltmarshes

Abstract

Although coastal vegetated ecosystems are widely recognised as important sites of long-term carbon (C) storage, substantial spatial variability exists in quantifications of these ‘blue C’ stocks. To better understand the factors behind this variability we investigate the relative importance of geomorphic and vegetation attributes to variability in the belowground C stocks of saltmarshes in New South Wales (NSW), southeast Australia. Based on the analysis of over 140 sediment cores, we report mean C stocks in the surface metre of sediments (mean ± SE = 164.45 ± 8.74 Mg C ha−1) comparable to global datasets. Depth-integrated stocks (0–100 cm) were more than two times higher in fluvial (226.09 ± 12.37 Mg C ha−1) relative to marine (104.54 ± 7.11) geomorphic sites, but did not vary overall between rush and non-rush vegetation structures. More specifically, sediment grain size was a key predictor of C density, which we attribute to the enhanced C preservation capacity of fine sediments and/or the input of stable allochthonous C to predominantly fine-grained, fluvial sites. Although C density decreased significantly with sediment depth in both geomorphic settings, the importance of deep C varied substantially between study sites. Despite modest spatial coverage, NSW saltmarshes currently hold approximately 1.2 million tonnes of C in the surface metre of sediment, although more C may have been returned to the atmosphere through habitat loss over the past approximately 200 years. Our findings highlight the suitability of using sedimentary classification to predict blue C hotspots for targeted conservation and management activities to reverse this trend.

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Acknowledgements

Frederic Cadera is thanked for assistance with field sampling and sample preparation. Field collections were undertaken in accordance with NSW Office of Environment and Heritage scientific licence SL101217 and NSW Department of Primary Industries Scientific Permit P13/0058-1.0. We also thank NSW National Parks and Wildlife Service for supporting access to conservation reserves for fieldwork. This research was supported by the CSIRO Coastal Carbon Cluster and South East Local Land Services. PM was supported by an Australian Research Council DECRA Fellowship (DE130101084).

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Correspondence to Jeffrey J. Kelleway.

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All authors contributed to the design of the study and writing of the paper. JJK performed research and analysed data.

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Kelleway, J.J., Saintilan, N., Macreadie, P.I. et al. Sedimentary Factors are Key Predictors of Carbon Storage in SE Australian Saltmarshes. Ecosystems 19, 865–880 (2016). https://doi.org/10.1007/s10021-016-9972-3

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Keywords

  • carbon sequestration
  • blue carbon
  • saltmarsh
  • salt marsh
  • spatial variability
  • geomorphic setting
  • ecosystem services
  • tidal marshes