Blue Carbon

Seagrasses comprise a substantive North American and Caribbean Sea blue carbon sink. Yet fine-scale estimates of seagrass carbon stocks, fluxes from anthropogenic disturbances, and potential gains in sedimen-tary carbon from seagrass restoration are lacking for most of the Western Hemisphere. To begin to fill this knowledge gap in the subtropics and tropics, we quantified organic carbon (C org) stocks, losses, and gains from restorations at 8 previously-disturbed seagrass sites around the Gulf of Mexico (GoM) (n = 128 cores). Mean natural seagrass C org stocks were 25.7 ± 6.7 Mg C org ha − 1 around the GoM, while mean C org stocks at adjacent barren sites that had previously hosted seagrass were 17.8 Mg C org ha − 1. Restored seagrass beds contained a mean of 38.7 ± 13.1 Mg C org ha − 1. Mean C org losses differed by anthropogenic impact type, but averaged 20.98 ± 7.14 Mg C org ha − 1. C org gains from seagrass restoration averaged 20.96 ± 8.59 Mg ha − 1. These results, when combined with the similarity between natural and restored C org content, highlight the potential of seagrass restoration for mitigating seagrass C org losses from prior impact events. Our GoM basin-wide estimates of natural C org totaled ~ 36.4 Tg for the 947,327 ha for the USA-GoM. Including Mexico, the total basin contained an estimated 37.2–37.5 Tg C org. Regional US-GoM losses totaled 21.69 Tg C org. C org losses differed significantly among anthropogenic impacts. Yet, seagrass restoration appears to be an important climate change mitigation strategy that could be implemented elsewhere throughout the tropics and subtropics.

Seagrass ecosystems provide numerous ecosystem services that support coastal communities around the world. They sustain abundant marine life as well as commercial and artisanal fisheries, and help protect shorelines from coastal erosion. Additionally, seagrass meadows are a globally significant sink for carbon and represent a key ecosystem for combating climate change. However, seagrass habitats are suffering rapid global decline. Despite recognition of the importance of “Blue Carbon,” no functioning seagrass restoration or conservation projects supported by carbon finance currently operate, and the policies and frameworks to achieve this have not been developed. Yet, seagrass ecosystems could play a central role in addressing important international research questions regarding the natural mechanisms through which the ocean and the seabed can mitigate climate change, and how ecosystem structure links to service provision. The relative inattention that seagrass ecosystems have received represents both a serious oversight and a major missed opportunity. In this paper we review the prospects of further inclusion of seagrass ecosystems in climate policy frameworks, with a particular focus on carbon storage and sequestration, as well as the potential for developing payment for ecosystem service (PES) schemes that are complementary to carbon management. Prospects for the inclusion of seagrass Blue Carbon in regulatory compliance markets are currently limited; yet despite the risks the voluntary carbon sector offers the most immediately attractive avenue for the development of carbon credits. Given the array of ecosystem services seagrass ecosystems provide the most viable route to combat climate change, ensure seagrass conservation and improve livelihoods may be to complement any carbon payments with seagrass PES schemes based on the provision of additional ecosystem services.

Abstrak Pertumbuhan lahan terbangun serta padatnya aktivitas manusia berkendara menyebabkan semakin besarnya produksi CO2 dibumi, sehingga berdampak pada penurunan kualitas udara dan efek rumah kaca. Hal ini juga ditandai dengan berkurangnya vegetasi hutan yang menyebabkan terbatasnya penyerapan karbon, ekosistem perairan memiliki kemampuan penyerapan karbonnya lebih tinggi dari penyerapan yang ada di darat sekitar 55% karbon yang ada di atmosfer dan digunakan untuk proses fotosintesis. Blue karbon merupakan penyimpan karbon terbesar yang berada disekitar pesisir pantai ditandai dengan adanya keberadaan mangrove, padang lamun, dan terumbu karang. Tujuan penelitian ini ialah memantau keberadaan ekosistem padang lamun dan terumbu karang menggunakan citra Sentinel-2A melalui transformasi algoritma lyzenga dalam mendeteksi dan mengetahui kemampuan menyimpan karbon pada pulau Kudingarenglompo. Hasil perhitungan ditemukan luasan yang lebih dominan berupa padang lamun (122ha) kemudian luasan terumbu karang mencapai (77ha) rubbel (27ha) dan pasir (18ha) serta potensi penyimpanan blue karbon tergantung kerapatan dan luas persebaran padang lamun. Tingkat uji akurasi citra Sentinel-2A dalam mendeteksi persebaran ekosistem padang lamun dan terumbu karang menghasilkan nilai sebesar 87,60%, nilai akurasi tersebut menunjukkan bahwa citra Sentinel-2A mampu digunakan dalam memantau ekosistem padang lamun dan terumbu karang atau substrat perairan dangkal. Kata kunci : padang lamun, blue karbon, lyzenga, sentinel-2A. Abstract The growth of built land as well as the density of human activity driving causes greater CO2 production on the earth, thus impacting on air quality degradation and the greenhouse effect. It is also characterized by reduced forest vegetation which also has an impact on carbon sequestration, aquatic ecosystems have a higher carbon sequestration capacity than the existing sequestration around 55% of carbon in the atmosphere and are used for photosynthesis. Blue carbon is the largest carbon storage around the coast characterized by the presence of mangroves, seagrass beds, and coral reefs. In this study monitoring the presence of seagrass and coral reef ecosystems using Sentinel-2A imagery through lyzenga algorithm transformation in detecting and knowing the ability to store carbon on the island of Kudingarenglompo. The results of the calculation found a more dominant area in the form of seagrass beds (122ha) and then the area of coral reefs reached (77ha) rubbel (27ha) and sand (18ha) and the potential for storing blue carbon depending on the density and extent of seagrass distribution. The level of testing of Sentinel-2A's image accuracy in detecting the distribution of seagrass and coral reef ecosystems yields a value of 87,60%, the accuracy value indicates that Sentinel-2A imagery is capable of being used in monitoring seagrass and coral reef or shallow water substrate ecosystems.

In this review paper, we aim to describe the potential for, and the key challenges to, applying PES projects to mangroves. By adopting a ''carbocentric approach,'' we show that mangrove forests are strong candidates for PES projects. They are particularly well suited to the generation of carbon credits because of their unrivaled potential as carbon sinks, their resistance and resilience to natural hazards, and their extensive provision of Ecosystem Services other than carbon sequestration, primarily nursery areas for fish, water purification and coastal protection, to the benefit of local communities as well as to the global population. The voluntary carbon market provides opportunities for the development of appropriate protocols and good practice case studies for mangroves at a small scale, and these may influence larger compliance schemes in the future. Mangrove habitats are mostly located in developing countries on communally or state-owned land. This means that issues of national and local governance, land ownership and management, and environmental justice are the main challenges that require careful planning at the early stages of mangrove PES projects to ensure successful outcomes and equitable benefit sharing within local communities.

The Gulf of Mexico blue carbon habitats (mangroves, seagrass, and salt marshes) form an important North American blue carbon hot spot. These habitats cover 2,161,375 ha and grow profusely in estuaries that occupy 38,000 km 2 to store substantial sedimentary organic carbon of 480.48 Tg C. New investigations around GoM for Mexican mangroves, Louisiana salt marshes and seagrasses motivated our integration of buried organic carbon to elucidate a new estimate of GoM blue carbon stocks. Factors creating this include: large GoM watersheds enriching carbon slowly flowing through shallow estuarine habitats with long residence times; fewer SE Mexican hurricanes allowing enhanced carbon storage; mangrove carbon productivity enhanced by warm southern basin winter temperatures; large Preservation reserves amongst high anthropogenic development. The dominant total GoM mangrove blue carbon stock 196.88 Tg from total mangrove extent 650,431 ha is highlighted from new Mexican data. Mexican mangrove organic carbon stock is 112.74 Tg (1st sediment meter) plus USA 84.14 Tg. Mexican mangroves vary greatly in storage, total carbon depositional depths and in sediment age (to 3500 y). We report Mexican mangrove's conservative storage fraction for the normally-compared top meter, whereas the full storage depth estimates ranging above 366.78 Tg (high productivity in very deep sediment along the central Veracruz/Tabasco coast) are not reflected in our reported estimates. Sea-grasses stock of 184.1 Tg C organic is derived from 972,327 ha areal extent (in 1st meter). The Louisiana marshes form the heart of GoM salt marsh carbon storage 99.5 Tg (in 1st meter), followed by lesser stocks in Florida, Texas, finally Mexico derived from salt marsh extent totaling 538,637 ha. Constraints on the partial estuarine fluxes given for this new data are discussed as well as widespread anthropogenic destruction of the GoM blue carbon. A new North American comparison of our GoM blue carbon stocks versus Atlantic coastal blue carbon stock estimates is presented.

Canopy height is one of the strongest predictors of biomass and carbon in forested ecosystems. Additionally, mangrove ecosystems represent one of the most concentrated carbon reservoirs that are rapidly degrading as a result of deforestation, development, and hydrologic manipulation. Therefore, the accuracy of Canopy Height Models (CHM) over mangrove forest can provide crucial information for monitoring and verification protocols. We compared four CHMs derived from independent remotely sensed imagery and identified potential errors and bias between measurement types. CHMs were derived from three spaceborne datasets; Very-High Resolution (VHR) stereophotogrammetry, TerraSAR-X add-on for Digital Elevation Measurement, and Shuttle Radar Topography Mission (TanDEM-X), and lidar data which was acquired from an airborne platform. Each dataset exhibited different error characteristics that were related to spatial resolution, sensitivities of the sensors, and reference frames. Canopies over 10 m were accurately predicted by all CHMs while the distributions of canopy height were best predicted by the VHR CHM. Depending on the guidelines and strategies needed for monitoring and verification activities, coarse resolution CHMs could be used to track canopy height at regional and global scales with finer resolution imagery used to validate and monitor critical areas undergoing rapid changes.

Carbon storage is one of the most important ecosystem services provided by kelp beds. Laminarialean kelps are widely harvested along the Warm Temperate South-eastern Pacific coast, a marine province shared by Chile and Peru. Carbon storage assessments of kelps in Peru are lacking. From a blue economy and sustainable management perspectives, information on the carbon storage of kelps is important. We conduct the first carbon storage assessment of Lessonia trabeculata in Peru and contribute to the development of biomass estimation models in order to monitor kelps using the least destructive methodologies. We chose three commonly harvested sites in San Juan de Marcona to haphazardly extract Lessonia trabeculata sporophytes using transects. Sporophyte height (m), wet biomass (kg), maximum (D) and minimum (d) holdfast disk widths (cm) were measured in the field. In the laboratory, C content was measured to calculate the best-fitting coefficients for future estimations by using allometric equations. Individual biomass was best estimated from sporophyte height through a rational model, while holdfast area (ellipse in cm2) was a good proxy of biomass with a sinusoidal model. The southernmost, least accessible, and most exposed site (Elefante) had significantly higher values of stored carbon. We estimated a carbon standing stock (from sporophytes only) of 2044 t C in these kelp beds. Nevertheless, additional and more detailed measurements will likely produce more accurate estimates both in time and space. We provide allometric equations for future carbon assessments. Our results highlight the importance carbon assessment for kelp management and blue carbon estimates and the need to develop science-based marine planning strategies.

Diminishing prospects for environmental preservation under climate change are intensifying efforts to boost capture, storage and sequestration (long-term burial) of carbon. However, as Earth's biological carbon sinks also shrink, remediation has become a key part of the narrative for terrestrial ecosystems. In contrast, blue carbon on polar continental shelves have stronger pathways to sequestration and have increased with climate-forced marine ice losses-becoming the largest known natural negative feedback on climate change. Here we explore the size and complex dynamics of blue carbon gains with spatiotemporal changes in sea ice (60-100 MtCyear −1), ice shelves (4-40 MtCyear −1 = giant iceberg generation) and glacier retreat (< 1 MtCyear −1). Estimates suggest that, amongst these, reduced duration of seasonal sea ice is most important. Decreasing sea ice extent drives longer (not necessarily larger biomass) smaller cell-sized phytoplankton blooms, increasing growth of many primary consumers and benthic carbon storage-where sequestration chances are maximal. However, sea ice losses also create positive feedbacks in shallow waters through increased iceberg movement and scouring of benthos. Unlike loss of sea ice, which enhances existing sinks, ice shelf losses generate brand new carbon sinks both where giant icebergs were, and in their wake. These also generate small positive feedbacks from scouring, minimised by repeat scouring at biodiversity hotspots. Blue carbon change from glacier retreat has been least well quantified, and although emerging fjords are small areas, they have high storage-sequestration conversion efficiencies, whilst blue carbon in polar waters faces many diverse and complex stressors. The identity of these are known (e.g. fishing, warming, ocean acidification, non-indigenous species and plastic pollution) but not their magnitude of impact. In order to mediate multiple stressors, research should focus on wider verification of blue carbon gains, projecting future change, and the broader environmental and economic benefits to safeguard blue carbon ecosystems through law.

• Anthropogenic disturbances have resulted in massive seagrass die-off. • Loss of seagrasses has resulted in organic carbon flux. • The magnitude of organic carbon loss depends on the type of seagrass disturbance. • Seagrass restoration has the potential to reverse seagrass sedimentary C losses. Seagrasses comprise a substantive North American and Caribbean Sea blue carbon sink. Yet fine-scale estimates of seagrass carbon stocks, fluxes from anthropogenic disturbances, and potential gains in sedimentary carbon from seagrass restoration are lacking for most of the Western Hemisphere. To begin to fill this knowledge gap in the subtropics and tropics, we quantified organic carbon (C org) stocks, losses, and gains from restorations at 8 previously-disturbed seagrass sites around the Gulf of Mexico (GoM) (n = 128 cores). Mean natural seagrass C org stocks were 25.7 ± 6.7 Mg C org ha −1 around the GoM, while mean C org stocks at adjacent barren sites that had previously hosted seagrass were 17.8 Mg C org ha −1. Restored seagrass beds contained a mean of 38.7 ± 13.1 Mg C org ha −1. Mean C org losses differed by anthropogenic impact type, but averaged 20.98 ± 7.14 Mg C org ha −1. C org gains from seagrass restoration averaged 20.96 ± 8.59 Mg ha −1. These results, when combined with the similarity between natural and restored C org content, highlight the potential of seagrass restoration for mitigating seagrass C org losses from prior impact events. Our GoM basin-wide estimates of natural C org totaled ~36.4 Tg for the 947,327 ha for the USA-GoM. Including Mexico, the total basin contained an estimated 37.2-37.5 Tg C org. Regional US-GoM losses totaled 21.69 Tg C org. C org losses differed significantly among anthro-pogenic impacts. Yet, seagrass restoration appears to be an important climate change mitigation strategy that could be implemented elsewhere throughout the tropics and subtropics.

Climate change and global warming have a destabilizing effect on the global environment, and governmental statutory bodies are emphasizing a reduction of emission coupled with restoration of degraded forest lands as a carbon sequestration–emission reduction (REDDþ) initiative. Asphyxiated mangrove soil, existing on the borderline of land and sea, has the highest potential to trap ‘blue carbon’; hence, plantation programs have been initiated around the tropical coasts to restore this unique habitat. This case study provides a cost–benefit and carbon sequestration analysis for planting of five mangrove species (Avicennia marina, Bruguiera sexangula, Ceriops tagal, Rhizophora mucronata and Xylocarpus moluccensis) by various methods in a 102.4-ha area at the Indian Sundarbans. It is estimated that as per the planting methods used in the current study and physio-chemical properties of the sediment, coupled with other local factors such as anthropogenic interventions, Avicennia marina planting by the ‘propagule dibbling’ method is the most cost effective (0.002Euro/survived plant), with the highest increment (97%) in organic carbon density (OCD), humic acid (100.86%) and fulvic acid (48.78%) over a period of 5 years. Survival rate was highest (82%) for Avicennia marina, planted by the ‘transplanting of nursery-grown seedlings’ method. The drain and trench method resulted in a 55% survival rate for Rhizophora mucronata, but the extra labor investment made this the costliest method (0.13Euro/survived plant) and also less carbon effective (only 85% increment of OCD in 5 years). Planting methods, sediment quality, tidal inundation and salinity variations can play a major role in blue carbon burial/sequestration in mangrove lands.