Assessing the effectiveness of past mangrove afforestation projects is vital for guiding future initiatives and enhancing success in areas eligible for restoration. This can be assessed by analyzing ecosystem carbon (EC) density, which includes both vegetation carbon (VC) density and soil organic carbon (SOC) density. Using 72 representative plots across five stand ages (12-44 years), we evaluated EC density in Sonneratia apetala-planted mangroves within the planted mangrove reserves in Bangladesh. Results revealed significant differences in VC density, SOC density, and EC density across varying stand ages, soil depths, and mangrove locations. The increased EC density observed over 44 years mangrove reserves (10.06 t/ha/year) with advancing stand ages provides empirical evidence for the effectiveness of afforestation in enhancing EC density levels in mangroves. Notably, the higher SOC density in the upper (0-20cm) soil layer (46 t/ha in 44-year-old stands) compared to the lower (40-60cm) soil layer (21 t/ha in 32-year-old stands) across mangroves indicates that most soil carbon is concentrated in the top 20 cm of the forest floor. The inverse relationship between climate extremes and SOC concentration and SOC density across mangrove reserves suggests that regardless of variations in stand ages and tree density, warming accelerates SOC decomposition and leads to a decline in SOC density. These findings underscore the critical role of afforestation in improving carbon density in mangroves, highlighting the need for continued investment in restoration efforts to maximize their ecosystem services.
How to cite: Hossain, Md. L.: Increasing stand age accelerates ecosystem carbon density while climate extremes reduce soil organic carbon density in 12-44 year-old Sonneratia apetala mangroves in Bangladesh, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1020, https://doi.org/10.5194/egusphere-egu25-1020, 2025.
Mangroves provide habitats for many marine species and support fisheries in developing tropical countries. However, mangrove habitats are increasingly threatened by climate change. Here, we show how global warming and rising atmospheric CO2 will reduce dissolved oxygen and increase CO2 in mangrove waters, making them less suitable as fish refugia. Global observations from 23 mangroves revealed that most sites already experience mild (on average, 34–43% of the time) or severe (6–32%) hypercapnic hypoxia, i.e., low oxygen and high CO2 conditions. Hypercapnic hypoxia mostly occurs during low tide and in tropical mangroves. Climate projections indicate that oxygen will decrease by 5–35% and CO2 will increase by 8–60% by 2100. Therefore, hypercapnic hypoxia events will occur more frequently, last longer, and become more severe. These shifts will reduce mangrove biodiversity and decrease habitat quality for commercially valuable fish, likely reducing fishing yields in tropical developing countries.
How to cite: Reithmaier, G., Pezner, A. K., Ulfsbo, A., Melzner, F., and Santos, I. R.: Climate change amplifies mangrove hypercapnic hypoxia and threatens fish habitats, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2042, https://doi.org/10.5194/egusphere-egu25-2042, 2025.
Mangroves, as a vital component of blue carbon ecosystems play a crucial role in carbon sequestration and climate change mitigation. However, intensified anthropogenic activities such as aquaculture and agricultural farming resulted in significant losses of mangroves worldwide and substantially affected their carbon storage capacity. By developing a 1-km global gridded dataset of mangroves’ accumulated carbon storage from 2000 to 2020, we identified regional hotspots of carbon stock changes at different spatial scales and assessed the impact of mangrove extent changes on carbon sequestration capacity. The outcomes revealed the spatial-temporal heterogeneity of mangrove accumulated carbon storage and could serve as a reference for implementing reforestation initiatives in vulnerable areas, thus supporting the sustainable management of global mangrove ecosystems.
How to cite: Wang, M., Zhang, T., Xie, Y., Zhang, Z., and Wu, X.: Revealing accumulated carbon storage of global mangroves from 2000 to 2020, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4999, https://doi.org/10.5194/egusphere-egu25-4999, 2025.
This study investigates the potential of blue carbon in mitigating climate change in the Mekong Delta, Vietnam, focusing on the interplay between policy, science, and practical implementation. It examines the role of mangroves in carbon sequestration, highlighting their significance in the global carbon cycle and their capacity to mitigate climate change. The research analyzes Vietnam's forest conservation policies, assessing their impacts on blue carbon projects.
Field studies across Ca Mau province in the Mekong Delta quantified mangrove carbon stocks, revealing significant carbon sequestration potential. However, mangrove loss due to land conversion and aquaculture poses a challenge. Policy analysis reveals that while Vietnam has a framework for forest management, including provisions for sustainable use and reforestation, certain regulations, particularly those concerning land use ratios and harvesting practices, can hinder mangrove restoration and blue carbon initiatives.
The study proposes an intervention strategy to enhance blue carbon sequestration, emphasizing sustainable silvicultural practices, sediment management, and the integration of mangrove conservation with aquaculture. Crucially, it advocates for a community-centered approach that protects livelihoods, provides financial compensation for potential income loss due to conservation efforts, and builds capacity for sustainable aquaculture practices. This research underscores the urgent need to align policies with scientific understanding and community needs to effectively harness the climate change mitigation potential of blue carbon in the Mekong Delta.
How to cite: Trinh, H. and Truong, V.: Blue Carbon in Mekong Delta: Linking Policy, Science and Practice, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6820, https://doi.org/10.5194/egusphere-egu25-6820, 2025.
The Mekong Delta is one of the largest deltas in the world, spanning approximately 55,000 km2 and sharing approximately 50.2% of Vietnam’s mangrove ecosystems (90.8 km2 km2; Tinh et al., 2022). Supporting ~18 million people, the Mekong Delta region faces many pressures, including land conversion for shrimp aquaculture, expanding urban centres, deforestation, and coastal erosion. In response to these challenges, mangrove forests in the Mekong Delta have been the focus of several restoration and conservation efforts in recent years, with 27.3 km2 of coastal mangrove forests currently being restored and/or conserved under current forest management efforts.
The purpose of this study is to quantify how mangrove restoration in Ca Mau province, Viet Nam, delivers blue carbon additionality within mangrove ecosystems, particularly where land conversion for shrimp aquaculture has driven deforestation. Field sampling for total ecosystem carbon stocks across natural and restored forests, including integrated shrimp-mangrove aquaculture systems, reflecting one of the region's dominant land-use practices, was carried out by using standardized blue carbon protocols. Mangrove tree diameter, height and species, and downed dead wood were measured and recorded to estimate biomass and necromass carbon stocks. 397 soil samples were collected to estimate belowground soil carbon stocks. Preliminary results from two natural and two restored sites of different ages, show clear evidence of additionality in both aboveground and belowground carbon stores after restoration. However, a comparison of earth observation data between 2010 and 2024 allows us to provide a tentative estimate of carbon losses due to ongoing coastal erosion in these fringing mangrove forests.
These results highlight that efforts to restore mangrove forests in the Mekong Delta can deliver quantifiable blue carbon benefits, potentially underpinning new carbon crediting opportunities to help fund further mangrove restoration across the Mekong Delta. For restoration efforts to be effective in the long-term, careful consideration of ongoing habitat loss, increasingly driven by coastal erosion in response to anthropogenic sea-level rise, will be necessary.
How to cite: Vinh, T. V., Tuan, H. L., Sasmito, S. D., Rovai, A., Wolfe, J. L., Kongsap, V., Masque Barri, P., Linh, T. V. K., Brook, T., Biddulph, G., and Austin, W.: Blue Carbon Additionality and Permanence in the coastal mangrove forests of the Mekong Delta, Viet Nam, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6904, https://doi.org/10.5194/egusphere-egu25-6904, 2025.
Mangrove forests offer a wide range of ecosystem services that benefit both nature and communities living in and around them. Therefore, effective resource management is essential to sustain these invaluable benefits for future generations. Successful mangrove restoration and conservation relies on the foundation of rigorous baseline data. West Africa Blue (“Blue”) is a high-integrity developer of blue carbon projects in West and Central Africa, with two projects (Sierra Leone and Guinea) currently listed in the Verra registry. To ensure we provide the highest level of data possible for our carbon projects, we establish baselines for deforestation, restoration, carbon and biodiversity using rigorous analyses, including GIS-based tools, field data collection, and stakeholder and community engagement. Our system involves methodologies for assessing baseline deforestation and restoration potential, map validation, aboveground biomass, soil organic carbon, and biodiversity baseline. Utilizing public data and field validation exercises, our mapping processes are shown to generate mangrove change results with over 95% accuracy. Using standard operating procedures, we collect AGB data from the field to establish a regional AGB map using SAR and Lidar data. We collected data from Sierra Leone and Guinea and additional AGB data from Nigeria to establish a radar-AGB equation with RMSE of 70 tC/ ha and R2 of 0.41. Leveraging on over 3000 samples of cores, our long-term goals is to establish a regional organic matter (% LOI) ~ organic carbon (% Corg) equation to give a quicker and more accurate estimate of mangrove soil organic carbon.. Further, we carried out a biodiversity baseline assessment in collaboration with a local conservation organization in Sierra Leone called the Conservation Society of Sierra Leone (CSSL) using a mix of innovative and traditional methodologies, including Local Ecological Knowledge (LEK) surveys, camera traps, transects, and environmental DNA (eDNA) analysis with Nature Metrics. Establishing this comprehensive mapping, carbon and biodiversity baseline information helps build a strong foundation for effectively planning mangrove restoration and conservation.
How to cite: Nwobi, E., Reardon, K., Rohan, F., Aslam, A., Mayer, M., Bryan, T., Fitzpatrick, S., and Zaheer, L.: Rigorous Baseline Data: The Key to Successful Mangrove Conservation and Restoration Projects in West Africa., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9117, https://doi.org/10.5194/egusphere-egu25-9117, 2025.
The Intergovernmental Panel on Climate Change (IPCC) currently recognizes vegetated coastal systems, such as saltmarshes, as actionable blue carbon habitats. While not yet officially acknowledged by the IPCC, recent research has highlighted the important role of adjacent mudflat habitats in long-term carbon storage, leading to their growing recognition as “emerging” blue carbon systems. Currently, most research on soil organic carbon (OC) dynamics in the intertidal zone focuses on either saltmarshes or mudflats, while overlooking transitional ecotonal zones. While OC dynamics in saltmarshes have been the main focus of the research community, significantly less attention has been given to tidal mudflats.
We collected soil cores from two different estuaries in England, along transects spanning the pioneer saltmarsh–mudflat ecotone to compare changes in OC storage, accumulation rates, and organic matter (OM) reactivity across these habitats. OC accumulation rates were calculated using 210Pb and 137Cs dating techniques. OM thermal reactivity, reflecting the susceptibility of soil OM to decomposition largely influenced by the balance of labile and recalcitrant OM pools, was assessed using the Carbon Reactivity Index (CRI) via thermogravimetric analysis.
Our results reveal that OC stocks, OC accumulation rates, and CRI values are similar across the pioneer saltmarsh–mudflat ecotone. In comparison to other saltmarsh systems across Great Britain, OC stocks were lower in both the saltmarsh and mudflat zones, yet OC accumulation rates were similar to published saltmarsh data from other regions in the UK. The CRI values indicate that OC stored in pioneer saltmarsh soils are more reactive, and therefore potentially at higher risk of remineralization than adjacent mudflat soils.
Our results suggest pioneer saltmarshes and mudflats, while exhibiting similar OC stocks and OC burial rates, do however exhibit marked changes of OM reactivity. The dynamic nature of these intertidal systems likely increases mineralization of high-reactivity OM across the ecotone, leading to the observation that intertidal mudflats are stores of relatively more stable OM compared to the adjacent pioneer saltmarsh. Our research contributes to the overall understanding of OC storage in saltmarsh pioneer zones and mudflats. We aim to help managers prioritize areas based on both their total OC stocks and their potential for OC remineralization, focusing efforts on protecting high-degradation risk zones.
How to cite: McIntosh, C. L., Smeaton, C., Huston, A., Chalmers, K., Carl, L., Yang, H., and Austin, W. E. N.: Soil organic carbon content and reactivity at the pioneer saltmarsh-mudflat ecotone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9591, https://doi.org/10.5194/egusphere-egu25-9591, 2025.
Saltmarshes, recognized as effective organic carbon (OC) sinks, have gained attention for their potential contribution to climate mitigation through protection and restoration. However, the heterogeneous and geologically young nature of Nordic coastal marshes likely explains the limited research on their climate mitigation potential. To fill this gap, we examined soil OC storage, long-term OC accumulation rates, and soil methane emissions across four Nordic coastal marshes spanning broad climate and environmental gradients. Additionally, we evaluated the effects of grazing, a common management practice. The four Nordic saltmarshes assessed store a median of 7 kg OC m−2 (interquartile range, IQR: 8–6) in the top 15-35 cm of soil and accumulate 41 g OC m−2 yr−1 (IQR: 47–32). Considering only the saltmarsh's additional OC, most relevant to climate mitigation, these values drop to 4 kg OC m−2 (IQR: 6–2) and 21 g OC m−2 yr−1 (IQR: 33–11). Globally, both rates are comparatively low. Higher saltmarsh age and root:shoot ratio strongly and positively correlated with OC stocks and accumulation rates. The elevated root:shoot ratios seemed a morphological adaption to stressful conditions (higher soil salinity, slightly alkaline soils, warmer temperatures, and low water and nutrient availability) reflected in the saltmarsh plant composition. Soil methane emissions reduced the climate benefit of OC accumulation by 0.15–7.3% in Danish saltmarshes, which remained strong CO2eq sinks, but by 70% in Finnish saltmarshes, leaving them as much weaker sinks. Grazing slightly increased soil OC stocks but did not affect OC accumulation rates or methane fluxes. However, greenhouse gas emissions from livestock farming, even at low grazing intensity, largely outweighed saltmarsh climate benefits. A comprehensive Nordic saltmarsh management strategy is needed, extending beyond the current focus on biodiversity to include coastal protection, nutrient retention, and other ecosystem services, including their limited, yet relevant, role in climate mitigation.
How to cite: Leiva Dueñas, C., T. Banta, G., Boström, C., Eller, F., Eklöf, J., Holm Andersen, L., Jensen, K., Lanari, M., Logemann, E., Masquè, P., Ostertag, T., Reisdorff, C., Richard, A., Vehmaa, A., Alm, J., and Krause-Jensen, D.: Low climate benefits of Nordic coastal marshes , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10929, https://doi.org/10.5194/egusphere-egu25-10929, 2025.
In coastal wetland ecosystems, decomposition of plant material is a key process in belowground carbon storage dynamics – the organic matter (OM) that does not break down has the potential to be preserved and contribute to soil/sediment carbon stocks. As such, factors that impact decomposition may also impact the capacity of wetlands to act as natural carbon sinks, particularly in a changing climate. OM decomposition is also an important process for the regeneration of nutrients and the support of ecosystem food webs. However, the paradigm of decomposition as an ecosystem service in its own right is less common in the literature for coastal wetland ecosystems than terrestrial or freshwater aquatic ecosystems.
In this presentation, we will explore the current state of blue carbon cycling in the context of decomposition. Studies on both natural litter and standardise tea litter, i.e. TeaComposition H2O, are showing how elevated temperatures enhance decay and reduce carbon preservation, but that other ecosystem-dependent characteristics like inundation and OM quality also influence the magnitude of this temperature effect. Increasing temperatures can also increase plant productivity, leading to scenarios where carbon decay could be mitigated by plant carbon production. Rising sea levels may also impact belowground OM production and decomposition that could affect soil/sediment strength and structure. Lastly, we will also explore this other side decomposition including if we can define a ‘good amount’ of decomposition that supports soil/sediment and ecosystem functions, while also promoting carbon preservation, particularly in management and restoration scenarios. The hope is to stimulate conversation and research ideas for understanding decomposition ecology for blue carbon and beyond.
How to cite: Trevathan-Tackett, S.: Decomposition in coastal wetlands and what may be beyond carbon preservation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1613, https://doi.org/10.5194/egusphere-egu25-1613, 2025.
The protection and restoration of seagrass meadows are recognised contributions to address the combined biodiversity-, climate- and pollution crises because the meadows are hotspots of biodiversity and soil organic carbon (OC) storage and have experienced major global declines in response to pressures. However, the OC storage capacity and the associated climate change mitigation and carbon crediting potential vary among and within seagrass species. Here we address the potential for carbon crediting in meadows of Zostera marina (eelgrass), the most widely distributed seagrass species, through a review of soil OC stocks, accumulation rates and net organic matter inputs (subtracting the inherent mineral-protected OC). Eelgrass soil OC stocks and accumulation rates display a wide range of values, but especially accumulation rates are typically lower than the average global values for seagrasses. Only 22% of the eelgrass soil samples in this compilation would return positive OC values after subtracting the inherent mineral-protected fraction, and OC stocks under eelgrass meadows were generally not significantly different from stocks of nearby unvegetated soils. These features may partly be due to potentially strong spatial heterogeneity and temporal dynamics of eelgrass meadows, general eelgrass traits as well as export of eelgrass carbon beyond the meadows. We discuss how the findings affect the implementation of effective policies and methodologies that are required for the conservation and restoration policies relating to seagrass meadows.
How to cite: Krause-Jensen, D., Leiva Dueñas, C., and Kennedy, H.: Challenges for carbon crediting in Zostera marina (eelgrass) meadows, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12961, https://doi.org/10.5194/egusphere-egu25-12961, 2025.
Seagrass meadows play a significant role in capturing and storing organic carbon, both from its own primary production and from other adjacent habitats. A high accumulation of organic matter can cause oxygen depletion in the sediment due to aerobic remineralization, leaving space for anaerobic remineralization such as methanogenesis, where methane is produced in the final step. The extent of methane production is likely influenced by the quality of the degrading organic matter. In a long-term microcosm experiment, we studied how organic matter from eight different macrophytes, including seagrass (Zostera marina), reed (Phragmites australis), green macroalgae (Ulva lactuca, Ulva sp.), brown macroalgae (Fucus serratus, Ectocarpales), and red macroalgae (Furcellaria lumbricalis and Polysiphonia spp.), added as a carbon source, affects methane production in anoxic seagrass sediments from the cold-temperate Swedish west coast. Sediment from a unvegetated area with low carbon input was mixed with a small amount of seagrass sediment, functioning as an inoculum of the associated microbial community. The sediment was then placed in glass bottles and each carbon source (dried and homogenized) were added separately to the different bottles and mixed in with the sediment. Seawater was added but leaving enough space for a gas phase. The bottles were kept under anoxic condition with nitrogen flushing and a gas-tight septa. The methane in the gas phase were measured regularly (from twice a week in the beginning to once a month at the end) for nearly two years. The total emission was calculated as the cumulative methane emitted from every measuring point during the experiment. Our preliminary findings revealed that methane emission patterns were highly dependent on the carbon source, with the total cumulative methane emission during the experiment ranging between 0.01 and 47.42 mg, which corresponds to a loss of 0.0009 to 4.5 % of the added organic carbon. The two selected red macroalgae in this study, although of different plants structure (i.e. one filamentous and one more rigid), both generated significantly higher methane emission than all the other carbon sources. Thereby, the origin of carbon source appeared to have a greater influence on methane production than the plant structure. From the selected carbon sources, the treatment with red macroalgae yielded the highest methane levels, while the treatment with green macroalgae yielded the lowest levels. Interestingly, the treatment with organic carbon from Z. marina started to produce methane later than any other treatment and showed relatively low methane emissions (with a cumulative value of 2.70 mg corresponding to 0.26% of the added organic carbon) throughout the study period, highlighting that carbon source composition is crucial for the methane emission levels from seagrass meadow sediments.
How to cite: Forsberg, S., Asplund, M., Gullström, M., Kaliff, H., Legrand, P., Deyanova, D., Dahl, M., and Björk, M.: Species-specific methane production in anoxic seagrass sediments is linked to carbon source quality: a microcosm study, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15655, https://doi.org/10.5194/egusphere-egu25-15655, 2025.
Mangroves, with their remarkable carbon sequestration capacity, are presented with significant opportunities for northward expansion driven by climate change, which may offer a potential restoration strategy for regions in China where Spartina alterniflora has been removed. However, few studies have compared the carbon absorption and accumulation between northward-afforested mangroves of varying stand ages and S. alterniflora. This study investigates carbon exchange dynamics and soil carbon accumulation in Kandelia obovate-dominated wetlands (3, 9, and 20 years old) and S. alterniflora in a subtropical estuary in China, while also collecting data on soil sedimentation rates and surface organic carbon content across the four wetlands. We estimated annual carbon exchange using gross primary production (GPP) models based on light intensity, along with ecosystem respiration (Reco) and methane (CH4eco) models adjusted for temperature, combined with year-round monitoring data. Using a space-for-time substitution approach, we examined the carbon sequestration capacity and accumulation rates across different stand ages of northward mangroves replacing S. alterniflora. Our monitoring findings revealed that although net ecosystem exchange (NEE) increased significantly with stand age, it remained slightly lower than that of S. alterniflora. Both Reco and GPP also increased with stand age, but a higher Reco/GPP ratio could offset CO₂ uptake. It was estimated that the Reco/GPP ratio of S. alterniflora (0.89) exceeded that of mangroves. Therefore, the annual carbon fixation through photosynthesis for the 3 yr, 9 yr, and 20 yr stands were 3.6, 5.8, and 9.9 t C m-² ha-¹, respectively. The mature stands exhibited significantly higher carbon fixation compared to S. alterniflora (-750 g C m-² a-¹), suggesting that although the carbon sequestration capacity of the northward mangroves is lower than that of S. alterniflora in the early stages, the carbon sink potential of the progressively maturing mangroves increases with stand age, ultimately surpassing that of S. alterniflora. Besides, CH4eco emissions in mangroves were negligible, similar to S. alterniflora, and lower than those in natural mangroves, likely due to the absence of aerial roots that mediate CH4eco release. Consequently, the net radiative cooling effect of mangroves increased with age, with the sustained-flux global warming potential metric with 100-year (SGWP100) of 20 yr mangroves being double that of 3 yr mangroves, and it exceeds with 9 yr mangroves and S. alterniflora. This indicates that the warming mitigation potential of mature northward mangroves surpasses that of S. alterniflora. The calculation results show that, although the plant carbon pool of S. alterniflora (5.4 t C ha⁻¹ a⁻¹) is significantly higher than that of the 3 yr (3.2 t C ha-1 a-1), 9 yr (2.4 t C ha-1 a-1), and 20 yr (1.5 t C ha-1 a-1) mangrove stands, it lacks long-term stability. Moreover, the soil carbon accumulation rate in S. alterniflora (1.5 t C ha-1 a-1) was significantly lower than that in the 20 yr mangrove stand (2.6 t C ha-1 a-1). This suggests that replacing S. alterniflora with northward-afforested mangroves is an effective long-term strategy for future coasts to enhance blue carbon sequestration.
How to cite: Liu, T., Yang, H., Li, X., Chen, X., and Yan, Z.: Enhancing Blue Carbon Potential: The Role of Northward Mangroves in Replacing Spartina alterniflora Across Stand Age Dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15798, https://doi.org/10.5194/egusphere-egu25-15798, 2025.
Mudflats and saltmarshes are increasingly recognised as having the potential to sequester and store blue carbon. There is interest in whether Managed Realignment (MR), the breaching of coastal defences to allow (re)inundation of land primarily aims to offset habitat losses, may also have additional benefits including the sequestration and storage of blue carbon. However, sequestration rates are expected to be highly variable because of variations in tidal range, suspended matter concentrations, vegetation assemblages and other environmental factors. In addition, to date there is limited consensus on sampling strategy, including maximum coring depth and spatio-temporal sampling interval. For example, maximum coring depths reported in the literature range from 0.1m to 1.0m. This study aims to critically assess the sampling strategy required to quantify carbon stocks in three spatially adjacent but environmentally distinct settings on the North bank of the macrotidal, hyperconcentrated, Humber Estuary, UK: an agricultural field that is a candidate for managed realignment, a recently breached managed realignment site, and a natural saltmarsh.
Cores were sampled to a depth of up to 3m at 59 locations spaced 250m apart in a 4km-long × 1km-wide area. Material extruded from each distinct horizon was grain-sized using a Malvern Mastersizer 3000 laser-diffraction particle analyser and water content and organic and inorganic carbon fractions were quantified using ThermoGravimetric Analysis (TGA; Leco, TGA701). Both organic and inorganic carbon contents were highly variable in the upper 1m, with differing trends between the natural saltmarsh and MR sites in comparison to the agricultural site: in general, organic carbon content was ~6.5% in the upper 1m and decreased to ~3-4% at a depth of 1.5m and 1.8m in the marshes, whereas organic carbon content was ~4.5% in the upper 0.3m and decreased to ~3% at and below a depth of 0.6m in the agricultural field. Inorganic carbon content was ~2% in the upper 0.3m at all sites, but whilst the marshes exhibited minimal variation with depth (varying between 1.8 and 3.8%), the agricultural field exhibited a decline to 0% between 0.4m and 0.8m, before increasing non-linearly to ~6% at a depth of 2m. However, these general trends mask large inter- and intra-site variability, with organic carbon ranging from 1.8% to 10.3% and inorganic carbon ranging from 0% to 8.6%.
The impact of our new empirical results on carbon sequestration estimates was explored using a 100,000-run Monte Carlo simulation framework in which organic and inorganic carbon contents were randomly selected from best-fit pdfs of data including and excluding cores from below 1m and 1.5m. Our results imply that carbon stocks estimated using cores extruded from only the upper 0.3m may significantly overestimate the total carbon sequestered and stored in saltmarshes and managed realignment sites. Cores to quantify carbon stocks in saltmarshes should extend to a depth of at least 1m and ideally to a depth of 1.5m.
How to cite: Trotman, C., Thomas, R., Forster, R., and Rogerson, M.: Are managed realignment sites net carbon sources or sinks? Insights from the Humber estuary, UK. Natural saltmarsh sites store more carbon at depth than managed realignment sites and agricultural land., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8627, https://doi.org/10.5194/egusphere-egu25-8627, 2025.
The overwhelming dispersion of exotic species Spartina alterniflora threatened the structure and function in native coastal ecosystems. Consequently, native saltmarshes restoration has emerged as a nature-based solution following the removal of invasive species. However, given S. alterniflora as a high carbon sequestration species, it remains uncertain on the impacts of native saltmarshes restoration on coastal blue carbon benefits following its eradication. Here, this study quantified atmospheric carbon uptake and organic carbon storage in restored saltmarsh to assess whether native saltmarsh (Phragmites australis and Bolboschoenoplectus mariqueter) restoration can compensate for the carbon sinks and the climate effects following S. alterniflora eradication. The results showed that removal of S. alterniflora drastically reduced atmospheric carbon uptake, with unrestored bare mudflat turning into carbon sources. After restored native saltmarsh, the atmospheric carbon uptake remained lower than pre-eradication levels of S. alterniflora but provided significant greater carbon sink benefits compared to unrestored bare mudflat. Additionally, the total organic carbon density of soil and vegetation at 50 cm depth in restored native saltmarsh (P. australis and B. mariqueter) exceeded that of unrestored bare mudflat by over 1.4 times, restoring over 70% that observed before eliminating S. alterniflora. Considering the sustained global warming potentials (SGWP) of CH4 over the 100-year timescale, both restored native saltmarsh communities exhibited a net cooling effect for mitigating climate warming, compared to invasive S. alterniflora community and unrestored bare mudflat after S. alterniflora removal. Our findings not only reveal that saltmarsh restoration provides a substantial route to mitigating climate change, but also highlight the trade-off between the carbon losses from eliminating invasive species and the carbon offset achieved through restoring native vegetation in affected ecosystems. This study provides actionable insights for regions confronting analogous challenges with invasive species and restoration scenarios, enabling the development of more comprehensive strategies to ensure effective carbon compensation. Future restoration efforts in invaded ecosystems should prioritize co-benefits such as conserving native ecosystems and enhancing carbon sequestration.
How to cite: Wang, D., Labra, F. A., Yang, H., Hu, Y., Zhao, Z., and Yuan*, L.: Restoration of native saltmarshes enhances carbon sequestration and mitigates warming effects following Spartina alterniflora removal, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9674, https://doi.org/10.5194/egusphere-egu25-9674, 2025.
Coastal wetlands - an important blue carbon ecosystems - are an exceptionally efficient carbon storage sinks on Earth with high carbon sequestration capacity, contributing significantly to combating climate change. Accurate carbon budgeting of coastal marshes requires a complete understanding of different processes/components including the net ecosystem exchange of CO2 with atmosphere, the lateral carbon export lost with tidal draining, and the soil carbon accumulation rate. Yet, most, if not all, current studies present these three components separately, largely due to the knowledge gaps among the diffferent disciplines. Here, for the first time, we bring together measurements of eddy-covaiance flux tower, soil carbon burial data, and lateral carbon export measurements collected in the Xisha marsh - a tidal freshwater wetlands near the first order of Yangtze bifurcation in the Yangtze river delta. Each data set is collected, processed and analyzed in part with disciplinary methodologies. High resolution measurements of time series lateral carbon continuted for one complete hydrological cycle in the system and results show that teh lateral carbon loss with tides contribute up to 20% in this dynamic estuarine blue carbon system. This study highlights the importance of taking the lateral carbon loss into consideration for better closing up the estuarine blue carbon budget.
How to cite: Cao, F.: Closing the Coastal Wetlands Carbon Budget using tower-based measurements, soil carbon accumulation rates and high resolution lateral carbon flux observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11664, https://doi.org/10.5194/egusphere-egu25-11664, 2025.
Seagrass meadows are important blue carbon habitats, due to their high productivity and large sedimentary carbon stocks. However, this can be biased when data from larger species, such as Posidonia oceanica, is extrapolated to global coverage. Carbon budgets of smaller seagrass species, such as Zostera noltei, have been seldom studied, despite these being one of the most common species found on North-West European coasts. In seagrass blue carbon studies, the inclusion of greenhouse gas (GHG) emissions is rare. This study addresses key knowledge gaps by analysing GHG (CO2 and CH4) exchange of the intertidal seagrass Z. noltei, in the southern North Sea, UK, across a full seasonal cycle. GHG exchange of Z. noltei meadows and adjacent non-vegetated mudflats (NVMF) were measured using novel in-situ closed-chambers, and the sedimentary microbial communities (notably, methanotrophs and methanogens) were characterised.
Overall, CO2 fluxes of Z. noltei seagrass were not different to that of NVMFs. Seagrass respiration offsets a large proportion of the plant’s carbon sink capacity, and this was particularly noticeable in spring. When methane emissions were included in the carbon budget, both habitats have net zero carbon emissions. The inclusion of respiration and methane emissions, over multiple seasons, are highly important considerations that are often missed in GHG exchange studies, potentially causing overestimations of seagrass blue carbon, globally. This presentation will also discuss seasonal changes in carbon-cycling microbial communities and how they underpin the measured GHG flux. This pioneering research is of international importance with implications for blue carbon science and natural capital markets.
How to cite: Malcolm-McKay, A., Hicks, N., Whitby, C., Underwood, G., Unsworth, R., and Cameron, T.: Microbial driven greenhouse gas flux of the intertidal seagrass Zostera noltei, across a seasonal cycle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17831, https://doi.org/10.5194/egusphere-egu25-17831, 2025.
Eutrophication and climate change are among the most severe and long-standing environmental problems threatening a large variety of coastal habitats and species in the Baltic Sea and elsewhere. Urgent and adequate management actions are needed to mitigate the combined effects of climate change and anthropogenic activities. The overall purpose of this study is to assess the relative influence of past and future climate and land-use change on organic carbon (OC) and total nitrogen (TN) accumulation in Baltic Sea coastal sediments. Preliminary results from vegetated sediments (two monospecific Zostera marina meadows and one mixed habitat with other rooted vegetation) show higher mean OC accumulation rates (17.5 ± 3.7 g m-2 yr-1)in comparison to adjacent unvegetated sediments (14.2 ± 4.0 g m-2 yr-1) but similar mean TN accumulation (2.1 ± 0.4 and 2.0 ± 0.1 g m-2 yr-1, respectively) during the last century. Based on age-depth models and 14C-dated seagrass remains in the sediment, the colonization of the monospecific Z. marina meadows were dated to approximately 100 and 200 years ago (corresponding to 10 and 15 cm sediment depths). The establishment of the seagrass meadows seems to have led to large changes in sediment biogeochemical properties, including increases in %OC, TN and silt-clay content as well as higher proportion of refractory organic matter (lignin and phenol products) and a decrease in sediment density. A similar change pattern in sediment properties (except for no apparent changes in silt-clay and phenol content) was observed in the mixed Z. marina meadow, while this occurred already 2800 (±200) years ago (seen at about 48 cm sediment depth), which was likely due to the site’s location closer to land and more rapid geomorphological changes following land uplift compared to the monospecific Z. marina meadows. There were increased δ15N values during the last 50 to 100 years, which could be a result of increasing nutrient loads from agricultural activities and land-use change. Further analysis using regional land-use and climate models are being applied to decipher the effect of land-use changes, coastal exploitation, and climate change on OC and TN storage in coastal Baltic Sea vegetation and underlying sediments over centennial to millennial scales. This information can help guide coastal management to mitigate further human-induced impacts on coastal ecosystems.
How to cite: Dahl, M., Andrén, E., Asplund, M. E., Björk, M., Mateo, M. A., Serrano, O., Andrén, T., Braun, S., Ežerinskis, Z., Forsberg, S. C., Garbaras, A., Kaal, J., Kylander, M. E., Linderholm, H. W., Madhavu, V. F., Masqué, P., Šapolaitė, J., Svensson, J. R., Vinogradova, O., and Gullström, M.: Influence of past and future climate and land-use change on carbon and nitrogen accumulation in Baltic Sea seagrass meadows, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15220, https://doi.org/10.5194/egusphere-egu25-15220, 2025.
There is interest in using saltmarsh restoration, and that of other so-call blue carbon ecosystems, as a natural climate solution owing to the ability of these wetlands to sequester and store high amounts of organic carbon in their sediments. Given this, it is important to consider if restored saltmarshes come to function in the same way as natural, established habitats of the same type, and to determine the permanence and origin of the carbon stored in their sediments.
Several existing restored UK saltmarshes have not had their carbon stocks and sequestration rates assessed. Furthermore, the numerous studies of saltmarsh carbon stocks that do exist rarely consider the permanence of the carbon found in the sediment, and only sometimes assess whether the carbon comes from in-situ or external marine or terrestrial sources. This information is needed for carbon crediting schemes – how restoration projects can secure funding to ensure their implementation. To convert the carbon stored in a restored saltmarsh to carbon credits, it is necessary not only to quantify the amount of carbon being stored but also to establish whether it was buried due to the restoration and whether it is stored for a meaningful length of time.
Four restored UK saltmarshes were assessed as a part of this study. Firstly, carbon stock estimates were calculated for these sites that have so-far gone unquantified. This was achieved by developing a novel and inexpensive technique using foraminifera to gain an estimate of how much carbon can be attributed to restoration actions. Secondly, the quality/degradability of organic matter was determined using thermogravimetric analysis. And finally, the sources of organic matter were assessed using stable isotopes. Results show that much of the organic matter present in the sediment of the restored marshes is stable and recalcitrant, suggesting that it originated externally and was washed onto the marsh surface by the tide.
This project will add to our knowledge of UK blue carbon stocks while also implementing techniques that provide information additional to what is usually considered in saltmarsh studies. Developing a better understanding of the functioning of restored saltmarshes will allow judgements to be made about the value of restoration as a means of mitigating climate change.
How to cite: Gore, C., Lehtovirta-Morley, L., Chapman, M., Benson, L., Mueller, P., and Nolte, S.: Blue carbon stocks and sources in four restored UK saltmarshes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-630, https://doi.org/10.5194/egusphere-egu25-630, 2025.
The Wadden Sea comprises the largest tidal flats of the world and extensive intertidal seagrass meadows occur in its northern part. However, their carbon storage potential is largely unknown. Belowground burial of carbon was assessed from different locations in 4 seagrass meadows. All meadows are large (76 – 441 ha), with a similar seagrass cover density (60 – 80 %), species composition (strongly dominated by Zostera noltei) and comparable age (> 90 years). The major difference is the sediment: 3 meadows have established on sandy tidal flats and 1 on mud flats. Sediment cores were taken down to 45 - 65 cm depth and organic matter was measured along vertical profiles. In the sandy sediments, the permanent carbon storage was really low, with an organic carbon content below 0.4 % (average 0.22 – 0.38 %). Input to carbon storage originates mainly from internal biomass production and the dominant species Zostera noltei is relatively small (leaf length about 15 cm) and sheds its leaves in winter, which are carried away by the current. However, in muddy sediment the carbon content was also low but with 1.1 % about 3 times higher. Muddy sediments have a low hydraulic connectivity and the sediment is waterlogged also during air-exposure at low tide. Waterlogged conditions make the sediment more anoxic, generating more reduced conditions which slows down decomposition. Furthermore, muddy sediment particles have a larger surface-to-volume ratio, allowing more organic material to adhere to the particles. Also, the sandy sediments occur in higher energy areas, where resuspension is more common, facilitating export of organic matter and lower burial rates.
How to cite: Dolch, T. and Koop-Jakobsen, K.: The impact of sediment grain size on the carbon storage potential of intertidal seagrass meadows in the northern Wadden Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3671, https://doi.org/10.5194/egusphere-egu25-3671, 2025.
Seagrass meadows are pivotal Blue Carbon habitats that support biodiversity, coastal protection, provide vital ecosystem services while mitigating anthropogenic CO2 emissions through carbon sequestration. Globally, they are increasingly regressing due to the combined effects of climate change and human activities. In this context, restoration initiatives facilitate the reintroduction of seagrass meadows to sites where they were formerly present.
This study focuses on a nature-based restoration initiative in the Caleri lagoon, located in the Po River Delta (Italy) where the dwarf eelgrass Zostera noltei was transplanted to restore a depleted habitat.
A total of 135 sods, with a diameter of approximately 15 cm, were transplanted from the donor site in the Venice lagoon in autumn 2022 and late spring 2023.
On field monitoring of seagrass growth was carried out during August 2023 by means of UAV surveys and in June 2024 by means of ground surveys. The UAV survey was conducted employing a lightweight drone equipped with a high-resolution RGB camera. Visual inspection of the high-resolution orthomosaics, combined with prior knowledge of the transplantation sites, enabled precise mapping and identification of the transplanted seagrass sods. Measured diameters ranged from a minimum of 3 cm (indicative of a decrease in leaf density of the sod) to a maximum of 66 cm (indicative of a growth in leaf cover of more than 4 times). Ground measurements taken in June 2024 provided a rough estimate of the eelgrass meadow extent of 60 m2 with continuous meadow patches with diameters ranging between 1.5 and 3 m.
Additionally, the biota sampling and analysis showed clear positive signs of recovery of the benthic community. The diversity and evenness values of the 115 benthic species showed slightly higher values in the transplant site respect to the control site. A higher frequency of epifaunal predators and herbivores, and of organisms with longer life spans and larger body sizes was observed in the macrobenthic community.
The restoration of Z. noltei in the Caleri lagoon exemplifies successful restoration practices that contribute to the mitigation of anthropogenic impacts, reinforcing the role of coastal vegetated ecosystems as buffers against environmental pressures. In addition, this case study underscores the critical importance of interdisciplinary approaches and continued monitoring to optimize restoration efforts and inform blue carbon policy development. In this context, high-resolution, non-intrusive UAV data collection supports monitoring activities by enabling frequent, repeatable surveys, thereby enhancing efficiency in time-sensitive studies.
How to cite: Strati, V., Mistri, M., Albéri, M., Chiarelli, E., Cozzula, C., Cunsolo, F., Elek, N. I., Hasnain, G., Mantovani, F., Padoan, M., Paletta, M. G., Pezzi, M., Raptis, K. G. C., Sfriso, A. A., Sfriso, A., and Munari, C.: Restoration of seagrass meadows through a nature-based solution in the Caleri Lagoon (Po River Delta, Italy) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4378, https://doi.org/10.5194/egusphere-egu25-4378, 2025.
Understanding the carbon sequestration potential of blue carbon ecosystems is a crucial component for developing nature-based solutions to combat climate change. Alkalinity generation is an often-overlooked carbon sequestration mechanism, especially in seagrass meadows. Here, we quantified alkalinity (TA) and dissolved inorganic carbon (DIC) fluxes at temperate seagrass meadows in Sweden, using 24-hour in-situ chamber incubations during the late part of the productive season in early September. Observed net TA fluxes to the water column of 22 ± 10 mmol m-2 d-1 were 19% lower than DIC fluxes (27 ± 6 mmol m-2 d-1). Both fluxes were largely related to day-night cycles. A sink of TA during the day was counteracted by a 3-times stronger source at night. DIC fluxes displayed a highly variable source, being 3 to 50-times higher at night compared to daytime. TA and DIC fluxes were slightly lower than those reported for seagrasses in warmer climates and for other coastal wetlands, i.e., mangroves and saltmarshes. Nonetheless, alkalinity generation in temperate seagrasses contributes to their carbon sequestration potential and warrants consideration in future investigations.
How to cite: Scott-Askin, S., Santos, I. R., Albert, G., Forsberg, S., Asplund, M. E., Deyanova, D., Ricart, A. M., Gullström, M., Björk, M., and Reithmaier, G. M. S.: Quantifying inorganic carbon fluxes in temperate seagrass meadows, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9623, https://doi.org/10.5194/egusphere-egu25-9623, 2025.
Artificial restoration and conservation of kelp forests are globally implemented as part of ‘blue carbon’ initiatives to achieve carbon neutrality in response to climate change. Ecklonia Cava, a kelp species distributed along the eastern and southern coasts of Korea, plays a significant role as a primary producer in coastal rocky shores. Quantitative analysis of its productivity is essential to evaluate the ecological importance of coastal rocky shores in global carbon sequestration.
We quantified the oxygen flux on daily to seasonal timescales in Ecklonia Cava forests located on the eastern coast of Jejudo Island using the aquatic eddy covariance method. Additional measurements were conducted within the forest using custom-made multiple oxygen optode sensors to investigate oxygen dynamics associated with kelp metabolism. The oxygen flux exhibited daily and seasonal variability, strongly influenced by light availability, tidal flow velocity, temperature, and biomass. Dependent relationships between oxygen flux and environmental parameters, based on a partial least squares regression model, indicate that Ecklonia cava was stressed by dynamic environmental conditions. While substantial gross primary production was observed across seasons, net autotrophic conditions were observed only in spring. Seasonal differences in ecological function were closely associated with increased respiration and biomass loss caused by elevated temperatures during summer and autumn. Additional measurements within the forest revealed diurnal variations in oxygen flux depending on distance above the seabed, reflecting active photosynthetic and respiratory processes of kelp and benthic communities. Moderately tall (50-60 cm) Ecklonia Cava significantly contributes to carbon sequestration and ecological services.
How to cite: Lee, J. S., Lee, C. H., Baek, Y.-J., Kim, S.-H., Kim, K.-T., Choi, D. M., and Kim, T.: Seasonal Dynamic Response of Oxygen Flux in Ecklonia Cava Forests to Environmental Factors: An Aquatic Eddy Covariance Study, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15168, https://doi.org/10.5194/egusphere-egu25-15168, 2025.
The state of Maine has the second largest area of salt marsh habitat in the Northeast US, thus representing a significant coastal carbon sink in the region. Many of these marshes experience restricted tidal inundation which can result in decreased efficiency of carbon sequestration and storage. Little is known about the carbon dynamics associated with tidal restrictions in Maine salt marshes. This study examines carbon dynamics upstream and downstream of tidal restrictions in 3 salt marshes in Maine, USA: the Spurwink Marsh, in Cape Elizabeth; the Drakes Island Marsh, in Wells; and, the Jones Creek Marsh, in Scarborough. In summer of 2023, carbon dynamics were assessed by measuring monthly greenhouse gas fluxes and pore water salinity, and by analyzing the soil core carbon density and longterm carbon sequestration rates. Stream channel water levels and vegetation were also analyzed and provided some insight on the impact of the tidal restriction on the carbon dynamics of each marsh. Each site behaved differently, due, in part, to the degree to which the tidal restriction appears to impact the hydrology of the site. The Spurwink Marsh has excellent hydrologic connectivity upstream and downstream of the restriction with similar soil carbon densities and sequestration in both areas of the marsh. The highest CH4 fluxes are measured along the margins of the marsh where soil salinities are low and Typha species are growing. The Drakes Island Marsh tidal restriction creates an impoundment which prevents adequate drainage during low tide and likely alters the microbial community in the soils. Upstream of the restriction at Drakes Island, soil salinities are lower and CH4 emissions and carbon sequestration rates are higher. The Jones Creek Marsh is the most degraded site we studied, with the highest rates of peat compaction and largest areas of pool habitat upstream of the restriction. Soil carbon density values are lower upstream of the restriction likely due to increased decomposition in waterlogged soils. CH4 fluxes were not significantly different or high on either side of the restriction. These data provide important baseline information for predicting the carbon benefits that can be accrued with salt marsh restoration via tidal restoration.
How to cite: Johnson, B., Enterline, C., Hollander, J., Dickson, K., Sarrazin, A., Puryear, K., and Moore, S.: Carbon dynamics in three tidally restricted salt marshes in Maine, USA, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20359, https://doi.org/10.5194/egusphere-egu25-20359, 2025.
While research in climate mitigation solutions have led to great interest in Blue Carbon Ecosystems (BCEs), such as mangroves, seagrass meadows, and tidal marshes, there has been a growing understanding that other marine environments could be critical to our understanding of BCEs. These “emerging” BCEs, include tidal flats and marine sediments. While receiving less attention than “traditional” BCEs, unvegetated sediments store significant amounts of carbon, globally accounting for an estimated 3,117,000 Mt of organic carbon (OC) within just the top 1 meter of sediment. The potential contributions of emerging BCEs to carbon sequestration are undoubtedly important, but physical disturbances, such as bottom trawling, dredging and climate-change-related weather events such as storms, risk transforming these carbon sinks into carbon sources. Understanding how physical disturbances affect sediment carbon storage and release is paramount to holistic, practical, and successful protection and management of coastal carbon resources.
This study investigated the relative carbon loss from intertidal sediments with simulated physical disturbance to different depths over 9 weeks. Disturbance was applied to 20 intertidal sediment plots in the Tay estuary, Scotland weekly. The depth of disturbances varied across plots, including 2cm (surface), 10cm, 20cm depths, alongside controls (no disturbance) with 4 replicate plots of each. In addition, complete homogenization of sediment to 30cm depth was performed in the lab to simulate a single large mixing event. In-tact cores were extracted from all plots on weeks 2, 5 and 9 to understand cumulative effects. Each core was capped with a custom-built lid attached to an EMG-5 portable gas analyser to measure CO2 flux from the sediment. Each core was then artificially eroded under flow in the laboratory, with the labile and refractory fractions of the particulate carbon quantified from the eroded material. Cores were sliced to generate sediment profiles of different carbon fractions, and to quantify OC:N ratios.
The single large mixing event simulated in week 9 (sediment homogenised to 30cm) resulted in a significantly higher loss of both labile and refractory carbon during erosion, while the loss of labile and refractory carbon was reduced in plots disturbed to 20cm depth compared to controls. CO2 flux data was variable across the weeks and treatments. While less pronounced, the changes in the carbon and nitrogen composition of sediment bed profiles, together with the resuspension of carbon under flow suggest that repeated disturbances may alter the subsequent loss of labile and refractory carbon to the overlying water column after disturbance events. More importantly, the disturbance from a single large mixing event can lead to significant subsequent losses of both labile and refractory carbon from the bed. Further investigations into the flux of dissolved and particulate carbon due to bed disturbance are required to understand the impact of physical disturbance on mudflat carbon dynamics.
How to cite: Carl, L., Austin, W., and Hope, J.: A case study on the relative organic carbon content response to intertidal sediment disturbances , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18749, https://doi.org/10.5194/egusphere-egu25-18749, 2025.
Saltmarshes provide critical ecosystem services, including carbon sequestration, biodiversity, and coastal protection, underscoring the need to understand how quickly and effectively the benefits recover following managed realignment. Realigned saltmarshes often differ from natural systems, even decades after restoration, and are highly influenced by hydrological and sedimentary changes. Accurately measuring carbon sequestration rates in these areas remains a challenge, given variable sediment accumulation, limited methodological approaches, and delays in carbon sink establishment post-restoration.
This study investigates the sediment structure and geochemical characteristics of both managed realigned and natural saltmarshes in the Ribble Estuary, UK. Sediment cores were collected along transects in three areas: Hesketh Out Marsh West (HOMW), realigned after 27 years of agricultural use; Hesketh Out Marsh East (HOME), realigned after 37 years under agriculture; and the adjacent natural Bank Marsh. Non-destructive ITRAX core scanning was employed to analyse sediment structure and geochemical evolution, supplemented by radiometric dating to determine sedimentation rates.
The findings reveal higher sediment densities at the realigned sites (HOMW and HOME), indicative of extended drainage and compaction. In contrast, natural marsh areas displayed enhanced lamination, reflecting regular tidal inundation and storm events. Following embankment breaches greater sediment dynamics were observed at the realigned sites, with elevated Ca/K ratios at HOME indicating the influx of marine sediments, and historical creek modifications contributing to erosion at HOMW. Notably, trace metal analysis revealed a significant reduction in heavy metal contaminants (Zn, Cu, Pb) at the realigned sites, reflecting a decline in historical industrial pollutants The marked decrease in these metals in realigned sites provided a means to estimate sedimentation rates, which ranged from 1.13–1.80 cm yr⁻¹ in HOMW and 0.87–1.50 cm yr⁻¹ in HOME. In contrast, radiometric dating highlighted spatial heterogeneity in sediment deposition across the estuary. Accretion rates at the natural Bank Marsh varied by elevation, from 0.21 cm yr⁻¹ in the upper marsh to 1.02 cm yr⁻¹ in the lower marsh—rates similar to those in the managed realignment sites, particularly HOME. Surprisingly, the more recently realigned HOME did not show higher accretion rates compared to HOMW or Bank Marsh, emphasizing the need for a deeper understanding of saltmarsh development under managed realignment. Overall, our findings demonstrate the value of non-destructive core scanning for assessing sedimentation rates where radiometric dating may be limited. They also highlight the complex, dynamic processes influencing sedimentation and carbon accumulation in saltmarsh ecosystems, emphasizing the need for continued, site-specific investigations into managed realignment outcomes.
How to cite: Muliawan, R. E., Becker, A., Monk, S. A., Warwick, P. E., Reading, D. G., Cundy, A., Amoudry, L., and Evans, C.: Restoration and Sedimentation in Managed Realignment Saltmarshes: A Geochemical Perspective, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20403, https://doi.org/10.5194/egusphere-egu25-20403, 2025.
Macrophyte-dominated benthic meadows play a key role in promoting sedimentation, carbon storage, and nutrient sequestration, especially in enclosed systems like coastal lagoons. However, these shallow ecosystems are highly susceptible to climate change and anthropogenic pressures, including nutrient inputs from agricultural runoff and urban discharges. Seagrasses and seaweed help regulate nutrient availability, reducing the risk of eutrophication by limiting nutrients accessible to opportunistic organisms.
In the Mar Menor coastal lagoon (southeastern Spain), recurrent eutrophication events since 2016 have caused severe ecological disruptions, including mass fish mortality. These events are driven by persistent nutrient inputs resulting from intensified agricultural practices. While the allochthonous seaweed Caulerpa prolifera and the native seagrass Cymodocea nodosa have demonstrated significant nutrient-sinking capabilities, the buffering potential of C. nodosa has diminished due to population declines during these episodes.
This study analyzed twelve sediment cores for total organic carbon (TOC %), δ¹³C, total nitrogen (TN %), and δ¹⁵N, with age estimations based on ²¹⁰Pb dating. Carbon sequestration rates, nutrient stocks, and nutrient origins were determined. Results revealed spatial variability in nutrient distribution, with higher organic carbon enrichment from terrestrial sources concentrated in the lagoon's central areas connected to agricultural lands. Nutrient-depth profiles indicated increased nutrient input beginning in the early 20th century.
The seasonal dynamics and potential loss of macrophyte meadows could exacerbate resuspension events, releasing nutrient-enriched sediments and triggering eutrophication, leading to ecological and socio-economic consequences. Understanding the role of macrophyte meadows in nutrient cycling within sediment-focused, enclosed systems is crucial for effectively managing and conserving these impacted habitats.
How to cite: Alorda-Montiel, I., Arias-Ortiz, A., Rodellas, V., Rodríguez-Puig, J., Alorda-Kleinglass, A., Diego-Feliu, M., Masqué, P., Gilabert, J., and Garcia-Orellana, J.: Macrophyte Meadows in Europe’s Largest Coastal Lagoon: Nutrient and Carbon Sequestration , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19355, https://doi.org/10.5194/egusphere-egu25-19355, 2025.
The distribution of coastal habitats has major implications for biodiversity, population dynamics and various ecosystem services such as protection against erosion, nutrient uptake and blue carbon (BC) storage. Therefore, mapping of habitats in the coastal zone is essential and a prerequisite for understanding their spatiotemporal distribution and configuration. In this study, we compiled existing data based on remote sensing, spatial statistical modelling and ground-truth surveys to map the distribution of established (i.e. saltmarshes and seagrass meadows) and potential BC habitats (including other rooted submerged macrophytes besides seagrass and coastal forested wetlands) along the entire Swedish coastline. The coast was delimited to areas on land with an elevation of 5 meters or less and shallow-water areas down to a depth limit of approximately 6 m. Additionally, as a proxy for the effects of land-based human activities on the mapped BC habitats, a landscape analysis based on the distance to and total area of agricultural and urban areas in Sweden’s coastal drainage basins was carried out. The total area of BC habitats was estimated to be around 1900 km2, corresponding to about 30% of the total delimited Swedish coastal area. Seagrass meadows and shallow-water areas dominated by other rooted submerged macrophytes were the dominating BC habitats, covering approximately 1000 km2 and 500 km2, respectively. Following the natural salinity gradient along the Swedish coastline, seagrass meadows dominated in the marine environment on the Swedish west coast (including the Skagerrak, Kattegat and the Öresund area) and the southern part of the brackish Baltic Proper, while other rooted submerged macrophytes were primarily found at low salinity levels (~5 PSU and lower) in the northern Baltic Proper, Bothnian Sea and Bothnian Bay. The distance- and area-based landscape analysis showed that around 23% of the mapped BC habitats are areas potentially moderately to highly affected by land-based activities. BC habitats inside protected areas were found to be at a significantly lower risk compared to habitats outside protected areas (p < 0.05), but still around 24% (corresponding to an area around 130 km2) of the protected BC habitats are potentially moderately to highly affected by land-based activities. This nationwide mapping of both established and potential BC habitats shows that a large proportion of the long Swedish coastal zone includes BC habitats with great potential for supporting climate change mitigation and adaptation. Furthermore, this study contributes with important baseline information useful for assessing all possible BC habitats along the Swedish coastlines and highlights the importance of coastal management and marine spatial planning for the conservation of these habitats.
How to cite: Braun, S., Dahl, M., Asplund, M. E., Ebert, K., Björk, M., and Gullström, M.: The distribution of potential blue carbon habitats in Sweden, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15958, https://doi.org/10.5194/egusphere-egu25-15958, 2025.
Salt marshes are regarded as key blue carbon stocks with high rates of carbon sequestration due to tidal inundation. However, the impacts that rising sea levels and human development and alterations to salt marshes have on carbon stocks and organic matter deposition have yet to be fully understood. The Sprague River Marsh, in Phippsburg Maine, has been subject to many alterations through the last 400 years (ditching, the building of a tidal restriction and the dredging and redirection of the natural tidal channel). This study analyzes the geochemical records (carbon density and sequestration, d13C, d15N, and C:N ratio) of 40 previously collected sediment cores and 3 new sediment cores, from the Sprague River Marsh. The carbon density data were used to identify areas of high carbon stocks within the upper meter of the marsh. The northernmost area of the Sprague Marsh had significantly higher carbon stocks than elsewhere. The stable isotope data were parsed into different time intervals (0-50, 50-100, 100-200, 200-300, 300-500, 500-1000, 1000-2000 YRS BP) based on an age model derived from 7 radiocarbon dates. Marsh surfaces were mapped using ArcGIS and Empirical Bayesian Kriging to identify areas and times where organic deposition was dominated by high salt marsh, upland plant input, or marine input. These marsh surface reconstructions illuminate shifts in organic matter deposition with changes in relative sea level rise (in agreement with Johnson et al., 2007), the dredging of the tidal channel, marsh evolution and colonization, and growth of the marsh prior to European Colonization. This detailed history of Sprague Marsh can be used to identify areas of high carbon content and the number of sediment cores needed to accurately reconstruct marsh history and analyze and predict carbon stocks.
How to cite: Welch, A., Johnson, B., Dostie, P., Danahey, M., Kolff, A., Larson, I., Marchand, E., Baker, R., Blodgett, H., and Turtle, S.: High Resolution Mapping of Carbon Stocks and Sequestration and Organic Matter Sources over the last 2000 Years in the Sprague River Marsh, Phippsburg Maine, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14310, https://doi.org/10.5194/egusphere-egu25-14310, 2025.
Climate change-induced sea-level rise and saltwater intrusion are expected to significantly influence carbon cycling in estuarine marshes by affecting microbial litter decomposition. However, the extent and mechanisms of these changes remain unclear. In this study, we investigated the impacts of litter quality and environmental conditions on litter decomposition and prokaryotic communities in an estuarine environment. We incubated both native and standardized litter (Tea Bag Index) in soils representative of various marsh types (freshwater, brackish, and salt) and different flooding frequencies (daily, monthly, and yearly) along the Elbe Estuary. The prokaryotic communities colonizing the litter and soil were characterized through 16S rRNA gene amplicon sequencing. Our findings indicate that litter quality plays a crucial role in litter decomposition along estuarine gradients. The decomposition of native litter increased with higher salinity and reduced flooding frequency, primarily influenced by the chemical properties of the litter, particularly lignin content and the lignin:N ratio. Conversely, the decomposition of tea litter decreased as salinity increased, suggesting that rising salinity creates unfavorable conditions for decomposition. The effects of flooding varied depending on litter quality: mass loss of recalcitrant litter (rooibos tea) diminished with more frequent flooding, while mass loss of labile litter (green tea) increased. Prokaryotic communities in both native and tea litter exhibited distinct assemblages and lower diversity compared to the local soil community, indicating selective colonization of the litter, which was especially evident for tea litter. Furthermore, tea mass loss was enhanced by a diverse soil prokaryotic community, whereas the decomposition of native litter seemed to be driven by an adapted soil prokaryotic community. Our results underscore the influence of biotic factors (litter quality and prokaryotic communities) and abiotic factors (salinity and flooding) on litter decomposition in estuarine ecosystems, suggesting that anticipated changes in salinity and hydrodynamics due to climate change could substantially alter decomposition dynamics in these environments.
How to cite: Neiske, F., Grüterich, L., Eschenbach, A., Wilson, M., Streit, W. R., Jensen, K., and Becker, J. N.: Litter Quality Drives Decomposition and Prokaryotic Communities in Estuarine Marsh Soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16693, https://doi.org/10.5194/egusphere-egu25-16693, 2025.
Posters virtual: Wed, 30 Apr, 14:00–15:45 | vPoster spot A
EGU25-1419 | ECS | Posters virtual | VPS4
Mangroves and their services are at risk from climate-modified tropical cyclones and sea level riseWed, 30 Apr, 14:00–15:45 (CEST) | vPA.18
Climate change is expected to alter the frequency and intensity of extreme events, modifying the natural disturbance regimes to which ecosystems are currently adapted. Here, we present a spatially explicit risk index for mangroves and their associated biodiversity and ecosystem services based on projected frequency changes of tropical cyclone wind speeds and rates of relative sea level rise under SSPs 245, 370 and 585 by 2100.
To compute the risk index, we calculate the relative change of tropical cyclone frequency across different wind speed intensity categories based on probabilistic tropical cyclone tracks downscaled from 3 different CMIP6 models of varying climate sensitivity. This data is then combined with thresholds of sea level rise which are estimated to exceed mangrove adaptive capacity and mapped onto global mangrove extents.
Globally, approximately half of the total mangrove area (40-56% depending on the SSP) will be at high to severe levels of risk due to climate-modified tropical cyclone disturbance regimes. Further, we find mangrove areas with high levels of biodiversity and ecosystem services provision, including coastal protection for people and assets, carbon sequestration, and fishery benefits, are at proportionally higher levels of risk than mangrove forests generally. We also identify mangrove areas which are projected to experience non-analog tropical cyclone disturbances in the future. Our findings emphasize the need to anticipate changes in natural disturbance regimes to adapt ecosystem management, sustain ecosystem services in the future, and fully realize mangroves’ potential as nature-based solutions (NBS).
How to cite: Hülsen, S., Dee, L., Kropf, C., Meiler, S., and Bresch, D.: Mangroves and their services are at risk from climate-modified tropical cyclones and sea level rise , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1419, https://doi.org/10.5194/egusphere-egu25-1419, 2025.
EGU25-7982 | ECS | Posters virtual | VPS4
Estimating the Potential Greenhouse Gas Emission from Degraded Seagrass Meadows: A Case Study from Thailand's Seagrass EcosystemsWed, 30 Apr, 14:00–15:45 (CEST) | vPA.19
The seagrass meadows are critical for organic carbon storage and play a significant role in mitigating climate change. However, the ongoing degradation of the seagrass meadows in Thailand reduces their ability to sequester carbon effectively, potentially contributing to greenhouse gas (GHG) emissions. This study examines variations in carbon storage, carbon metabolism, and GHG emissions across degraded, healthy seagrass and bare sand areas along Andaman Sea, Thailand. The average carbon storage within the surface sediment (top 10 cm) varies across seagrass conditions, with the highest carbon storage in heavy degraded (365.2 ± 206 g C m-2), followed by bare sand (289.5 ± 236 g C m-2) and healthy seagrass (86.47 ± 5.8 g C m-2). Furthermore, degraded seagrass and bare sand exhibited heterotrophic ecosystem functions with an average NCP value of 0.44 ± 0.49 and -0.13 ± 0.79 mmol C m⁻² d⁻¹, respectively. Conversely, healthy seagrass maintained autotrophic ecosystem functions with NCP 1.30 ± 0.508 mmol C m⁻² d⁻¹. The average total carbon sink varied among seagrass conditions, with the highest in degraded seagrass (4328 ± 2395 CO₂-eq m⁻² d⁻¹), compared to bare sand (3981 ± 4120 CO₂-eq m⁻² d⁻¹) and healthy seagrass (1630 ± 0 CO₂-eq m⁻² d⁻¹). The study also revealed that CH4 emissions dominated GHG fluxes in all seagrass conditions, with the highest mean CH₄ fluxes recorded in degraded seagrass (1.16 ± 0.51 µmol m⁻² h⁻¹), followed by bare sand (1.02 ± 0.41 µmol m⁻² h⁻¹) and healthy seagrass (0.48 ± 0.07 µmol m⁻² h⁻¹). On the other hand, the CO2 emissions remained consistently low in both seagrass meadows (healthy and degraded) and bare sand areas. These findings are important to indicate and provide the baseline of GHG emissions for healthy and degraded tropical seagrass meadows.
Keywords: Blue carbon, Climate Change, Emission, Greenhouse gas, Seagrass meadows
How to cite: Halim, M., Stankovic, M., and Prathep, A.: Estimating the Potential Greenhouse Gas Emission from Degraded Seagrass Meadows: A Case Study from Thailand's Seagrass Ecosystems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7982, https://doi.org/10.5194/egusphere-egu25-7982, 2025.
EGU25-14608 | ECS | Posters virtual | VPS4
Lack of blue carbon recovery in restored tropical seagrass ecosystemsWed, 30 Apr, 14:00–15:45 (CEST) | vPA.20
Seagrass ecosystems are vital for coastal resilience, biodiversity, and as critical carbon sinks. With global seagrass declines, restoration has emerged as a key strategy for ecological and carbon recovery. Although through seagrass restoration, various ecosystem services return, there is a lack of information on the return of the carbon sequestration and accumulation. This study aims to assess the potential recovery of blue carbon benefits through seagrass restoration across various sites in Thailand. We analyzed carbon stocks and accumulation rates in restored Enhalus acoroides meadows at four sites, evaluating spatial variability in carbon recovery in restored versus natural meadows and unvegetated sediment. Despite successful seagrass establishment, the organic carbon (OC) content (%) within the surface sediment (top 20 cm) was not significantly different among restored, natural seagrass meadows, and bare sand, averaging 0.8 ± 0.1%, 0.9 ± 0.2%, and 0.9 ± 0.2% respectively. Although significant differences in OC content (%) were observed between sites, no differences were noted between the habitat types within each site. Predominantly sandy sediment (over 90%) with minimal mud content (1% or less) were found at all sites. The highest organic carbon stock in surface sediment was in unvegetated sediment, averaging 16.8 ± 3.4 Mg C ha-1. Significant differences in OC stocks were also observed across all site comparisons, with higher stocks generally found in bare sand compared to restored and natural seagrass meadows. Sediment accumulation profiles, indicated by the absence of excess 210Pb, suggest a lack of net fine sediment accumulation over the past decade or mixing of the upper sediment, precluding reliable sedimentation rate estimation. These findings suggest that these restored meadows are not forming depositional environments contributing to significant additional carbon sequestration, as evidenced by the minimal increase in OC stocks across the sites. Additionally, the low OC content (%) and minimal mud presence suggest overall low sedimentation rates, even in natural seagrass meadows. These results highlight the complexity of achieving carbon sequestration goals through seagrass restoration, emphasizing the need for site-specific restoration strategies that consider local sediment dynamics and ecological conditions to enhance carbon storage capabilities.
Keywords: organic carbon, carbon additionality, carbon accumulation, seagrass, restoration
How to cite: Stankovic, M., Kaewsrikhaw, R., Masqué, P., Vanderklift, M. A., Upanoi, T., and Prathep, A.: Lack of blue carbon recovery in restored tropical seagrass ecosystems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14608, https://doi.org/10.5194/egusphere-egu25-14608, 2025.
EGU25-14443 | Posters virtual | VPS4
Study on the Impact of Blue Carbon Ecosystem Protection on the Livelihoods of Coastal Communities in Hainan ProvinceWed, 30 Apr, 14:00–15:45 (CEST) | vPA.21
Blue carbon ecosystems (mangroves, seagrass beds, and salt marshes) are one of the most effective carbon sinks on Earth and are critical to climate change mitigation and adaptation. Hainan Province in China accounts for 82% of the country's mangrove area and 64% of the country's seagrass bed area. Hainan's blue carbon plays an important role in local and national carbon sink enhancement efforts. From the perspective of economics, Hainan's blue carbon system plays a major supporting role in the local economy. Existing research on the protection of China's blue carbon ecosystems focuses on carbon sink accounting and economic valuation, and rarely involves microeconomic impact analysis of blue carbon protection actions. In particular, there are few studies specifically conducted on the impact on residents' livelihoods and well-being in Hainan.
In this context, we are attempting to conduct research in Hainan Province to answer the following questions: What impact does the protection and restoration of Hainan's blue carbon ecosystem have on the livelihoods of its coastal communities? We refined this question into three points: First, what are the livelihood sources and livelihood structures of Hainan's coastal and non-coastal communities; what changes have occurred around 2020? Second, has Hainan's special action on the protection and restoration of blue carbon ecosystems had an impact on the livelihoods of coastal communities? Third, through what channels does Hainan's special action on the protection and restoration of blue carbon ecosystems affect the livelihoods of coastal communities?
According to preliminary research, Hainan Province's special action for the protection and restoration of blue carbon ecosystems has a two-way impact on the livelihoods of coastal communities. On the one hand, blue carbon protection can maintain and promote the local fishery economy and tourism; on the other hand, due to restrictive regulations on the relevant use of marine resources at the policy level, the protection and restoration of mangroves may have a negative impact on fisheries. Maintaining a balance between fishermen's livelihoods and blue carbon protection may be one of the difficulties in blue carbon conservation. Treating the special action for the protection and restoration of blue carbon ecosystems as a quasi-natural experiment, we are going to conduct policy evaluation in our study. We will conduct a community questionnaire survey and introduce the propensity matching difference-in-difference (PSM-DID) model to reveal the net effect of Hainan's blue carbon ecosystem protection on the livelihoods of coastal communities.
How to cite: Chen, Y.: Study on the Impact of Blue Carbon Ecosystem Protection on the Livelihoods of Coastal Communities in Hainan Province, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14443, https://doi.org/10.5194/egusphere-egu25-14443, 2025.
