Blue Carbon Ecosystems Research Articles

Valuing the contribution of blue carbon to small island developing states' climate change commitments and Covid-19 recovery

Small Island Developing States (SIDS) face complex socio-economic and environmental threats, making them particularly vulnerable to climate change. Blue Carbon (BC) ecosystems (mangrove forests, tidal marshes, and seagrass meadows) provide climate regulation services by sequestering and storing carbon, presenting an opportunity for SIDS to address climate change and implement Paris Agreement commitments in their Covid-19 recovery. BC habitat decline not only reduces carbon sequestration benefits provided, but can also result in sediment disturbance and the release of previously stored carbon back into the atmosphere. In this work, a scenario analysis informed by a stakeholder workshop and scientific and socio-economic expectations is used to assess the economic importance of Grenada’s BC (mangroves and seagrasses) over the next 10, 25 and 50 years. Our findings indicate that sequestration benefits are severely diminished under Business-as-Usual habitat loss, but still marginally outweigh losses from carbon emissions, with overall welfare gains of US$0.5–1.9 million over 50 years. To stimulate economic recovery post-pandemic, stakeholders anticipated a realistic scenario of increased habitat decline resulting in overall losses of US$5.4–19.4 million in the next 50 years. However, if ecosystems are maintained, overall carbon benefits could reach US$10.7 million, while a 20% increase in mangroves over the next 25 years provides benefits reaching US$11.1 million between 2020 and 2070. These results demonstrate a significant increase in value when BC ecosystems are maintained and not disturbed, preventing the release of previously stored carbon and enhancing sequestration capacity. Restoration benefits are marginal, compared to conservation, supporting claims that conservation is more cost effective.

Diverse methylotrophic methanogenic archaea cause high methane emissions from seagrass meadows

Marine coastlines colonized by seagrasses are a net source of methane to the atmosphere. However, methane emissions from these environments are still poorly constrained, and the underlying processes and responsible microorganisms remain largely unknown. Here, we investigated methane turnover in seagrass meadows of Posidonia oceanica in the Mediterranean Sea. The underlying sediments exhibited median net fluxes of methane into the water column of ca. 106 µmol CH4 ⋅ m-2 ⋅ d-1 Our data show that this methane production was sustained by methylated compounds produced by the plant, rather than by fermentation of buried organic carbon. Interestingly, methane production was maintained long after the living plant died off, likely due to the persistence of methylated compounds, such as choline, betaines, and dimethylsulfoniopropionate, in detached plant leaves and rhizomes. We recovered multiple mcrA gene sequences, encoding for methyl-coenzyme M reductase (Mcr), the key methanogenic enzyme, from the seagrass sediments. Most retrieved mcrA gene sequences were affiliated with a clade of divergent Mcr and belonged to the uncultured Candidatus Helarchaeota of the Asgard superphylum, suggesting a possible involvement of these divergent Mcr in methane metabolism. Taken together, our findings identify the mechanisms controlling methane emissions from these important blue carbon ecosystems.

Implementation of blue carbon offset crediting for seagrass meadows, macroalgal beds, and macroalgae farming in Japan

The “blue carbon” concept and the role of blue carbon stored in shallow coastal ecosystems in mitigating climate change have attracted attention worldwide. In addition to typical blue carbon ecosystems, such as mangroves, tidal marshes, and seagrass meadows, macroalgal beds and macroalgae farming are also gaining recognition as potential blue carbon sinks. Effective policies and methodologies are important for the conservation and expansion of blue carbon sinks, as well as the consequent reduction of atmospheric carbon dioxide (CO2). One of the most effective methods is carbon offset credit schemes. However, to date, almost all credit schemes have been implemented for mangroves and saltmarshes. None has been implemented for seagrass meadows, macroalgal beds, and macroalgae farming, although their CO2 uptake potentials are large. Here, we review three blue carbon offset credit projects for seagrass meadows, macroalgal beds, and macroalgae farming implemented in Japan. We show the blue carbon offset crediting projects of (1) Yokohama City, the first in the world; (2) Fukuoka City, the second such project in Japan; and (3) the first Japanese national governmental demonstration project. Furthermore, we highlight their characteristics by comparing them with the other blue carbon offset projects. Finally, we discuss the need to accelerate blue carbon offset credit projects and related initiatives in the future.

Plant litter composition and stable isotope signatures vary during decomposition in blue carbon ecosystems

The ratio of isotopes of carbon (13C:12C or δ13C) and nitrogen (15N:14N or δ15N) are common indicators of the flow and storage of organic matter in coastal wetland research. Effective use of these indicators requires quantification and understanding of: (1) the variability of isotope signatures of potential organic matter source materials; and (2) the influence of organic matter decomposition on isotopic signatures. While it is well-established that organic matter characteristics change during the decomposition process, there has been little direct quantification of any concurrent shifts in isotope signatures for coastal detritus. In this study, we addressed this by quantifying: (1) shifts in sample composition using solid-state 13C Nuclear Magnetic Resonance (NMR) spectroscopy; and (2) shifts in δ13C and δ15N signatures of coastal plant tissues from field litterbag experiments. We observed significant shifts in 13C NMR spectra across the course of deployment for all four plant tissues assessed (leaves of mangrove Avicennia marina; branchlets of supratidal tree Casuarina glauca; leaf wrack and roots/rhizomes of the seagrass Zostera muelleri), driven largely by the preferential loss of labile constituents and concentration of more resistant macromolecules, such as lignin and leaf waxes. While there were shifts in isotope ratios for all species, these varied in direction and magnitude among species, tissue type and isotopes. This included δ13C enrichments of up to 3.1‰ and 2.4‰ in leaves of A. marina, and branchlets of C. glauca, respectively, but δ13C depletions of up to 4.0‰ for Z. muelleri. Shifts in δ15N varied among species and tissue types, with few clear temporal patterns. Partial least squares regression analyses showed that some tissue isotope signatures can be reliably predicted on the basis of sample composition (13C NMR spectra), however, multiple inter- and intra-species variations preclude a simple explanation of isotopic signature shifts on the basis of plant-material molecular shifts alone. Further, we cannot preclude the potential influence of microbe-associated organic matter on sample composition or isotopic signatures. Our findings emphasise the importance of considering decomposition effects on stable isotope signatures in blue carbon ecosystems. Isotope approaches will remain a valuable tool in coastal ecosystem research, but require robust experimental approaches (including appropriate use of decomposed end-members or fractionation correction factors; quantification of microbial organic matter) and quantification of decomposition dynamics for specific plant tissues and environmental settings.

Network analysis of blue carbon governance process in Indonesia

To align with international climate efforts to remain within 1.5 degrees of the earth temperature, Indonesia requires concerted measures from actors to preserve and restore carbon rich ecosystems, especially blue carbon ecosystem. Although studies have suggested the importance of blue carbon ecosystems in contributing to Indonesian climate action, translating science to policy remains a challenge. Mapping actors and the pattern of information exchange related to blue carbon can help identify potential barriers in the blue carbon governance process and policy development. This study uses Social Network Analysis and integrates it with results from in-depth qualitative evaluation of institutional respondents. Data is obtained through questionnaires and semi-structured interviews with representatives from a broad range of organizations. It was found that the actor who oversees the fulfilment of the climate commitment, which is the most common objective of the network, is not a central actor. Second, the actors with the highest degree of centrality received little trust from other actors. Third, overall, the network has low quality ties. Each of these hinders knowledge providers’ ability to make an impact on policy development. By critically examining the interactions between actors, this research casts new light on the overlooked problem of the significance of the network in blue carbon governance process.

Beach Wrack Dynamics Using a Camera Trap as the Real-Time Monitoring Tool

As part of Blue Carbon ecosystems (BCEs), detached macrophytes can be transported to the coast due to current and wave actions, and then deposited on the shore as beach wrack. To date, the role of beach wrack in the material cycle in BCEs is still unclear. In order to track the fate of beach wrack, this study conducted a monitoring survey on a semi-sheltered beach in Odense Fjord (Denmark) using camera trap data. Deep learning with a VGG network architecture was used to classify the image dataset acquired by the camera trap. The VGG network demonstrated the capability to identify beach wrack from different beach scenes, and the method can provide results on large datasets within a short time (187 images analyzed within 5 min) compared to manual identification of images. By combining the VGG detection with color-based segmentation, beach wrack coverage was determined. To evaluate the impact of ambient conditions on wrack deposition on the shore and relocation back to the sea, wind (including speed and direction), water temperature, and tidal amplitude were analyzed as environmental variables. Partial least squares regression (PLSR) analysis revealed that micro-tidal action with an average amplitude of 0.41 m accelerated the movement of floating macrophytes between the shore and the sea. Despite being exposed to the prevailing southwesterly winds (average speed of 11 m/s), the beach was sheltered due to the location in the inner part of Odense Fjord, limiting the transport of drifting macrophytes from sea to the shore. By using the camera trap to conduct continuous monitoring, this study presents a labor-saving and practical approach to track the dynamics of detached macrophytes deposited on the shore. Furthermore, the application of deep learning in image identification provides a study case for using a large image dataset to assist in ecological studies of dynamic environments.

Annual Lateral Organic Carbon Exchange Between Salt Marsh and Adjacent Water: A Case Study of East Headland Marshes at the Yangtze Estuary

Blue carbon (C) ecosystems (mangroves, salt marshes, and seagrass beds) sequester high amounts of C, which can be respired back into the atmosphere, buried for long periods, or exported to adjacent ecosystems by tides. The lateral exchange of C between a salt marsh and adjacent water is a key factor that determines whether a salt marsh is a C source (i.e., outwelling) or sink in an estuary. We measured salinity, particulate organic carbon (POC), and dissolved organic carbon (DOC) seasonally over eight tidal cycles in a tidal creek at the Chongming Dongtan wetland from July 2017 to April 2018 to determine whether the marsh was a source or sink for estuarine C. POC and DOC fluxes were significantly correlated in the four seasons driven by water fluxes, but the concentration of DOC and POC were positively correlated only in autumn and winter. DOC and POC concentrations were the highest in autumn (3.54 mg/L and 4.19 mg/L, respectively) and the lowest in winter and spring (1.87 mg/L and 1.51 mg/L, respectively). The tidal creek system in different seasons showed organic carbon (OC) export, and the organic carbon fluxes during tidal cycles ranged from –12.65 to 4.04 g C/m2. The intensity showed significant seasonal differences, with the highest in summer, the second in autumn, and the lowest in spring. In different seasons, organic carbon fluxes during spring tides were significantly higher than that during neap tides. Due to the tidal asymmetry of the Yangtze River estuary and the relatively young stage, the salt marshes in the study area acted as a strong lateral carbon source.

Blue carbon drawdown by restored mangrove forests improves with age

The restoration of blue carbon ecosystems, such as mangrove forests, is increasingly used as a management tool to mitigate climate change by removing and sequestering atmospheric carbon in the ground. However, estimates of carbon-offset potential are currently based on data from natural mangrove forests, potentially leading to overestimating the carbon-offset potential from restored mangroves. Here, in the first study of its kind, we utilise 210Pb sediment age-dating techniques and greenhouse gas flux measures to estimate blue carbon additionality in restored mangrove forests, ranging from 13 to 35 years old. As expected, mangrove age had a significant effect on carbon additionality and carbon accretion rate, with the older mangrove stands (17 and 35 years old) holding double the total carbon stocks (aboveground + soil stocks; ∼115 tonnes C ha−1) and double the soil sequestration rates (∼3 tonnes C ha−1 yr−1) than the youngest mangrove stand (13 years old). Although soil carbon stocks increased with mangrove age, the aboveground plant stocks were highest in the 17-year-old stand. Mangrove age also had a significant effect on soil carbon fluxes, with the older mangroves (≥17 years) releasing one-fourth of the CH4 emissions, but double the CO2 flux compared to young stands. Our study suggests that the carbon sink capacity of restored mangrove forests increases with age, but stabilises once they mature (e.g., >17 years). This means that by using carbon sequestration and emissions from natural forests, mangrove restoration projects may be overestimating their carbon sequestration potential.

Assessing the Effect of Age and Geomorphic Setting on Organic Carbon Accumulation in High-Latitude Human-Planted Mangroves

Mangroves are highly productive blue carbon ecosystems that preserve high organic carbon concentrations in soils. In this study, particle size, bulk elemental composition and stable carbon isotope were determined for the sediment cores collected from the landward and seaward sides of two mangrove forests of different ages (M1, ca. 60; M2, ca. 4 years old) to determine the effects of geomorphic setting and age (L1 = old mangrove and S1 = salt marsh stand in M1; L2 = young mangrove and S2 = bare mudflat in M2) on sediments and organic carbon accumulation. The objective of this study was to determine the feasibility of the northernmost human-planted mangroves in China to accumulate sediment and carbon. Our results showed that fine-grained materials were preserved well in the interior part of the mangroves, and the capacity to capture fine-grained materials increased as the forest aged. The biogeochemical properties (C/N: 5.9 to 10.8; δ13C: −21.60‰ to −26.07‰) indicated that the local organic carbon pool was composed of a mixture of autochthonous and allochthonous sources. Moreover, the accumulation of organic carbon increased with the forest age. The interior part of the old mangrove had the highest organic carbon stock (81.93 Mg Corg ha−1). These findings revealed that mangrove reforestation had positive effects on sediments and organic carbon accretion.

Carbon sequestration is not inhibited by livestock grazing in Danish salt marshes

AbstractClimate change has created a need for solutions that can counteract greenhouse gas emissions. One is the expansion and maintenance of natural carbon (C)‐sequestration habitats, such as forests and coastal and marine vegetated ecosystems, socalled “blue carbon ecosystems” including salt marshes, which represent large and long‐term C‐storage potential. While salt marsh blue carbon is gaining international attention, Baltic and Nordic salt marshes have been neglected in the blue carbon context. Here, we quantified C‐stocks and C‐sequestration rates in grazed and nongrazed sites of three Danish salt marshes, and evaluated whether grazing livestock, the standard management to increase biodiversity of the marshes, affect C‐stocks and sequestration rates. The aboveground biomass and vegetation height in nongrazed salt marshes were significantly larger than for grazed salt marshes, but this did not lead to significantly enhanced overall sediment‐ or C‐accumulation rates. Detailed model analyses of sediment profiles even indicated significantly higher C‐densities in surface layers at grazed sites. Averaged C‐densities, C‐stocks (top 43 cm sediment) and sequestration rates estimated from 210Pb profiles ranged 0.011–0.022 g C cm−3, 4228–8178 g C m−2, and 17–45 g C m−2 yr−1, respectively, with the latter being low in the global context. While this pioneering study for the Baltic and Nordic regions showed a neutral to positive effect of grazing on C‐sequestration, there is a need to explore the overall C‐footprint of this practice, including effects on net greenhouse gas emissions and coastal defense capacity, and define blue carbon management strategies for salt marshes to maximize their climate change mitigation and adaptation capacity while supporting biodiversity.

Mangrove Above-Ground Biomass and Carbon Stock in the Karimunjawa-Kemujan Islands Estimated from Unmanned Aerial Vehicle-Imagery

Blue carbon ecosystems in the Karimunjawa Islands may play a vital role in absorbing and storing the releasing carbon from the Java Sea. The present study investigated mangrove above-ground biomass (AGB) and carbon stock in the Karimunjawa-Kemujan Islands, the largest mangrove area in the Karimunjawa Islands. Taking the aerial photos from an Unmanned Aerial Vehicle combined with Global Navigation Satellite System (GNSS) measurements, we generated Digital Surface Model (DSM) and Digital Terrain Model (DTM) with high accuracy. We calculated mangrove canopy height by subtracting DSM from DTM and then converted it into Lorey’s height. The highest mangrove canopy is located along the coastline facing the sea, ranging from 8 m to 15 m. Stunted mangroves 1 m to 8 m in height are detected mainly in the inner areas. AGBs were calculated using an allometric equation destined for the Southeast and East Asia region. Above-ground carbon biomass is half of AGB. The AGB and carbon biomass of mangroves in the Karimunjawa-Kemujan Islands range from 8 Mg/ha to 328 Mg/ha, and from 4 MgC/ha to 164 MgC/ha, respectively. With a total area of 238.98 ha, the potential above-ground carbon stored in the study area is estimated as 16,555.46 Mg.

Carbon and Nitrogen Contents Driven by Organic Matter Source within Pichavaram Wetland Sediments

Differences in grain size, total organic carbon (OC), total nitrogen (TN), OC/TN ratios, and stable isotope (δ13C and δ15N) were assessed in sediments from areas covered by mangrove and saltmarsh vegetation within Pichavaram estuary (Southeast India). The mean percentage contents of silt and clays (70 vs. 19%), OC (5.7 vs. 2.0%), and TN (0.39 vs. 0.14%) were consistently higher in the mangrove as compared to those observed in the saltmarsh tidal zone. These differences may obey the higher deposition and retention of fine particles in the presence of a mangrove root system that may facilitate the accumulation and preservation of organic matter within these sedimentary systems. Further, higher OC and TN contents were associated to higher terrestrial or mangrove-derived organic matter contribution with lighter δ13C signatures (−26.0‰) in both sedimentary tidal zones, whereas lower OC and TN contents were associated to heavier δ13C signatures. This study is in agreement with previous studies which indicate that the presence of wetland vegetation may increase the carbon and nutrient storage capacity within estuarine ecosystems, highly relevant information for the establishment of further conservation strategies for blue carbon ecosystems at global scales.

First assessment of the blue carbon storage of Rhizophora and Bruguiera mangrove stands on the island of Mauritius (western Indian Ocean)

Blue carbon has gained recognition as a strategy to mitigate climate change. Mangroves allow significant amounts of carbon to be sequestered and stored and are considered an important component in the offset of greenhouse gas emissions. Despite this, little is known about the ecosystem-level carbon storage of the mangrove stands of Mauritius, western Indian Ocean. We conducted an inventory of mangrove stands to characterise forest stand structure and estimate carbon stocks in terms of aboveground biomass and soil carbon at two sites, Ferney and Pointe d’Esny. Different allometric equations relative to species (for areas dominated by Rhizophora mucronata or Bruguiera gymnorrhiza) were used for aboveground biomass, and the loss-on-ignition method was used for estimating soil carbon. The results showed that aboveground biomass ranged from 54.57 Mg ha−1 to 328.71 Mg ha−1, and soil carbon from 99.11 ± 18.35 Mg ha−1 to 133.45 ± 30.35 Mg ha−1. The total ecosystem carbon stock ranged from 402.35 ± 19.29 Mg ha−1 to 427.81 ± 18.35 Mg ha−1 at Ferney, and from 188.03 ± 30.35 Mg ha−1 to 189.72 ± 19.27 Mg ha−1 at Pointe d’Esny. Our results underscore the importance of mangrove forest stands and highlight the need for in-depth and broader spatial-scope research on blue carbon ecosystems in Mauritius.

Plastics in blue carbon ecosystems: a call for global cooperation on climate change goals

Plastics in blue carbon ecosystems: a call for global cooperation on climate change goals

Coastal wetland rehabilitation first-pass prioritisation for blue carbon and associated co-benefits

Context The Australian Government has developed a methodology for payment for carbon services provided by blue carbon ecosystems that focuses on avoided emissions and carbon additionality resulting from tidal restoration of coastal wetlands. Aims This study is a first-pass prioritisation for tidal restoration of coastal wetlands in New South Wales (NSW). Methods A pixel-based approach was applied using readily available datasets, with particular focus on watersheds above in-stream tidal barriers. Key results Many sites were identified, to investigate in detail, opportunities to restore tidal flows to coastal wetlands. More were associated with the broad coastal floodplains of northern NSW than narrower floodplains of southern NSW. Conclusions Information is needed about the location, ownership, land tenure, structure, condition and height of in-stream and over-land flow barriers, particularly in the context of rising sea levels. Decisions about managing in-stream drainage and flood mitigation infrastructure should be made cognisant of opportunities to increase blue carbon, and provide associated co-benefits, including mitigating other deleterious impacts from coastal wetland drainage. Implications Decision support tools for evaluating economic and environmental costs and benefits of tidal barriers will assist decision-makers assessing future proposals to repair or remove aging barriers, or create new tidal barriers.

Future Coastal Erosion and Wave Attenuation by Blue Carbon Ecosystem

Future Coastal Erosion and Wave Attenuation by Blue Carbon Ecosystem

干旱叠加海平面上升、氮负荷增加对河口潮汐沼泽生态系统净CO2交换的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 干旱叠加海平面上升、氮负荷增加对河口潮汐沼泽生态系统净CO2交换的影响 DOI: 10.5846/stxb202106291727 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 福建省自然科学基金重点项目（2019J02008）；福建省林业科技项目（201916）；国家自然科学基金项目（41877335） Effects of combination of drought and sea-level rise, nitrogen enrichment on net ecosystem exchange of CO2 in an estuarine tidal marsh Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:河口潮汐沼泽湿地是全球重要的蓝碳生态系统之一。海平面上升和氮负荷增加是入海河流河口湿地面临的两个主要环境问题。近年来，干旱事件频发，干旱及其与海平面上升、氮负荷增加的叠加将如何影响河口潮汐沼泽湿地生态系统净CO2交换，目前还未见报道。2020年夏秋，福建沿海经历了数月严重的气象干旱，这为揭示干旱对河口潮汐沼泽湿地生态系统净CO2交换量（NEE）和生态系统呼吸（ER）的影响提供了一个契机。分别于2019年8-10月（正常天气）和2020年8-10月（干旱天气），在闽江河口微咸水短叶茳芏沼泽湿地运用光合作用测定仪+箱法测定不同处理（对照、模拟海平面上升、模拟氮负荷增加、模拟海平面上升＋模拟氮负荷增加）短叶茳芏湿地生态系统NEE和ER，以期揭示气象干旱与海平面上升、氮负荷增加的叠加对河口沼泽湿地生态系统净CO2交换的影响。与正常天气相比，干旱天气下各处理（包含对照）的NEE均显著降低（P<0.05）；对照、海平面上升以及氮负荷增加处理样地的ER显著减少（P<0.05），海平面上升＋氮负荷增加处理ER显著增加（P<0.05）。NEE （负值）与光合有效辐射（PAR）与呈显著负相关（P<0.05）。研究发现，气象干旱降低了河口潮汐沼泽生态系统固碳规模，且这种固碳规模的降低在叠加海平面上升或氮负荷增加的情景下仍将存在。 Abstract:Estuarine tidal marsh is one of the coastal blue carbon ecosystems in the world. Sea level rise and nitrogen enrichment are two major global environmental issues facing by estuarine wetlands. In recent years, meteorological drought events often occurred. The influences of drought, and combination of drought and sea-level rise, and nitrogen enrichment on net ecosystem exchange (NEE) of CO2 of estuarine tidal marshes remain poorly studied. A novel approach using the weirs for in-situ manipulating sea level rise (including the increase of depth and duration of flooding) at relatively larger spatial scale was developed in the journal of Methods in Ecology & Evolution, however at present, the method has not been actually used in-situ to study effects of sea level rise on carbon cycle in coastal tidal marsh ecosystem. In our study, we improved the weirs and used them to manipulate the sea level rise (SR) treatment in-situ, and meanwhile applied in-situ experimental manipulations of control, nitrogen enrichment (NE), and SR+NE in a tidal brackish marsh of Cyperus malaccensis in the Minjiang River estuary, southeastern China. In summer and autumn of 2020, the meteorological drought occurred in the coastal zone of Fujian Province, which provided an opportunity to determine the effects of drought, the combination of drought and simulated sea-level rise, nitrogen enrichment on the NEE and ecosystem respiration (ER). From August to October in 2019 and 2020, the NEE and ER were measured using transparent static chamber (or black cloth shading)+Licor-6800 method. Compared with 2019 (normal year), the NEE under each treatment (including control) was significantly reduced in 2020 (drought year), and the ER in the control, the SR, and the NE was also significantly decreased in 2020. NEE was significantly negatively correlated with the photosynthetically active radiation (PAR). The results indicate that drought event can reduce net CO2 gain in estuarine tidal marshes, and this decrease still occurs under combination of drought and sea-level rise, nitrogen enrichment. 参考文献 相似文献 引证文献

Variability in blue carbon storage related to biogeochemical factors in seagrass meadows off the coast of the Korean peninsula

Coastal vegetated habitats such as mangroves, salt marshes, and seagrasses, referred to as blue carbon ecosystems, play an important role in climate change mitigation by an effective CO2 capture from atmosphere and water columns and long-term organic carbon (Corg) storage in sediments. Although seagrass meadows are considered intense carbon sinks, information on regional variability in seagrass blue carbon stock and factors influencing its capacity still remain sparse. In the present study, seagrass blue carbon storage by measuring Corg stocks in sediments and living seagrass biomass, and carbon accumulation rates (CARs) in seagrass meadows were estimated along the Korean coast. Factors affecting variability in Corg stocks were also analyzed using partial least squares (PLS) regression and principal component analysis (PCA). Projected Corg stocks in sediment, extrapolated to a depth 1 m, exhibited substantial variability among sites, ranging from 49.91 to 125.71 Mg C ha−1. The majority of Corg (96–99%) was stored in sediments, whereas the contribution of living biomass was minor. PLS regression and PCA indicated that Corg stocks in seagrass meadows are strongly associated with sediment characteristics such as dry bulk density and water and mud content. Among seagrass traits, above- to below-ground biomass ratio was significantly related to the quantity of Corg stocks in seagrass meadows. Because of the high spatial variability in Corg stocks and CARs, local and regional differences in seagrass blue carbon storage should be considered to accurately assess the climate change mitigation potential of seagrass ecosystems.

Estimation of total fine root production using continuous inflow methods in tropical mangrove forest on Pohnpei Island, Micronesia: Fine root necromass accumulation is a substantial contributor to blue carbon stocks

AbstractFine root decomposition, mortality, and production are fundamental components of belowground carbon dynamics in mangrove ecosystems. Mangroves are highly productive ecosystems with huge carbon stocks; however, information on the dynamics of submerged fine roots in mangrove soils is limited. To estimate fine root production in several sites of mangrove communities on Pohnpei Island, Micronesia, we estimated continuous inflows using a simple mass balance model to combine ingrowth core and litterbag experimental results. According to our findings, previously reported mangrove fine root production values were severely underestimated because the fine root decomposition process was disregarded during the experimental period. We estimated that annual fine root production up to 0.3 m in depth ranged from 13.8 (Bruguiera gymnorrhiza in a landward plot) to 56.3 Mg ha−1 year−1 (B. gymnorrhiza in a seaward plot). However, comparing the fine root production with respect to the unit of stem cross‐section area increase in the sample tree, the fine root production of Rhizophora spp. was greater than that of other species. The annual fine root mortality and decomposition to annual fine root production was 70%–105% and 11%–52% of annual production, respectively. The annual fine root production estimated here was much higher than that previously reported. These findings begin to quantify the contribution and importance of highly productive mangrove fine roots for carbon sequestration in blue carbon ecosystems. Moreover, this study provides new insights into the organic carbon dynamics in mangrove soils with mangrove vegetation succession.

Mapping of Subtidal and Intertidal Seagrass Meadows via Application of the Feature Pyramid Network to Unmanned Aerial Vehicle Orthophotos

Seagrass meadows are one of the blue carbon ecosystems that continue to decline worldwide. Frequent mapping is essential to monitor seagrass meadows for understanding change processes including seasonal variations and influences of meteorological and oceanic events such as typhoons and cyclones. Such mapping approaches may also enhance seagrass blue carbon strategy and management practices. Although unmanned aerial vehicle (UAV) aerial photography has been widely conducted for this purpose, there have been challenges in mapping accuracy, efficiency, and applicability to subtidal water meadows. In this study, a novel method was developed for mapping subtidal and intertidal seagrass meadows to overcome such challenges. Ground truth seagrass orthophotos in four seasons were created from the Futtsu tidal flat of Tokyo Bay, Japan, using vertical and oblique UAV photography. The feature pyramid network (FPN) was first applied for automated seagrass classification by adjusting the spatial resolution and normalization parameters and by considering the combinations of seasonal input data sets. The FPN classification results ensured high performance with the validation metrics of 0.957 overall accuracy (OA), 0.895 precision, 0.942 recall, 0.918 F1-score, and 0.848 IoU, which outperformed the conventional U-Net results. The FPN classification results highlighted seasonal variations in seagrass meadows, exhibiting an extension from winter to summer and demonstrating a decline from summer to autumn. Recovery of the meadows was also detected after the occurrence of Typhoon No. 19 in October 2019, a phenomenon which mainly happened before summer 2020.