Soil carbon stocks vary across geomorphic settings in Australian temperate tidal marsh ecosystems

Tidal marshes rank among the ecosystems with the highest capacity to sequester and store organic carbon (Corg) on earth. To inform conservation of coastal vegetated ecosystems for climate change mitigation, this study investigated the factors driving variability in carbon storage. We estimated soil Corg stocks in tidal marshes across temperate Western Australia and assessed differences among geomorphic settings (marine and fluvial deltas, and mid-estuary) and vegetation type (Sarcocornia quinqueflora and Juncus kraussii) linked to soil biogeochemistry. Soil Corg stocks within fluvial and mid-estuary settings were significantly higher (209 ± 14 and 211 ± 20 Mg Corg ha−1, respectively; 1-m-thick soils) than in marine counterparts (156 ± 12 Mg Corg ha−1), which can be partially explained by higher preservation of soil Corg in fluvial and mid-estuary settings rich in fine-grained ( \u3c 0.063 mm) sediments (49 ± 3% and 47 ± 4%, respectively) compared to marine settings (23 ± 4%). Soil Corg stocks were not significantly different between S. quinqueflora and J. kraussii marshes (185 ± 13 and 202 ± 13 Mg Corg ha−1, respectively). The higher contribution of tidal marsh plus supratidal vegetation in fluvial (80%) and intermediate (76%) compared to marine (57%) settings further explains differences in soil Corg stocks. The estimated soil Corg stocks in temperate Western Australia’s tidal marshes (57 Tg Corg within ~ 3000 km2 extent) correspond to about 2% of worldwide tidal marsh soil Corg stocks. The results obtained identify global drivers of soil Corg storage in tidal marshes and can be used to target hot spots for climate change mitigation based on tidal marsh conservation

Comparison of marine macrophytes for their contributions to blue carbon sequestration

Many marine ecosystems have the capacity for long-term storage of organic carbon (C) in what are termed "blue carbon" systems. While blue carbon systems (saltmarsh, mangrove, and seagrass) are efficient at long-term sequestration of organic carbon (C), much of their sequestered C may originate from other (allochthonous) habitats. Macroalgae, due to their high rates of production, fragmentation, and ability to be transported, would also appear to be able to make a significant contribution as C donors to blue C habitats. In order to assess the stability of macroalgal tissues and their likely contribution to long-term pools of C, we applied thermogravimetric analysis (TGA) to 14 taxa of marine macroalgae and coastal vascular plants. We assessed the structural complexity of multiple lineages of plant and tissue types with differing cell wall structures and found that decomposition dynamics varied significantly according to differences in cell wall structure and composition among taxonomic groups and tissue function (photosynthetic vs. attachment). Vascular plant tissues generally exhibited greater stability with a greater proportion of mass loss at temperatures > 300 degrees C (peak mass loss -320 degrees C) than macroalgae (peak mass loss between 175-300 degrees C), consistent with the lignocellulose matrix of vascular plants. Greater variation in thermogravimetric signatures within and among macroalgal taxa, relative to vascular plants, was also consistent with the diversity of cell wall structure and composition among groups. Significant degradation above 600 degrees C for some macroalgae, as well as some belowground seagrass tissues, is likely due to the presence of taxon-specific compounds. The results of this study highlight the importance of the lignocellulose matrix to the stability of vascular plant sources and the potentially significant role of refractory, taxon-specific compounds (carbonates, long-chain lipids, alginates, xylans, and sulfated polysaccharides) from macroalgae and seagrasses for their long-term sedimentary C storage. This study shows that marine macroalgae do contain refractory compounds and thus may be more valuable to long-term carbon sequestration than we previously have considered

Saltmarsh of the Parramatta River-Sydney Harbour: determination of cover and species composition including comparison of API and pedestrian survey

In 2004 coastal saltmarsh was listed as an Endangered Ecological Community under the New South Wales Threatened Species Conservation Act, but more information on the ecology of saltmarsh species as well as accurate maps of the cover of saltmarsh are needed. Large scale maps produced in the early 1980s and the mid 2000s were based on air photo interpretation with follow-up field checks, but to determine the ability of air photos to detect small patches of coastal saltmarsh, a pedestrian survey along the foreshore of the Parramatta River-Sydney Harbour estuary (33° 53’S; 151° 13’E) was commissioned. Ground-truth activity was partitioned into three levels of intensity. At the greatest level of intensity, many small patches obscured in the air photos by (mainly mangrove) canopy cover were resolved and joined to reveal larger patches of saltmarsh. Compared to the earlier maps these areas are considered to increase the total area of existing saltmarsh, but they also may in fact be areas of saltmarsh that have been recently invaded by mangroves, and ultimately, through shading and competition result in the loss of the saltmarsh species at these sites. Another 609 patches not seen on the air photos were located. The pedestrian survey located 757 saltmarsh patches (70% of these were less than 100 m2 in area) with a total area of 37.3 ha. Parramatta River, relative to the Lane Cove River, Middle Harbour Creek and Sydney Harbour, supports the most numerous and extensive patches: 461 patches (61% by number), 29 ha (78% by area). Most of the patches of saltmarsh (60%), as well as most of their area (76%), are located in the most upstream Riverine Channel geomorphic zone of the Parramatta River, followed by downstream zones Fluvial Delta and Central Mud Basin. The fewest patches (14) and smallest area (0.04ha) were in the Marine Tidal Delta. The ‘conservation ‘sensitive’ species as well as some of the weed species also appeared to be restricted to the upper and middle parts of the estuary. API is useful for broad assessments of estuarine saltmarsh, but pedestrian survey is needed to provide the finer scale detail necessary to locate small patches and to identify species composition especially for rare or weed species

Can we manage coastal ecosystems to sequester more blue carbon?

© The Ecological Society of America To promote the sequestration of blue carbon, resource managers rely on best-management practices that have historically included protecting and restoring vegetated coastal habitats (seagrasses, tidal marshes, and mangroves), but are now beginning to incorporate catchment-level approaches. Drawing upon knowledge from a broad range of environmental variables that influence blue carbon sequestration, including warming, carbon dioxide levels, water depth, nutrients, runoff, bioturbation, physical disturbances, and tidal exchange, we discuss three potential management strategies that hold promise for optimizing coastal blue carbon sequestration: (1) reducing anthropogenic nutrient inputs, (2) reinstating top-down control of bioturbator populations, and (3) restoring hydrology. By means of case studies, we explore how these three strategies can minimize blue carbon losses and maximize gains. A key research priority is to more accurately quantify the impacts of these strategies on atmospheric greenhouse-gas emissions in different settings at landscape scales

Blue carbon as a natural climate solution

Blue carbon ecosystems (BCEs), including mangrove forests, seagrass meadows and tidal marshes, store carbon and provide co-benefits such as coastal protection and fisheries enhancement. Blue carbon sequestration has therefore been suggested as a natural climate solution. In this Review, we examine the potential for BCEs to act as carbon sinks and the opportunities to protect or restore ecosystems for this function. Globally, BCEs are calculated to store \u3e 30,000 Tg C across ~185 million ha, with their conservation potentially avoiding emissions of 304 (141–466) Tg carbon dioxide equivalent (CO2e) per year. Potential BCE restoration has been estimated in the range of 0.2–3.2 million ha for tidal marshes, 8.3–25.4 million ha for seagrasses and 9–13 million ha for mangroves, which could draw down an additional 841 (621–1,064) Tg CO2e per year by 2030, collectively amounting to ~3% of global emissions (based on 2019 and 2020 global annual fossil fuel emissions). Mangrove protection and/or restoration could provide the greatest carbon-related benefits, but better understanding of other BCEs is needed. BCE destruction is unlikely to stop fully, and not all losses can be restored. However, engineering and planning for coastal protection offer opportunities for protection and restoration, especially through valuing co-benefits. BCE prioritization is potentially a cost-effective and scalable natural climate solution, but there are still barriers to overcome before blue carbon project adoption will become widespread

Carbon sequestration by Australian tidal marshes

Australia's tidal marshes have suffered significant losses but their recently recognised importance in CO2 sequestration is creating opportunities for their protection and restoration. We compiled all available data on soil organic carbon (OC) storage in Australia's tidal marshes (323 cores). OC stocks in the surface 1 m averaged 165.41 (SE 6.96) Mg OC ha-1 (range 14-963 Mg OC ha-1). The mean OC accumulation rate was 0.55 ± 0.02 Mg OC ha-1 yr -1. Geomorphology was the most important predictor of OC stocks, with fluvial sites having twice the stock of OC as seaward sites. Australia's 1.4 million hectares of tidal marshes contain an estimated 212 million tonnes of OC in the surface 1 m, with a potential CO2 -equivalent value of $USD7.19 billion. Annual sequestration is 0.75 Tg OC yr -1, with a CO2 -equivalent value of$USD28.02 million per annum. This study provides the most comprehensive estimates of tidal marsh blue carbon in Australia, and illustrates their importance in climate change mitigation and adaptation, acting as CO2 sinks and buffering the impacts of rising sea level. We outline potential further development of carbon offset schemes to restore the sequestration capacity and other ecosystem services provided by Australia tidal marshes

Hot spots and hot moments in seagrass 'blue carbon' science

When seagrass meadows are destroyed, what happens to the 'blue carbon' stored within their sediments; does it stay in the ground, or is it released into the atmosphere? Is it possible to manage seagrass ecosystems so that they sequester more blue carbon? With seagrasses now recognised as globally-significant carbon sinks, the answers to these questions have important consequences for nature-based climate change mitigation and adaptation (i.e. 'biosequestration'). We make the case that microbes fundamentally control the fate of sequestered blue carbon within seagrass, and, therefore, management efforts aimed at bolstering blue carbon opportunities within seagrass ecosystems need to target processes that influence (directly or indirectly) microbial remineralisation of blue carbon. New data will be presented showing that blue carbon occurs in hotspots and changes in the geochemistry of seagrass sediments - such as those caused by disturbance - can create hot moments, whereby organic carbon within sediments undergoes rapid and substantial microbial remineralisation. In order to better manage seagrass ecosystems for blue carbon benefits, we outline three recommendations: reducing anthropogenic nutrient inputs, reinstating top-down control of bioturbator populations, and restoring hydrology. These processes are amenable to management control, they promote microbial dormancy and limit microbial priming, and offer ecosystem benefits beyond carbon sequestration

'A feminine touch’: gender, design and the ocean liner

This article offers an interdisciplinary account of gender in relation to ocean liner interior design. It outlines a case study of what the discipline of design history can bring to gender and maritime history. A historiography of the subject is followed by an analysis of the ways in which the spaces on board British ocean liners were conceived of, designed and used in terms of gender. Some spaces on board were designated as female only and other spaces understood to be male only – particularly the smoking room. The concluding part of the article considers the role of women designers within the patriarchal world of ship design and construction, by investigating the contributions of Elsie Mackay at P & O and the Zinkeisen sisters on the Queen Mary. Using primary sources, including visual evidence, the article considers a range of liners, from the Hindostan (1842) through to the Orontes (1929; refitted 1948). This bridges the gap between design history, gender and maritime history and adds to debates around gender and maritime history with a consideration of the overlooked area of design and its histories

Author Correction: The future of Blue Carbon science.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Operationalizing marketable blue carbon

The global carbon sequestration and avoided emissions potentially achieved via blue carbon is high (∼3% of annual global greenhouse gas emissions); however, it is limited by multidisciplinary and interacting uncertainties spanning the social, governance, financial, and technological dimensions. We compiled a transdisciplinary team of experts to elucidate these challenges and identify a way forward. Key actions to enhance blue carbon as a natural climate solution include improving policy and legal arrangements to ensure equitable sharing of benefits; improving stewardship by incorporating indigenous knowledge and values; clarifying property rights; improving financial approaches and accounting tools to incorporate co-benefits; developing technological solutions for measuring blue carbon sequestration at low cost; and resolving knowledge gaps regarding blue carbon cycles. Implementing these actions and operationalizing blue carbon will achieve measurable changes to atmospheric greenhouse gas concentrations, provide multiple co-benefits, and address national obligations associated with international agreements