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Blue carbon ecosystems sequester and store a larger mass of organic carbon per unit area than many other vegetated ecosystems, with most being stored in the soil. Understanding the fine-scale drivers of variability in blue carbon soil stocks is important for supporting accurate carbon accounting and effective management of saltmarsh and mangrove habitats for carbon abatement. Here, we investigate the influence of local- and regional-scale environmental factors on soil organic carbon stocks using a case study from South Australia. We sampled 74 soil cores from mangrove, intertidal saltmarsh and supratidal saltmarsh sites where we also recorded precise elevation and vegetation data. Using a Bayesian mixed-effects regression approach, we modelled soil organic carbon stocks as a function of multiple environmental variables. The best model (Bayes R2 = 0.82) found that distance to the nearest tidal creek, vegetation type and soil texture significantly affected soil organic carbon stocks. Coarser soils with higher sand content had lower stocks, while finer-grained, clay-dominated soils had greater stocks. Mangroves had significantly greater stocks than intertidal saltmarshes and stocks were higher in sites closer to tidal creeks, highlighting the important role that local tidal creek systems play in sediment and water transport. This study’s findings are based on a broader range of local environmental factors than are usually considered in blue carbon models and increase our understanding and ability to predict site-level soil organic blue carbon stocks. The results emphasise the potential for organic carbon stocks to vary at local scales; the ability to predict this using appropriate environmental datasets; and the importance of accounting for local organic carbon stock variability when selecting sites for blue carbon-focussed restoration or conservation actions that aim to achieve carbon abatement.
Blue carbon ecosystems sequester and store a larger mass of organic carbon per unit area than many other vegetated ecosystems, with most being stored in the soil. Understanding the fine-scale drivers of variability in blue carbon soil stocks is important for supporting accurate carbon accounting and effective management of saltmarsh and mangrove habitats for carbon abatement. Here, we investigate the influence of local- and regional-scale environmental factors on soil organic carbon stocks using a case study from South Australia. We sampled 74 soil cores from mangrove, intertidal saltmarsh and supratidal saltmarsh sites where we also recorded precise elevation and vegetation data. Using a Bayesian mixed-effects regression approach, we modelled soil organic carbon stocks as a function of multiple environmental variables. The best model (Bayes R2 = 0.82) found that distance to the nearest tidal creek, vegetation type and soil texture significantly affected soil organic carbon stocks. Coarser soils with higher sand content had lower stocks, while finer-grained, clay-dominated soils had greater stocks. Mangroves had significantly greater stocks than intertidal saltmarshes and stocks were higher in sites closer to tidal creeks, highlighting the important role that local tidal creek systems play in sediment and water transport. This study’s findings are based on a broader range of local environmental factors than are usually considered in blue carbon models and increase our understanding and ability to predict site-level soil organic blue carbon stocks. The results emphasise the potential for organic carbon stocks to vary at local scales; the ability to predict this using appropriate environmental datasets; and the importance of accounting for local organic carbon stock variability when selecting sites for blue carbon-focussed restoration or conservation actions that aim to achieve carbon abatement.
Coastal vegetated ecosystems are acknowledged for their capacity to sequester organic carbon (OC), known as blue C. Yet, blue C global accounting is incomplete, with major gaps in southern hemisphere data. It also shows a large variability suggesting that the interaction between environmental and biological drivers is important at the local scale. In southwest Atlantic salt marshes, to account for the space occupied by crab burrows, it is key to avoid overestimates. Here we found that southern southwest Atlantic salt marshes store on average 42.43 (SE = 27.56) Mg OC·ha−1 (40.74 (SE = 2.7) in belowground) and bury in average 47.62 g OC·m−2·yr−1 (ranging from 7.38 to 204.21). Accretion rates, granulometry, plant species and burrowing crabs were identified as the main factors in determining belowground OC stocks. These data lead to an updated global estimation for stocks in salt marshes of 185.89 Mg OC·ha−1 (n = 743; SE = 4.92) and a C burial rate of 199.61 g OC·m−2·yr−1 (n = 193; SE = 16.04), which are lower than previous estimates.
Coastal saltmarshes are found globally, yet are 25%–50% reduced compared with their historical cover. Restoration is incentivised by the promise that marshes are efficient storers of ‘blue’ carbon, although the claim lacks substantiation across global contexts. We synthesised data from 431 studies to quantify the benefits of saltmarsh restoration to carbon accumulation and greenhouse gas uptake. The results showed global marshes store approximately 1.41–2.44 Pg carbon. Restored marshes had very low greenhouse gas (GHG) fluxes and rapid carbon accumulation, resulting in a mean net accumulation rate of 64.70 t CO2e ha−1 year−1. Using this estimate and potential restoration rates, we find saltmarsh regeneration could result in 12.93–207.03 Mt CO2e accumulation per year, offsetting the equivalent of up to 0.51% global energy‐related CO2 emissions—a substantial amount, considering marshes represent <1% of Earth's surface. Carbon accumulation rates and GHG fluxes varied contextually with temperature, rainfall and dominant vegetation, with the eastern coasts of the USA and Australia particular hotspots for carbon storage. While the study reveals paucity of data for some variables and continents, suggesting need for further research, the potential for saltmarsh restoration to offset carbon emissions is clear. The ability to facilitate natural carbon accumulation by saltmarshes now rests principally on the action of the management‐policy community and on financial opportunities for supporting restoration.
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