Coastal wetlands are sites of rapid carbon (C) sequestration and contain large soil C stocks. Thus, there is increasing interest in those ecosystems as sites for anthropogenic greenhouse gas emission offset projects (sometimes referred to as “Blue Carbon”), through preservation of existing C stocks or creation of new wetlands to increase future sequestration. Here we show that in the globally-widespread occurrence of diked, impounded, drained and tidally-restricted salt marshes, substantial methane (CH4) and CO2 emission reductions can be achieved through restoration of disconnected saline tidal flows. Modeled climatic forcing indicates that tidal restoration to reduce emissions has a much greater impact per unit area than wetland creation or conservation to enhance sequestration. Given that GHG emissions in tidally-restricted, degraded wetlands are caused by human activity, they are anthropogenic emissions, and reducing them will have an effect on climate that is equivalent to reduced emission of an equal quantity of fossil fuel GHG. Thus, as a landuse-based climate change intervention, reducing CH4 emissions is an entirely distinct concept from biological C sequestration projects to enhance C storage in forest or wetland biomass or soil, and will not suffer from the non-permanence risk that stored C will be returned to the atmosphere.
Blue Carbon & Sequestration
- Oceans and coasts provide a wide array of services to humans, including climate regulation, food security, and livelihoods. Managing them well is vital to human well-being as well as the maintenance of marine biodiversity and ocean-dependent economies.
- Carbon sequestration and storage is increasingly recognized as a valuable service provided by coastal vegetation. Carbon sequestered and stored by mangrove forests, tidal marshes, and seagrass meadows is known as ‘blue’ carbon. These habitats capture and store carbon within the plants themselves and in the sediment below them. When the habitats are destroyed, much of their carbon is released back to the atmosphere and ocean contributing to global climate change.
- Therefore, blue carbon ecosystem protection is becoming a greater priority in marine management and is an area of interest to scientists, policy makers, coastal communities, and the private sector including those that contribute to ecosystem degradation but also those that are looking to reduce their carbon footprint. A range of policy and management responses aim to reduce coastal ecosystem loss, including the establishment of marine protected areas (MPAs).
- This paper explores how MPA design, location, and management could be used to protect and increase carbon sequestration and ensure integrity of carbon storage through conservation and restoration activities. While additional research is necessary to validate the proposed recommendations, this paper describes much needed first steps and highlights the potential for blue carbon finance mechanisms to provide sustainable funding for MPAs.
- Coastal blue carbon activities are being implemented by a variety of countries, using different approaches. Existing regulatory regimes, including on coastal protection, are still very useful tools to protect and conserve mangroves, seagrasses and saltmarshes, and preserve their carbon value and role. These approaches suffer, however, from ‘traditional’ issues such as lack of enforcement, human and financial constraints as well as unclear or misguiding government mandates.
- Successes are witnessed using a community-based carbon project approach, ensuring high stakeholder participation via direct or indirect incentive programmes. Comprehensive coastal zone management approaches seem very promising, but success overall, and regarding carbon specifically, are yet to be reported.
- The Paris Agreement has introduced new tools which could serve as means to trigger more and better coastal adaptation and mitigation efforts. Their implementation details are, however, still under negotiation and their impacts can only be expected in a few years.
The ability of mangrove ecosystem to accumulate carbon from air, water and soil as sinker carbon is very important to reduce carbon emission in coastal ecosystem. Carbon sink represent role of mangrove ecosystem to sequestrate carbon emission is developed by a system of mangrove zone and demonstrative activities system. These paper purposes to develop system of carbon conservation in mangrove ecosystem to apply REDD program and demonstrative activities. The research methods used Komiyama equation tCer analysis and demonstrative activities formulation.
The research results showed that the carbon percentage of mangrove species between 35.97%–53.98% with Bruguiera gymnorrhiza (52.54%) and Rhizophora apiculata (52.38%) as the biggest carbon sinker of mangrove species. The carbon of mangrove ecosystem were 79.2 tonC/ha −242.2 tonC/ha, with the economic value between 396.2 US$/ha (price 5 U$/tonC) −4360.4 US$/ha, (price 18 US$). The best choice of demostrative activites in REDD framework to reduce the degradation of mangrove ecosystem was the fish pond. And the best carbon sequestration of mangrove species were Bruguiera praviflora, Rhizophora mucronta, Bruguiera sexangula, Rhizophora apiculata and Bruguiera gymnorrhiza (first mangrove zone).
The design of efficient monitoring programmes required for the assurance of offshore geological storage requires an understanding of the variability and heterogeneity of marine carbonate chemistry. In the absence of sufficient observational data and for extrapolation both spatially and seasonally, models have a significant role to play. In this study a previously evaluated hydrodynamic-biogeochemical model is used to characterise carbonate chemistry, in particular pH heterogeneity in the vicinity of the sea floor. Using three contrasting regions, the seasonal and short term variability are analysed and criteria that could be considered as indicators of anomalous carbonate chemistry identified. These criteria are then tested by imposing a number of randomised DIC perturbations on the model data, representing a comprehensive range of leakage scenarios. In conclusion optimal criteria and general rules for developing monitoring strategies are identified. Detection criteria will be site specific and vary seasonally and monitoring may be more efficient at periods of low dynamics. Analysis suggests that by using high frequency, sub-hourly monitoring anomalies as small as 0.01 of a pH unit or less may be successfully discriminated from natural variability – thereby allowing detection of small leaks or at distance from a leakage source. Conversely assurance of no leakage would be profound. Detection at deeper sites is likely to be more efficient than at shallow sites where the near bed system is closely coupled to surface processes. Although this study is based on North Sea target sites for geological storage, the model and the general conclusions are relevant to the majority of offshore storage sites lying on the continental shelf.
In Bangladesh, export-oriented shrimp farming is one of the most important sectors of the national economy. However, shrimp farming in coastal Bangladesh has devastating effects on mangrove forests. Mangroves are the most carbon-rich forests in the tropics, and blue carbon (i.e., carbon in coastal and marine ecosystems) emissions from mangrove deforestation due to shrimp cultivation are accumulating. These anthropogenic carbon emissions are the dominant cause of climate change, which in turn affect shrimp cultivation. Some adaptation strategies including Integrated Multi-Trophic Aquaculture (IMTA), mangrove restoration, and Reducing Emissions from Deforestation and forest Degradation (REDD+) could help to reduce blue carbon emissions. Translocation of shrimp culture from mangroves to open-water IMTA and restoration of habitats could reduce blue carbon emissions, which in turn would increase blue carbon sequestration. Mangrove restoration by the REDD+ program also has the potential to conserve mangroves for resilience to climate change. However, institutional support is needed to implement the proposed adaptation strategies.
Integrating spatial heterogeneity into assessments of salt marsh biogeochemistry is becoming increasingly important because disturbances that reduce plant productivity and soil drainage may contribute to an expansion of shallow ponds. These permanently inundated and sometimes prominent landscape features can exist for decades, yet little is known about pond biogeochemistry or their role in marsh ecosystem functioning. We characterized three ponds in a temperate salt marsh (MA, USA) over alternating periods of tidal isolation and flushing, during summer and fall, by evaluating the composition of plant communities and organic matter pools and measuring surface water oxygen, temperature, and conductivity. The ponds were located in the high marsh and had similar depths, temperatures, and salinities. Despite this, they had different levels of suspended particulate, dissolved, and sediment organic matter and abundances of phytoplankton, macroalgae, and Ruppia maritima. Differences in plant communities were reflected in pond metabolism rates, which ranged from autotrophic to heterotrophic. Integrating ponds into landcover-based estimates of marsh metabolism resulted in slower rates of net production (−8.1 ± 0.3 to −15.7 ± 0.9%) and respiration (−2.9 ± 0.5 to −10.0 ± 0.4%), compared to rates based on emergent grasses alone. Seasonality had a greater effect on pond water chemistry, organic matter pools, and algal abundances than tidal connectivity. Alternating stretches of tidal isolation and flushing did not affect pond salinities or algal communities, suggesting that exchange between ponds and nearby creeks was limited. Overall, we found that ponds are heterogeneous habitats and future expansion could reduce landscape connectivity and the ability of marshes to capture and store 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 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 (Corg) stocks, losses, and gains from restorations at 8 previously-disturbed seagrass sites around the Gulf of Mexico (GoM) (n = 128 cores). Mean natural seagrass Corg stocks were 25.7 ± 6.7 Mg Corg ha− 1 around the GoM, while mean Corg stocks at adjacent barren sites that had previously hosted seagrass were 17.8 Mg Corg ha− 1. Restored seagrass beds contained a mean of 38.7 ± 13.1 Mg Corg ha− 1. Mean Corg losses differed by anthropogenic impact type, but averaged 20.98 ± 7.14 Mg Corg ha− 1. Corggains from seagrass restoration averaged 20.96 ± 8.59 Mg ha− 1. These results, when combined with the similarity between natural and restored Corg content, highlight the potential of seagrass restoration for mitigating seagrass Corg losses from prior impact events. Our GoM basin-wide estimates of natural Corg 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 Corg. Regional US-GoM losses totaled 21.69 Tg Corg. Corg 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.
Over the coming century humanity may need to find reservoirs to store several trillions of tons of carbon dioxide (CO2) emitted from fossil fuel combustion, which would otherwise cause dangerous climate change if it were left in the atmosphere. Carbon storage in the ocean as bicarbonate ions (by increasing ocean alkalinity) has received very little attention. Yet, recent work suggests sufficient capacity to sequester copious quantities of CO2. It may be possible to sequester hundreds of billions to trillions of tonnes of C without surpassing post-industrial average carbonate saturation states in the surface ocean. When globally distributed, the impact of elevated alkalinity is potentially small, and may help ameliorate the effects of ocean acidification. However, the local impact around addition sites may be more acute but is specific to the mineral and technology.
The alkalinity of the ocean increases naturally because of rock weathering in which > 1.5 moles of carbon are removed from the atmosphere for every mole of magnesium or calcium dissolved from silicate minerals (e.g., wollastonite, olivine, anorthite), and 0.5 moles for carbonate minerals (e.g., calcite, dolomite). These processes are responsible for naturally sequestering 0.5 billion of CO2 tons per year. Alkalinity is reduced in the ocean through carbonate mineral precipitation, which is almost exclusively formed from biological activity. Most of the previous work on the biological response to changes in carbonate chemistry have focused on acidifying conditions. More research is required to understand carbonate precipitation at elevated alkalinity to constrain the longevity of carbon storage.
A range of technologies have been proposed to increase ocean alkalinity (accelerated weathering of limestone, enhanced weathering, electrochemical promoted weathering, ocean liming), the cost of which may be comparable to alternative carbon sequestration proposals (e.g., $20 - 100 tCO2-1). There are still many unanswered technical, environmental, social, and ethical questions, but the scale of the carbon sequestration challenge warrants research to address these.
Vegetated marine habitats are globally important carbon sinks, making a significant contribution towards mitigating climate change, and they provide a wide range of other ecosystem services. However, large gaps in knowledge remain, particularly for seagrass meadows in Africa. The present study estimated biomass and sediment organic carbon (Corg) stocks of four dominant seagrass species in Gazi Bay, Kenya. It compared sediment Corg between seagrass areas in vegetated and un-vegetated ‘controls’, using the naturally patchy occurence of seagrass at this site to test the impacts of seagrass growth on sediment Corg. It also explored relationships between the sediment and above-ground Corg, as well as between the total biomass and above-ground parameters. Sediment Corg was significantly different between species, range: 160.7–233.8 Mg C ha-1 (compared to the global range of 115.3 to 829.2 Mg C ha-1). Vegetated areas in all species had significantly higher sediment Corg compared with un-vegetated controls; the presence of seagrass increased Corg by 4–6 times. Biomass carbon differed significantly between species with means ranging between 4.8–7.1 Mg C ha-1 compared to the global range of 2.5–7.3 Mg C ha-1. To our knowledge, these are among the first results on seagrass sediment Corg to be reported from African seagrass beds; and contribute towards our understanding of the role of seagrass in global carbon dynamics.