Blue Carbon Ecosystems Research Articles

Quantifying blue carbon stocks and the role of protected areas to conserve coastal wetlands

Vegetated coastal ecosystems, in particular mangroves, tidal marshes and seagrasses are highly efficient at sequestering and storing carbon, making them valuable assets for climate change mitigation and adaptation. The state of Queensland, in northeastern Australia, contains almost half of the total area of these blue carbon ecosystems in the country, yet there are few detailed regional or state-wide assessments of their total sedimentary organic carbon (SOC) stocks. We compiled existing SOC data and used boosted regression tree models to evaluate the influence of environmental variables in explaining the variability in SOC stocks, and to produce spatially explicit blue carbon estimates. The final models explained 75 % (for mangroves and tidal marshes) and 65 % (for seagrasses) of the variability in SOC stocks. Total SOC stocks in the state of Queensland were estimated at 569 ± 98 Tg C (173 ± 32 Tg C, 232 ± 50 Tg C, and 164 ± 16 Tg C from mangroves, tidal marshes and seagrasses, respectively). Regional predictions for each of Queensland's eleven Natural Resource Management regions revealed that 60 % of the state's SOC stocks occurred within three regions (Cape York, Torres Strait and Southern Gulf Natural Resource Management regions) due to a combination of high values of SOC stocks and large areas of coastal wetlands. Protected areas in Queensland play an important role in conserving SOC assets in Queensland's coastal wetlands. For example, ~19 Tg C within terrestrial protected areas, ~27 Tg C within marine protected areas and ~ 40 Tg C within areas of matters of State Environmental Significance. Using multi-decadal (1987–2020) mapped distributions of mangroves in Queensland; we found that mangrove area increased by approximately 30,000 ha from 1987 to 2020, which led to temporal fluctuations in mangrove plant and SOC stocks. We estimated that plant stocks decreased from ~45 Tg C in 1987 to ~34.2 Tg C in 2020, while SOC stocks remained relatively constant from ~107.9 Tg C in 1987 to 108.0 Tg C in 2020. Considering the level of current protection, emissions from mangrove deforestation are potentially very low; therefore, representing minor opportunities for mangrove blue carbon projects in the region. Our study provides much needed information on current trends in carbon stocks and their conservation in Queensland's coastal wetlands, while also contributing to guide future management actions, including blue carbon restoration projects.

Current and future potential soil organic carbon stocks of vegetated coastal ecosystems and their controls in the Bohai Rim Region, China

Vegetated coastal ecosystems (VCEs) have much higher organic carbon sequestration rates and storage capacities than most other earth surface ecosystems, and thus play a vital role in blue carbon sequestration for climate change mitigation. However, soil organic carbon (SOC) stock assessment in VCEs at a large regional-scale remain problematic, and the controlling mechanisms for SOC remain poorly understood. Here, we estimated current and future SOC stocks of VCEs in the Bohai Rim Region, China at a spatial resolution of 10 m, using a data-driven method based on multi-source data; and investigated the key environmental and anthropogenic controls. The total SOC stocks and SOC density of VCEs in the Bohai Rim Region were estimated to be approximately 62.7 Tg carbon and about 68.8 Mg ha−1, respectively (in the upper 1 m of soil). We found that climate and soil salinity are the most critical environmental controls of SOC stocks within VCEs in the region. Increasing temperature and soil salinity would increase SOC decomposition and decrease plant productivity, resulting in a decrease in SOC stocks. Conversely, increasing precipitation would increase SOC stocks by reducing soil salinity. We projected that the potential losses of SOC stocks due to the combined effects of climate changes, sea-level rise, and anthropogenic disturbances would be ∼ 12.2 % between 2041 and 2060 under two Shared Socioeconomic Pathway (SSP) scenarios (SSP245 and SSP585), extending to 19.3 % between 2081 and 2100. The decreases in SOC stocks would occur mainly in the higher latitude and colder regions. The study demonstrated the potential significant reduction in SOC stocks in coastal ecosystems and provided an important framework for better understanding the blue carbon ecosystems.

Effects of Salinity on Assembly Characteristics and Function of Microbial Communities in the Phyllosphere and Rhizosphere of Salt-Tolerant Avicennia marina Mangrove Species.

It is of great significance to explore the structure and salinity response of microbial communities in salt-tolerant plants to understand the mechanisms of plant-microbe interactions. Herein, we investigated the phyllosphere and rhizosphere microbial communities of Avicennia marina, a pioneer salt-tolerant plant, at three sites with different salinities in the coastal intertidal zone. The results showed that salinity had different effects on phyllosphere and rhizosphere microbial communities and had a greater impact on bacterial communities and bacterial network interactions. The rhizosphere bacterial community alpha diversity significantly increased with increasing salinity. Moreover, the relative abundance of Proteobacteria decreased significantly, while that of Bacteroidota and Actinobacteriota, with stronger salt tolerance and nutrient utilization capacity, increased significantly. Functional prediction indicated that the microbial communities could produce catalase, peroxidase, 3-phytase, and tryptophan synthase, which may exert potential antistress and growth-promoting functions. Among them, catalase, 3-phytase, alkaline phosphatase, and acid phosphatase increased significantly in the phyllosphere and rhizosphere bacterial communities and the phyllosphere fungal community with increasing salinity. Importantly, the dominant taxa Kushneria and Bacillus, which are salt tolerant and growth promoting, were isolated from the phyllosphere and rhizosphere, respectively, and verified to have the ability to alleviate salt stress and promote the growth of rice. IMPORTANCE Avicennia marina is a pioneer salt-tolerant plant in coastal intertidal mangroves, an efficient blue carbon ecosystem. It is of great importance to explore how salinity affects the phyllosphere and rhizosphere microbial communities of A. marina. This study showed that the microbial communities in the phyllosphere and rhizosphere of A. marina had different constitutive properties, adaptive network interactions, and potential stress-promoting functions. Furthermore, the dominant bacteria Kushneria and Bacillus were obtained from the phyllosphere and rhizosphere, respectively, and their coculture with rice could effectively alleviate salt stress and promote rice growth. Additionally, the effects of salinity changes on microbial community structure, associations, and functional potential in the phyllosphere and rhizosphere of A. marina were observed. This study has enriched our understanding of the microbial community structure, function, and ecological stability of mangrove species in coastal intertidal zones and has practical significance for improving crop yield by using salt-tolerant plant microbiomes.

Importance of Blue Carbon in Mitigating Climate Change and Plastic/Microplastic Pollution and Promoting Circular Economy

Blue carbon has made significant contributions to climate change adaptation and mitigation while assisting in achieving co-benefits such as aquaculture development and coastal restoration, winning international recognition. Climate change mitigation and co-benefits from blue carbon ecosystems are highlighted in the recent Intergovernmental Panel on Climate Change Special Report on Ocean and Cryosphere in a Changing Climate. Its diverse nature has resulted in unprecedented collaboration across disciplines, with conservationists, academics, and politicians working together to achieve common goals such as climate change mitigation and adaptation, which need proper policy regulations, funding, and multi-prong and multi-dimensional strategies to deal with. An overview of blue carbon habitats such as seagrass beds, mangrove forests, and salt marshes, the critical role of blue carbon ecosystems in mitigating plastic/micro-plastic pollution, as well as the utilization of the above-mentioned blue carbon resources for biofuel production, are critically presented in this research. It also highlights the concerns about blue carbon habitats. Identifying and addressing these issues might help preserve and enhance the ocean’s ability to store carbon and combat climate change and mitigate plastic/micro-plastic pollution. Checking out their role in carbon sequestration and how they act as the major carbon sinks of the world are integral parts of this study. In light of the global frameworks for blue carbon and the inclusion of microalgae in blue carbon, blue carbon ecosystems must be protected and restored as part of carbon stock conservation efforts and the mitigation of plastic/micro-plastic pollution. When compared to the ecosystem services offered by terrestrial ecosystems, the ecosystem services provided by coastal ecosystems, such as the sequestration of carbon, the production of biofuels, and the remediation of pollution, among other things, are enormous. The primary purpose of this research is to bring awareness to the extensive range of beneficial effects that can be traced back to ecosystems found in coastal environments.

Geochemical properties of blue carbon sediments through an elevation gradient: study of an anthropogenically impacted coastal lagoon

Global research is showing that coastal blue carbon ecosystems are vulnerable to climate change driven threats including accelerated sea-level rise and prolonged periods of drought. Furthermore, direct anthropogenic impacts present immediate threats through deterioration of coastal water quality, land reclamation, long-term impact to sediment biogeochemical cycling. These threats will invariably alter the future efficacy of carbon (C) sequestration processes and it is imperative that currently existing blue carbon habitats be protected. Knowledge of underlying biogeochemical, physical and hydrological interactions occurring in functioning blue carbon habitats is essential for developing strategies to mitigate threats, and promote conditions to optimise C sequestration/storage. In this current work, we investigated how sediment geochemistry (0–10 cm depth) responds to elevation, an edaphic factor driven by long-term hydrological regimes consequently exerting control over particle sedimentation rates and vegetation succession. This study was performed in an anthropogenically impacted blue carbon habitat along a coastal ecotone encompassing an elevation gradient transect from intertidal sediments (un-vegetated and covered daily by tidal water), through vegetated salt marsh sediments (periodically covered by spring tides and flooding events), on Bull Island, Dublin Bay. We determined the quantity and distributions of bulk geochemical characteristics in sediments through the elevation gradient, including total organic carbon (TOC), total nitrogen (TN), total metals, silt, clay, and also, 16 individual polyaromatic hydrocarbon’s (PAH’s) as an indication of anthropogenic input. Elevation measurements for sample sites were determined on this gradient using a LiDAR scanner accompanied by an IGI inertial measurement unit (IMU) on board a light aircraft. Considering the gradient from the Tidal mud zone (T), through the low-mid marsh (M) to the most elevated upper marsh (H), there were significant differences between all zones for many measured environmental variables. The results of significance testing using Kruskal–Wallis analysis revealed, that %C, %N, PAH (µg/g), Mn (mg/kg), TOC:NH4+ and pH are significantly different between all zones on the elevation gradient. The highest values for all these variables exists (excluding pH which followed a reverse trend) in zone H, decreasing in zone M and lowest in the un-vegetated zone T. TC content is 16 fold higher overall in vegetated (3.43 -21.84%) than uninhabited (0.21–0.56%) sediments. TN was over 50 times higher (0.24–1.76%), more specifically increasing in % mass on approach to the upper salt marsh with distance from the tidal flats sediments zone T (0.002–0.05%). Clay and silt distributions were greatest in vegetated sediments, increasing in % content towards upper marsh zones The retention of water, metals, PAHs, mud, chloride ions, NH4+, PO43− and SO42− increased with elevated C concentrations, concurrently where pH significantly decreased. Sediments were categorized with respect to PAH contamination where all SM samples were placed in the high polluted category. The results highlight the ability of Blue C sediments to immobilise increasing levels of C, N, and metals, and PAH with over time and with both lateral and vertical expansion. This study provides a valuable data set for an anthropogenically impacted blue carbon habitat predicted to suffer from sea-level rise and exponential urban development.Graphical abstractSummarized results from this study demonstrating the geochemical changes through an elevation gradient, with a transect encompassing intertidal sediments through supratidal salt marsh sediments within Bull Island’s blue carbon lagoon zones.

Communicating Blue Carbon Science Across the Indo-Pacific Region Through Capacity Building Fellowships

Communicating the value of blue carbon ecosystems requires sound knowledge of biology, remote sensing, carbon assessment, policy, and approaches to restoration. We describe a successful training program where young professionals from developing countries are hosted in Australia and taught to communicate blue carbon science to researchers, policy makers, and the public. Across several programs, some run during the COVID-19 pandemic, participants increased their knowledge of important areas of blue carbon science by 58% to 74%. This integrative teaching platform gives participants the knowledge and skills needed to help solve the major challenges to the marine environment in their home countries.

Changes in Mangrove Blue Carbon under Elevated Atmospheric CO 2

While there is consensus that blue carbon ecosystems, such as mangroves, have an important role in mitigating some aspects of global climate change, little is known about mangrove carbon cycling under elevated atmospheric CO 2 concentrations ( e CO 2 ). Here, we review studies in order to identify pathways for how e CO 2 might influence mangrove ecosystem carbon cycling. In general, e CO 2 alters plant productivity, species community composition, carbon fluxes, and carbon deposition in ways that enhance mangrove carbon storage with e CO 2 . As a result, a negative feedback to climate change exists whereby e CO 2 adds to mangrove’s ability to sequester additional carbon, which in turn reduces the rate by which CO 2 builds. Furthermore, e CO 2 affects warming and sea-level rise (SLR) through alternate pathways, which coinfluence the mangrove response in both antagonistic (i.e., warming = greater carbon loss to decomposition) and synergistic (i.e., SLR = greater soil carbon burial) ways. e CO 2 is projected to become a more prominent driver in the future before reaching a steady state. However, given the complexity of the interactions of biological and environmental factors with e CO 2 , long-term field observations and in situ simulation experiments can help to better understand the mechanisms for proper model initialization to predict future changes in mangrove carbon sequestration.

Spatiotemporal dynamics and geo-environmental factors influencing mangrove gross primary productivity during 2000–2020 in Gaoqiao Mangrove Reserve, China

BackgroundMangrove forests are a significant contributor to the global carbon cycle, and the accurate estimation of their gross primary productivity (GPP) is essential for understanding the carbon budget within blue carbon ecosystems. Little attention has been given to the investigation of spatiotemporal patterns and ecological variations within mangrove ecosystems, as well as the quantitative analysis of the influence of geo-environmental factors on time-series estimations of mangrove GPP. MethodsThis study explored the spatiotemporal dynamics of mangrove GPP from 2000 to 2020 in Gaoqiao Mangrove Reserve, China. A leaf area index (LAI)-based light-use efficiency (LUE) model was combined with Landsat data on Google Earth Engine (GEE) to reveal the variations in mangrove GPP using the Mann-Kendall (MK) test and Theil-Sen median trend. Moreover, the spatiotemporal patterns and ecological variations in mangrove ecosystems across regions were explored using four landscape indicators. Furthermore, the effects of six geo-environmental factors (species distribution, offshore distance, elevation, slope, planar curvature and profile curvature) on GPP were investigated using Geodetector and multi-scale geo-weighted regression (MGWR). ResultsThe results showed that the mangrove forest in the study area experienced an area loss from 766.26 ​ha in 2000 to 718.29 ​ha in 2020, mainly due to the conversion to farming, terrestrial forest and aquaculture zones. Landscape patterns indicated high levels of vegetation aggregation near water bodies and aquaculture zones, and low levels of aggregation but high species diversity and distribution density near building zone. The mean value of mangrove GPP continuously increased from 6.35 ​g ​C·m−2·d−1 in 2000 to 8.33 ​g ​C·m−2·d−1 in 2020, with 23.21% of areas showing a highly and significantly increasing trend (trend value ​> ​0.50). The Geodetector and MGWR analyses showed that species distribution, offshore distance and elevation contributed most to the GPP variations. ConclusionsThese results provide guidelines for selecting GPP products, and the combination of Geodetector and MGWR based on multiple geo-environmental factors could quantitatively capture the mode, direction, pathway and intensity of the influencing factors on mangrove GPP variation. The findings provide a foundation for understanding the spatiotemporal dynamics of mangrove GPP at the landscape or regional scale.

Saltmarsh Carbon Stock Changes under Combined Effects of Vegetation Succession and Reclamation

Blue carbon ecosystems have been widely recognized for their carbon sequestration function to mitigate climate changes. However, both natural processes (e.g., interspecific competition) and human activities could alter the ability of blue carbon storage. To clarify the impacts of vegetation succession and reclamation on carbon stock changes, field investigation and laboratory analysis were conducted in a saltmarsh within Hangzhou Bay. Remote sensing data indicated a zonation pattern: the exotic speciesSpartina alternifloraencroached into the native speciesScirpus mariqueterat a rate of 3.51 km2a−1, butS. mariqueterexpanded to the front bare mudflat at a rate of 2.51 km2a−1. The carbon stock (1 m in depth) was found to be 85.37 Mg C ha−1for the exotic species, 56.52 Mg C ha−1for the native species, and 39.78 Mg C ha−1for the bare mudflat. The carbon burial rate varied among 3 habitats, from 0.63 Mg C ha−1a−1in the bare mudflat to 1.39 to 1.59 Mg C ha−1a−1in the vegetation sites. Within the study area, vegetation succession contributed an additional 4,858 Mg of organic carbon between 2017 and 2020 to the carbon pool. The organic carbon content of the reclamation site showed a considerable reduction, from 8.51 g kg−1to 3.34 g kg−1after 2 years of reclamation, resulting in an emission of 21.61 Mg C ha−1. Overall, the vegetation succession increased the carbon stock of the region while reclamation caused a net carbon loss in the saltmarshes. These findings can enrich the cognition to promote blue carbon management in coastal zones.

Recovery of Mangrove Ecosystem Carbon Stocks Through Reforestation at Abandoned Shrimp Pond in Southeast Thailand

Mangrove forests play an important role in the carbon cycle by sequestering atmospheric CO2and storing it as carbon in plant materials and sediments. We evaluated the ecosystem carbon stocks and carbon accumulation rates of an 18-year mangrove reforestation site located in abandoned shrimp ponds of Southeast Thailand. Consequently, carbon stocks in biomass and soil increased drastically through reforestation compared to those in nonplanted area (NPA). Soil carbon stocks at 1.0- and 2.0-m depth after 18 years were approximately 2.1 times and 1.8 times higher than those in NPA. Soil carbon stocks at 1.0-m soil depth increased gradually across the mangrove chronosequence over 18 years. Ecosystem carbon stocks at the 18-year site were 179.6 ± 40.5 Mg C·ha−1to 1-m soil depth and 325.0 ± 77.6 Mg C·ha−1to 2-m soil depth, which was higher compared to those in NPA [69.3 ± 8.0 Mg C·ha−1(1 m) and 157.8 ± 10.9 Mg C·ha−1(2 m)]. The ecosystem carbon stocks were lower than the global mean value, but the carbon accumulation rate had a comparatively high value. The total carbon accumulation rate after 18 years was 9.9 Mg C·ha−1·year−1to soil 1-m depth and 18.1 Mg C·ha−1·year−1to 2-m depth. Moreover, correlation relationships between soil carbon stock and physicochemical properties such as pH, electrical conductivity, redox potential, bulk density, elapsed year, and temperature in NPA and reforestation sites were confirmed. Therefore, the recovery of carbon stocks through mangrove reforestation in abandoned shrimp pond can contribute to blue carbon ecosystem restoration as nature-based solutions.

Blue carbon stock in sediments of mangroves and seagrass ecosystems at Southeast Sulawesi, Indonesia

AbstractCoastal ecosystems store approximately 80% of carbon in sediments, which could be emitted due to degradation and deforestation. Therefore, protecting and managing these ecosystems are crucial for climate change mitigation. This study aims to determine sediment bulk density (SBD), sediment organic carbon (SOC) concentration, and sediment carbon stocks (SCS) in mangroves and seagrasses, and to elucidate how the protection scheme impacts them. We collected four sediment cores of 100 cm each from protected and unprotected mangrove areas and three sediment cores of 80 cm each from unprotected and protected seagrass areas. The average SBD in mangroves was 0.48 g cm−3 in protected areas and 0.55 g cm−3 in unprotected areas, while the average SBD in seagrass was 0.79 g cm−3 in protected areas and 0.85 g cm−3 in unprotected areas. The average SOC in mangroves was 8.65% in protected areas and 8.63% in unprotected areas, while the average SOC in seagrass was 5.89% and 6.25% in protected and unprotected areas, respectively. The average SCS in the protected area was 381 and 363 Mg C ha−1 in the mangrove and seagrass ecosystems, respectively. On the other hand, the average SCS in the unprotected areas was 449 and 422 Mg C ha−1 in mangroves and seagrass ecosystems, respectively. Although we did not find any significant differences in SCS between protected and unprotected ecosystems regardless of ecosystem types, the conservation management of blue carbon ecosystems is still needed to avoid future carbon emissions.

Rapid carbon accumulation at a saltmarsh restored by managed realignment exceeded carbon emitted in direct site construction.

Increasing attention is being paid to the carbon sequestration and storage services provided by coastal blue carbon ecosystems such as saltmarshes. Sites restored by managed realignment, where existing sea walls are breached to reinstate tidal inundation to the land behind, have considerable potential to accumulate carbon through deposition of sediment brought in by the tide and burial of vegetation in the site. While this potential has been recognised, it is not yet a common motivating factor for saltmarsh restoration, partly due to uncertainties about the rate of carbon accumulation and how this balances against the greenhouse gases emitted during site construction. We use a combination of field measurements over four years and remote sensing to quantify carbon accumulation at a large managed realignment site, Steart Marshes, UK. Sediment accumulated rapidly at Steart Marshes (mean of 75 mm yr-1) and had a high carbon content (4.4% total carbon, 2.2% total organic carbon), resulting in carbon accumulation of 36.6 t ha-1 yr-1 total carbon (19.4 t ha-1 yr-1 total organic carbon). This rate of carbon accumulation is an order of magnitude higher than reported in many other restored saltmarshes, and is somewhat higher than values previously reported from another hypertidal system (Bay of Fundy, Canada). The estimated carbon emissions associated with the construction of the site were ~2-4% of the observed carbon accumulation during the study period, supporting the view that managed realignment projects in such settings may have significant carbon accumulation benefits. However, uncertainties such as the origin of carbon (allochthonous or autochthonous) and changes in gas fluxes need to be resolved to move towards a full carbon budget for saltmarsh restoration.

Prediction of the landscape pattern of the Yancheng Coastal Wetland, China, based on XGBoost and the MCE-CA-Markov model

Coastal wetland is a crucial part of the blue carbon ecosystem, having unique structural characteristics and serving both land and water functions. These areas also offer strong carbon sequestration and storage capacity. However, human activities and climate change have led to an ongoing decline in wetland areas. As an important wetland reserve in China, the coastal wetlands of Yancheng, Jiangsu Province, bring together a great number of water resources, land resources, biological resources, landscape resources, mineral resources, energy resources, and many other resources. However, in recent years, the coastal wetlands of Yancheng have also faced a continuous reduction in area. In this study, an integrated model of the Extreme Gradient Boosting (XGBoost) algorithm and multi-criteria evaluation-cellular automata-Markov (MCE-CA-Markov) model was designed to determine the importance of the driving factors of landscape pattern change and predict the landscape pattern of coastal wetlands in 2025, based on the analysis of landscape pattern changes in 2005, 2010, 2015, and 2020 in Yancheng coastal wetlands, Jiangsu Province. The results showed that the landscape configuration of coastal wetlands in Yancheng changed significantly during 2005–2020. The total natural wetland landscape area declined steadily over that 15-year span, showing a total decrease of 2.971×104 ha; on the contrary, the artificial wetlands increased. The analysis of the driving factors of wetland damage showed that gross domestic product (GDP), distance to roads, and average precipitation were the key factors. Based on this model, the natural wetland landscape of Yancheng’s coastal wetlands is predicted to decline sharply in 2025, and the wetland salt marsh vegetation will be extensively converted to aquaculture and agricultural land. Constructed land is predicted to increase significantly, and the trend of urban expansion is obvious. The study concludes with practical suggestions for the sustainable development and ecological conservation of the Yancheng coastal wetland ecosystem based on the predicted scenario.

Blue carbon: A new paradigm of mangrove conservation and management in Indonesia

Indonesia is the largest archipelagic country in the world and has vast natural resources. In the maritime sector, efforts to realize the sustainability of natural resources in coastal ecosystems have focused on mangroves and seagrass meadows, also known as blue carbon ecosystems, that have an important role in regulating the Earth's climate. The need for ecosystem-based climate change mitigation combined with economic recovery and improved environment conditions has shifted the motivation and escalated mangrove restoration efforts in Indonesia. As the richest mangrove nation with the greatest mangrove carbon stocks in the world, recently Indonesia has taken significant steps in the land use sector to reduce emissions by acknowledging the ‘true’ value of mangrove carbon and setting priorities for mangrove conservation and restoration within Indonesia’s climate actions. This paper reviews opportunities and challenges in mainstreaming mangrove blue carbon into policy in Indonesia. We evaluate the gaps in regulations and policies and propose pathways for the national blue carbon action. As mangroves are embedded in both forestry and marine sectors and the responsibilities for management lies within several government ministries, an integrated framework is suggested to support the national blue carbon strategy. The Indonesia Blue Carbon Strategy Framework (IBCSF) encompasses three main elements that should be considered in order to address challenges and seize opportunities in blue carbon: coordination, policy and funding.

High-Resolution Mapping of Seagrass Biomass Dynamics Suggests Differential Response of Seagrasses to Fluctuating Environments

Seagrass beds are major blue carbon ecosystems. Climate change-associated factors may change the seagrass community and affect the capacity of carbon sequestration. To explore the possible effects of warming, higher precipitation levels and/or sea level rise on seagrasses, the spatial and seasonal dynamics in shallow seagrass beds comprising the late-successional seagrass Thalassia hemprichii and the early-successional seagrass Halodule uninervis were tracked. The high-resolution mapping of seagrass biomass dynamics showed that T. hemprichii was the dominant species in the study sites year round, as the space occupation by the larger seagrass T. hemprichii was more efficient than that by the smaller seagrass H. uninervis. The space occupation by both species in the low-elevation site was more efficient than in the high-elevation site. In the low-elevation site, while the dominance of the faster growing seagrass H. uninervis was increasing, the dominance of T. hemprichii was decreasing. This suggested that the carbon sequestration capacity of the seagrass beds will decrease, as T. hemprichii was capable of storing more carbon in the sediments. In the high-elevation site, however, the distribution of both species was distinct and showed a clear seasonal succession. The dominance of H. uninervis moved to shallower water in the wet season and then moved back to deeper water in the dry season. Our observations suggested that four possible mechanisms might be involved in the dominance shift in the shallow seagrass beds: (1) the deeper water in the low-elevation site or the higher precipitation levels in the wet season might reduce the drought stress of H. uninervis at low tide and enhance the competition of H. uninervis over T. hemprichii; (2) the growth of H. uninervis might be stimulated more by the flushing of land-based nutrients caused by the higher precipitation rates in the wet season; (3) in the high-elevation site, the faster flow velocity and frequently disturbed sediments in the dry season might constrain the further expansion of H. uninervis to shallower water; (4) the faster flow velocity in the high-elevation site might reduce the impacts of periphyton overgrowth on T. hemprichii and maintain the dominance of T. hemprichii in the community. Our results suggest seagrasses will not necessarily respond to fluctuating environments in the same way in the coming decades.

Blue carbon sinks in South Africa and the need for restoration to enhance carbon sequestration

Blue carbon ecosystems (mangroves, salt marshes, and seagrasses) contribute towards climate change mitigation because they are efficient at sequestering atmospheric CO2 into long-term total ecosystem carbon stocks. Destruction or disturbance therefore reduces sink capacity and leads to significant CO2 emissions. This study reports the first national estimates of: 1) total carbon storage, 2) CO2 emissions from anthropogenic activities, 3) the potential for restoration to enhance carbon sequestration for blue carbon ecosystems in South Africa. Mangrove ecosystems have the greatest carbon storage per unit area (253–534 Mg C ha−1), followed by salt marshes (100–199 Mg C ha−1) and seagrasses (45–144 Mg C ha−1). Salt marshes are the most extensive and contribute 67 % to the national carbon stock of 4000 Gg C. Since 1930, 6500 ha has been lost across all blue carbon ecosystems (26 % of the natural extent), equivalent to losing 1086 Gg C from the national carbon stock. Historic CO2 emissions were estimated at an average rate of 30,266 t CO2e yr−1. Despite losses, a total of 3998 ha could be restored to increase carbon sequestration and CO2 removals of 14,845 tCO2e.yr−1. Extractive activities have declined rapidly in recent decades, but abiotic pressures on estuarine ecosystems (flow modification, reduced water quality, and artificial breaching) have been increasing. There is an urgent need to quantify the potential impact of these pressures and include them in estuarine management and restoration plans. Blue carbon ecosystems cover a relatively small area in South Africa, but they are valued for their multiple ecosystem services that contribute towards climate change adaptation and biodiversity co-benefits. These ecosystems need to be included in national policies driving climate change response in the Agriculture, Forestry and Other Land-Use (AFOLU) sector, such as incorporating them into the wetland subcategory of the national GHG inventory.

Developing seagrass index for long term monitoring of Zostera japonica seagrass bed: A case study in Yellow River Delta, China

Seagrass beds offer unique and vital ecological services as an important blue carbon ecosystem in coastal wetlands. Zostera japonica is an intertidal seagrass species native to eastern Asia and is one of the most widely distributed seagrass species in China. However, little is known on the long-term variations of Z. japonica extents. Automatic mapping method for Z. japonica seagrass beds is in urgent need to fill this knowledge gap. In this study, we proposed a new SeaGrass Index (SGI) for automatic and rapid mapping of Z. japonica based on time-series Landsat satellite imagery, aiming to alleviate the influence of tidal inundation and enhance the separability from other coastal cover types. The SGI considers both spectral and phenological characteristics of Z. japonica, as well as the spatial location of Z. japonica. We took the Yellow River Delta (YRD), China as our study area, where Z. japonica was first discovered and reported in 2015. Based on SGI, Z. japonica extents during 1985–2018 were extracted using multi-Otsu thresholding algorithm. Accuracy assessments based on field investigations and high-resolution imagery showed that SGI successfully separated seagrass beds from other cover types, especially intertidal salt marshes, with overall accuracies > 95%, producer’s accuracies > 90% and user’s accuracies > 94%. Our study provides the first long-term maps of seagrass beds in YRD. The area of Z. japonica showed large variations during 1985–2018, ranging from 149 ha in 2005–2006 to 1302.9 ha in 2011–2012. The spatial distribution of Z. japonica varied with the morphological change of the estuary caused by river channel shifts. Since 2011, Z. japonica seagrass beds have undergone area degradation due to the invasion of S. alterniflora. The area was only 332.3 ha in 2017–2018. Coastal erosion and extreme climate events such as drought and typhoon might also explain degradation of seagrass beds in YRD. We expect that the SGI will advance automatic and rapid mapping methods for intertidal seagrass beds, and the Z. japonica maps will provide a baseline data for restoration and management of seagrasses at regional scale.

Evolution of blue carbon management policies in China: review, performance and prospects

ABSTRACT Since 1982, China’s blue carbon management policies have made significant contributions to blue carbon’s development. Blue carbon is carbon captured and stored by marine ecosystems and it plays an important role in addressing climate change. Analyzing the evolution of blue carbon management policy is necessary to understand its potential to contribute to climate action, and to improve its management and maximize its effectiveness. This paper considers these issues in China. It used content analysis and ROSTCM6 software to empirically analyze 82 blue carbon management policy documents from China. The evolution of relevant policies and their performance is as follows: First, policy focus has gradually shifted from protecting blue carbon ecosystems to increasing blue carbon stocks; second, policy participants became increasingly diversified; and third, the policy approach has changed from simple protection to comprehensive, integrated land use – marine system management. Although the Chinese government has made progress in blue carbon management policies, it still faces many challenges including blue carbon ecosystem protection; legal status; trading mechanisms; and international cooperation. The development of future blue carbon management policy should focus on optimizing the land use structure of coastal zones, on promoting environmental legislation highlighting blue carbon issues, on supporting the establishment of blue carbon trading mechanisms, and on strengthening its international cooperation in this arena. Key policy insights China’s blue carbon management approaches shows that relevant policies contribute greatly to addressing climate change and sustainable development. This provides new theoretical support to promote future development of blue carbon management policies. Establishing a blue carbon trading mechanism provides economic incentives for its management. Blue carbon’s property rights, accounting standards, and trading entities need to be further clarified. A detailed legal definition of blue carbon is needed to ensure that appropriate penalties are imposed for the destruction of blue carbon ecosystems.

The Evolution of Blue Carbon Science

‘Blue carbon’ was coined over a decade ago to describe the contribution of mangroves, seagrasses, and tidal marshes to carbon drawdown in coasts and oceans, concomitantly attracting attention of policy-makers and resource managers to their potential as a natural climate solution. Here, we explore the emergence and evolution of this relatively new research field through bibliometrics approaches to investigate patterns and trends in scientific publications through time. Our aim was to understand the evolution of blue carbon science, from where we came from and where we are now. We analysed 1,729 papers from 5,763 authors. Overall, the carbon-sink capacity of these ecosystems has been recognised long before the term ‘blue carbon’ was coined; with an annual percentage growth rate of 20% y− 1. Research attention was highest for mangroves (~ 38% of publications), followed by saltmarshes (~ 22%), and seagrasses (~ 18%); while ~ 16% of the studies included two or more blue carbon ecosystems and 5% of the studies focused on other ecosystems. The citation burst analysis showed that, in the 1990s, the hot topic (i.e., fast-growing topic) was related to the overall flux and dynamics of carbon, with a recent transition to the role of coastal vegetation to climate change mitigation from 2009. The term ‘blue carbon’ became a hot topic in 2017, with the strongest citation burst between 2017 and 2020. This bibliometric study draws the patterns and trends of blue carbon science and indicate that this field is evolving through time to focus more on the blue carbon role as nature climate solutions.

Pathways for Understanding Blue Carbon Microbiomes with Amplicon Sequencing.

The capacity of Blue Carbon Ecosystems to act as carbon sinks is strongly influenced by the metabolism of soil-associated microbes, which ultimately determine how much carbon is accumulated or returned to the atmosphere. The rapid evolution of sequencing technologies has facilitated the generation of tremendous amounts of data on what taxa comprise belowground microbial assemblages, largely available as isolated datasets, offering an opportunity for synthesis research that informs progress on understanding Blue Carbon microbiomes. We identified questions that can be addressed with a synthesis approach, including the high variability across datasets, space, and time due to differing sampling techniques, ecosystem or vegetation specificity, and the relationship between microbiome community and edaphic properties, particularly soil carbon. To address these questions, we collated 34 16S rRNA amplicon sequencing datasets, including bulk soil or rhizosphere from seagrass, mangroves, and saltmarshes within publicly available repositories. We identified technical and theoretical challenges that precluded a synthesis of multiple studies with currently available data, and opportunities for addressing the knowledge gaps within Blue Carbon microbial ecology going forward. Here, we provide a standardisation toolbox that supports enacting tasks for the acquisition, management, and integration of Blue Carbon-associated sequencing data and metadata to potentially elucidate novel mechanisms behind Blue Carbon dynamics.