Blue carbon

Overview

Historically the ocean and terrestrial forest ecosystems have been major natural carbon (C) sinks. New research on the role of coastal ecosystems and their potential to highly efficient C sinks, and led to the scientific recognition of the term “Blue Carbon”. ^[2] “Blue Carbon” designates carbon that is fixed via ocean and coastal ecosystems, rather than traditional land ecosystems, like forests. ALTHOUGH the ocean’s vegetated habitats cover less than 0.5% of the seabed , They Are Responsible for more than 50%, and Potentially up to 70% of all carbon storage in ocean sediments. ^[2] Mangroves , salt marshes and seagrasses0.05% of the plant biomass on land. Despite their small footprint, they can store a comparable amount of carbon per year and are highly efficient carbon sinks. Seagrass, mangrove and salt marshes can capture carbon dioxide ( CO ₂ ) from the atmosphere by sequestering the C in their underlying sediments, in underground and below ground biomass, and in dead biomass. ^[3] In plant biomass such as leaves, stems, golden roots, blue carbon can be sequestered for years to decades, and for millions of years in underlying plant sediments. Current estimates of long-term blue carbon are of variable, and research is ongoing.^[3] Although vegetated coastal ecosystems cover less area and have less aboveground biomass thanterrestrial plants they have the potential to impact longterm C sequestration, particularly in sediment sinks. ^[2] One of the main concerns with Blue Carbon is the rate of loss of these important marine ecosystems is much higher than any other ecosystem on the planet, even compared to rainforests. Current estimates suggest a loss of 2-7% per year, which is not only lost carbon sequestration, but also is important for coastal protection, coastal protection, and health. ^[2]

Types of blue carbon ecosystems

Seagrass

Seagrass are a group of about 60 angiosperm species-have That year adapté to aquatic life, and can grow in meadows along the shores of all continents except Antarctica . ^[4] Seagrass meadows form in maximum depths of up to 50m, depending on water quality and availability, and can include up to 12 different species in one meadow. ^[4] These seagrasses are highly productive habitats, including sediment stabilization, habitat and biodiversity , and water and nutrient sequestration. ^[5] The current documented seagrass area is 177,000 km ², but are thought to be under the influence of a large number of people. ^[4] Most common estimates are 300,000 to 600,000 km ² , with up to 4,320,000 km ² suitable for seagrass habitat worldwide. ^[6] Although seagrass makes up only 0.1% of the ocean floor, it accounts for approximately 10-18% of the total oceanic carbon burial. ^[7] Currently, global seagrass is estimated to be 19.9 Pg (gigaton, or trillion tons) of organic carbon. ^[7] Carbon mainly accumulates in marine sediments , which are anoxicand thus continually preserving organic carbon from decadal-millennial time scales. High accumulation rates, low oxygen, low sediment conductivity and low microbial decomposition rates all promote carbon burial and carbon accumulation in these coastal sediments. ^[4] Compared to terrestrial habitats that lose carbon stocks as CO ₂ during decomposition or by disturbances like fires or deforestation, marine carbon sinks can retain C for much longer time periods. Carbon sequestration rates in seagrass meadows vary depending on the species, characteristics of the sediment, and depth of the habitats, but on average the carbon burst is approximately 138 g C m ^-2 yr ^-1 .^[3] Seagrass habitats are threatened by coastal eutrophication , increased seawater temperatures, ^[4] increased sedimentation and coastal development, ^[3]and photosynthesis . Seagrass loss has accelerated over the past few decades, from 0.9% per year to 1990 to 7% per year in 1990, with about 1/3 of global loss since WWII. ^[8] Scientists encourage the protection of these ecosystems and their ecosystems.

Mangrove

Mangroves are woody halophytes that form intertidal forests and provide many important ecosystem services including coastal protection, nursery grounds for coastal fish and crustaceans, forest products, recreation, nutrient filtration and carbon sequestration . ^[9] Currently, they are found in 123 countries, with 73 identified species. ^[10] They grow along coastlines in subtropicaland tropical waters, depending on temperature, but also vary with precipitation, tides, waves and water flow. ^[11]Because they grow at the intersection between land and sea, they have unique adaptations including aerial roots, viviparous embryos, and highly efficient nutrient retention mechanisms. ^[12] Mangroves cover approximately 150,000 km ² in the last 25 years, mainly due to coastal development and land conversion. Mangrove deforestation is slowing, from 1.04% loss per year in the 1980s to 0.66% loss in the early 2000s, ^[10] as research and understanding of mangrove benefits increased. Mangrove forests are responsible for approximately 10% of global carbon burial, ^[13] with an estimated carbon burial rate of 174 g C m^-2 yr ^-1. ^[12] Mangroves, like seagrasses, have potential for high levels of carbon sequestration. They account for 3% of the global carbon sequestration by tropical forests and 14% of the global coastal ocean’s carbon burial. ^[11] Mangroves are naturally disturbed by floods, tsunamis , coastal storms like cyclones and hurricanes , lightning, disease and pests, and changes in water quality or temperature. ^[12] Although they are resilient to many of these natural disturbances, they are highly susceptible to human impacts including urban development, aquaculture , mining, and overexploitation of shellfish, crustaceans, fish and timber. ^[10] [12] Mangroves provide globally important ecosystem services and carbon sequestration and are thus an important habitat to conserve and repair when possible.

Marsh

Marshes , intertidal ecosystems dominated by herbaceous vegetation, can be found globally on coastlines from the Arctic to the subtropics. In the tropics, marshes are replaced by mangroves as the dominant coastal vegetation. ^[14] Marshes have high productivity, with a large portion of primary production in biomass belowground biomass. ^[14] This belowground biomass can form deposits up to 8m deep. ^[14] Marshes Provide valuable habitat for plants, birds, and juvenile fish, protect coastal habitat from storm surge and flooding, and can Reduce nutrient loading to coastal waters. ^[15]Similarly to mangrove and seagrass habitats, marshes also serve as important carbon sinks . ^[16] Marshes sequester C in the underground biomass of organic sedimentation and anaerobic -dominated decomposition. ^[16] Salt marshes cover approximately 22,000 to 400,000 km ² globally, with an estimated carbon burial rate of 210 g C m ^-2yr ^-1 . ^[14] Tidal marshes have been impacted by humans for centuries, including modification for grazing, haymaking, reclamation for agriculture, development and ports, evaporation ponds for salt production, modification for aquaculture, insect control, tidal power and flood protection. ^[17] Marshes are also susceptible to oil pollution, industrial chemicals, and most commonly, eutrophication . Introduced species, sea-level rise, river damming and decreased sedimentation are additional long-term effects that affect marsh habitat, and in turn, may affect carbon sequestration potential. ^[18]

Algae

Both macroalgae and microalgae are being investigated as possible means of carbon sequestration . ^{[19] [20] [21] [22]} Because algae Lack the complex lignin associated with terrestrial plants , the carbon in algae is released into the atmosphere more than Rapidly carbon is captured land. ^[21] [23] Algae have been proposed as a short-term storage of carbon that can be used as a feedstock for the production of various biogenic fuels. Microalgae are often put to a potential feedstock for carbon-neutral biodieseland biomethane production due to their high lipid content. ^[19] Macroalgae, on the other hand, do not have high lipid content and have limited potential biodiesel feedstock, although they can still be used as feedstock for other biofuel generation. ^[21] Macroalgae have also been investigated as a feedstock for the production of biochar . The biochar produced from macroalgae is higher in agriculturally important nutrients than biochar produced from terrestrial sources. ^[22]Another novel approach to carbon capture which utilizes algae is the Bicarbonate-based Integrated Carbon Capture and Algae Production Systems (BICCAPS) developed by a collaboration between Washington State University in the United States and Dalian Ocean University in China. Many cyanobacteria , microalgae, and macroalgae species can utilize carbonate as a carbon source for photosynthesis . In the BICCAPS, alkaliphilic microalgae utilizes carbon captured from flue gases in the form of bicarbonate . ^[24] [25] In South Korea, macroalgae has been used as a part of a climate change mitigation program. The country has established the Coastal CO ₂Removal Belt (CCRB) which is composed of artificial and natural ecosystems. The goal is to capture carbon using large areas of kelp forest . ^[26]

Ecosystem restoration

Restoration of mangrove forests, seagrass meadows, marshes, and kelp forests has been implemented in many countries. ^[27] [28] These restored ecosystems have the potential to act as carbon sinks. Restored seagrass meadows were found to start sequestering carbon in sediment within four years. This was the time needed to reach a sufficient depth of sediment deposit. ^[28] Similarly, mangrove plantations in China showed higher levels of sedimentation than mangrove forests. This pattern in sedimentation rate is thought to be a function of the plantation’s young age and lower vegetation density. ^[27]

Nutrient stoichiometry of seagrasses

The primary nutrients in the determination of carbon (C), nitrogen (N), phosphorus (P), and light for photosynthesis. Nitrogen and Phosphorus can be obtained from the sediment of the water column and can be used in both ammonium (NH ⁴⁺ ) and nitrate (NO ³ ) form. ^[21]

A number of studies from around the world are of wide range in the concentrations of C, N, and P in seagrasses depending on their species and environmental factors. For instance, plants collected from high-nutrient environments had lower C: N and C: P ratios than plants collected from low-nutrient environments. Sea grass stoichiometry does not follow the Redfield ratio commonly used as an indicator of nutrient availability for phytoplankton growth. In fact, a number of studies in the world have found that the proportion of C: N: P in seafood can vary widely depending on their species, nutrient availability, or other environmental factors. Depending on environmental conditions, sea grasses can be either P-limited or N-limited. ^[29]

An early study of sea grass stoichiometry suggests that the ” redfield ” balance ratio between N and P for fat is approximately 30: 1. ^[23] However, N and P concentrations are strictly not correlated, suggesting that fatty acids can be adapted to their nutrient uptake based on what is available in the environment. For example, seafood fat meadows have been shown to be higher in the diet. Alternately, sea fat in environments with Higher loading rates and organic matter diagenesis supply more P, leading to N-limitation. The testudinum is the limiting nutrient. The nutrient distribution in T. testudinumranges from 29.4-43.3% C, 0.88-3.96% N, and 0.048-0.243%. This equates to a mean ratio of 24.6 C: N, 937.4 C: P, and 40.2 N: P. This information can be used to characterize the nutrient availability of a fish (which is difficult to measure directly) by sampling the sea fat living there. ^[18]

It is another factor that can affect the nutrient stoichiometry of fat. Nutrient limitation can only occur when photosynthetic energy causes fat to grow faster than the influx of new nutrients. For example, low light environments tend to have a lower C: N ratio. ^[18] Alternately, high-N environments can have an indirect negative effect on seagrass growth by promoting growth of algae that reduces the total amount of available light. ^[14]

Nutrient variability in sea grasses can have potential implications for wastewater management in coastal environments. High water equivalent of anthropogenic nitrogen discharge causes eutrophication Could Previously in N-limited environments, leading to hypoxic condition in the sea grass meadow and Affecting the carrying capacity of That ecosystem. ^[18]

A study of annual deposition of C, N, and P from P. Oceanica seagrass meadows in northeast Spain found that the meadow sequestered 198 g C m-2 yr-1, 13.4 g N m-2 yr-1, and 2.01 g P m-2 yr-1 into the sediment. Subsequent remineralization of carbon from the sediments due to respiration of approximately 8% of the sequestered carbon, or 15.6 g C m-2 yr -1. ^[25]

Distribution and decline of blue carbon ecosystems

Seagrasses, mangroves and marshes are approximately 49 million hectares worldwide. ^[30] Seagrass ecosystems range from tropical to tropical regions, mangroves are found in tropical and sub-tropical ecosystems and tidal marshes are found in most parts of the United States. ^[30] As habitats are altered That sequester carbon and Decreased, Stored That amount of C being white is released into the atmosphere, continuing the current accelerated rate of climateexchange. These impacts would have been achieved in these habitats and would have been sequestered in these habitats. Declines of vegetated coastal habitats are seen worldwide; Examples of Mangrove Disease in Indonesia, while in Europe and in the United States. Quantifying rates of decreased carbon dioxide for the sake of ecotourism, which is estimated to be 30% higher than that of carbon dioxide, 30% -40% of tidal marshes and seagrasses and approximately 100% of mangroves could be gone in the next century. ^[30]

Decline in seagrasses, water quality issues, agricultural practices, invasive species, pathogens, fishing and climate change. ^[31] Over 35% of global mangrove habitat remains. Decreases in habitat, settlement for aquaculture, development, etc., overfishing, and climate change, according to the World Wildlife Fund . ^[32] Nearly 16% of mangroves assessed by the IUCN are on the IUCN Red List ; Due to development and other causes 1 in 6 worldwide mangroves are in threat of extinction. ^[33]Dams threatening habitats by slowing the reach of freshwater reaching mangroves. Coral reef destruction also plays a role in mangrove habitat health as reefs slow wave energy to a level that mangroves are more tolerant of. Salt marshes may not be expanding in relation to forests, but they have more than tropical rainforests. Rates of burial have been estimated at 87.2 ± 9.6 Tg C yr-1 which is greater than that of tropical rainforests, 53 ± 9.6 Tg C yr-1. ^[34]Since the 1800s salt marshes have been disturbed due to development and lack of understanding their importance. The consequences of increasing degraded marsh habitat are decreasing in sediment stock, decreasing in plant biomass and thus decreasing. in photosynthesis reducing the amount of CO2 taken up by the plants, failure of C in plant blades to be transferred into the sediment, possible acceleration of erosive processes due to lack of plant biomass, and acceleration of buried C release to the atmosphere. ^[34]

Reasons for decline of mangroves, seagrass, and marshes include climate change, climate change, climate change, climate change, and climate change. Increases in these activities C from sediments. As anthropogenic effects and climate change are Heightened, the effectiveness of blue carbon sinks will diminish and CO ₂ emission will be further Top Increased. Data on the rates at qui CO ₂ is released into the atmosphere being white is not robust Currently, research is being white HOWEVER Conducted has to gather better information to analyze trends. Loss of underground biomass (roots and rhizomes) will allow for CO₂ to be emitted changing these habitats into sources rather than carbon sinks. ^[34]

Sedimentation and blue carbon burial

Organic carbon is only available from the oceanic system if it reaches the sea floor and gets covered by a layer of sediment. Reduced oxygen levels in environments mean buried That tiny bacteria Who eat organic matter and breathes CO ₂ can not decompose the carbon, so it is removed from the system Permanently. That organic matter sinks goal is not buried by a Sufficiently deep layer of sediment is subject to resuspension by changing ocean currents, bioturbation by organisms That live in the top layer of marine sediments, and decomposition by heterotrophic bacteria. If any of these processes occur, the organic carbon is released back into the system. Carbon sequestrationIt takes place only when it is erosion, bioturbation, and decomposition. ^[14] [35]

Spatial variability in sedimentation

Sedimentation is the rate at which floating or suspended particulate matter sinks and accumulates on the ocean floor. The faster (more energetic) the current, the more sediment it can pick up. As sediment laden slow currents, the particles fall out of suspension and come to rest on the sea floor. In other words, a fast current can pick up lots of heavy grains. As can be imagined, different places in the ocean vary drastically when it comes to the amount of suspended sediment and rate of deposition. ^[35]

Open ocean

The open ocean HAS very low sedimentation rates Because MOST of the sediment That Make it here are the carried by the wind. Wind transport accounts for a small fraction of the total sediment delivery to the oceans. In addition, there is much less plant and animal life living in the open ocean that could be buried. Therefore, carbon burials are relatively slow in the open ocean. ^[36]

Coastal margins

Coastal margins have high sedimentation rates due to sediment input by rivers, which account for the vast majority of sediment delivery to the ocean. In most cases, sediments are deposited near the river or in the direction of the sea. In some places sediment falls into submarine canyons and is transported off-shelf, if the canyon is widely available. Coastal margins also contain various marine species, especially in places that experience periodic upwelling. More marine life combined with higher sedimentation rates on coastal margins creates hotspots for carbon burial. ^[14] [37]

Submarine Canyons

Marine canyons are magnets for sediment because they carry currents along the way, the path of the current crosses canyons perpendicularly. When the same amount of water is suddenly in the water and the sediment. Due to the extreme depositional environment , the Nazare Canyon near Portugal is 30 times greater than the adjacent continental slope ! This canyon alone accounts for about 0.03% of global terrestrial organic carbon burial in marine sediments. This may not seem like much, but the submarine canyon submarine only makes up 0.0001% of the area of ​​the worlds ocean floor. ^[36]

Human changes to global sedimentary systems

Humans have been changing sediment cycles on a massive scale.

Agriculture / land clearing

The first major change to global sedimentary cycling occurred when humans started clearing land to grow crops. In a natural ecosystem, roots of plants hold sediment in place when it rains. Trees and shrubs reduce the amount of rainfall that impacts the dirt, and create obstacles that forest streams must flow around. When all vegetation is removed from rainfall, there are no roots to the sediment, and there is nothing to stop the flow of rivers. Because of this, land clearing causes an increase in erosion rates when compared to a natural system.

Dams

The first damsdate back to 3000 BC and were built to control flood waters for agriculture. When sediment laden river flows to a reservoir, the water slows down as it pools. Since the beginning of the past, the water has been seduced by the water. The result is that they are almost 100% efficient sediment traps. Additionally, the use of dams for flood control reduces the ability of downstream channels to produce sediment. Since the vast majority of sedimentation occurs during the worst floods, the frequency and intensity of flood-like flows is drastically changing production rates. For thousands of years there have been significant impacts on global sedimentary cycles, except for local impacts that have been significant.hydroelectric power in the last century has caused an enormous boom in dam building. Currently only one of the world’s largest rivers for unimpeded to the ocean. ^[38]

Channelization

In a natural system, the banks of a river will meander back and forth as different channels eroded, accrete, open, close gold. Seasonal floods regularly flooded riverbanks and deposits nutrients on adjacent flood plains. These services are essential to natural ecosystems, but can be disturbed for humans, who love to build infrastructure and development close to rivers. In response, they are often channelized , meaning that their banks and sometimes beds are armed with a hard material, such as rocks or concrete, which prevents erosion and fixes the stream in place. This inhibits sedimentation because there is much less soft substrate left for the river to take downstream.

Impacts

Currently, the net effect of humans on global sedimentary cycling is a drastic reduction in the amount of sediment that makes it to the ocean. If we continue to build dams and channelize rivers, we will continue to look at coastal areas, sinking deltas, shrinking beaches, and disappearing salt marshes. In addition, it is possible that we could ruin the influence of coastal margins to bury blue carbon. Without sequestration of carbon in coastal marine sediments, we will be able to accelerate global climate change. ^[39]

Other influencing factors blue carbon burial rates

Density of vegetation

The density of vegetation in mangrove forests, seagrass meadows, and tidal marshes is an important factor in carbon burial rates. The density of the vegetation must be sufficient to change water flows to reduce erosion and increase sediment deposition. ^[40]

Nutrient load

Increases in carbon capture and sequestration have been observed in both mangrove and seagrass ecosystems, which have been submitted to high nutrient loads. ^[20] Intentional fertilization has been used in seagrass meadow restoration. Perches for seabirds are located in the meadow and the bird droppings are the source fertilizer. The fertilization allows fast growing varieties of seagrasses to establish and grow. The species composition of these meadows is markedly different from the original seagrass meadow, although after the meadow has been reestablished and fertilization terminated, the meadows return to a species composition that closely approximates an undisturbed meadow. ^[41]Research done on mangrove soils from the Red Sea has shown that increases in nutrient loadings and increases carbon mineralization and subsequent CO ₂ release. ^[42] This neutral effect of fertilization was found in all mangrove forest types. Carbon capture rates also increased in these forests due to increased growth rates of mangroves. In forests with increases in respiration there were also increases in mangrove growth of up to six times the normal rate. ^[23]

Engineered Approaches to Blue Carbon

A US Department of Energy study from 2001 Proposed to replicate a natural process of carbon sequestration in the ocean by-combining water rich in CO ₂ gas with carbonate [CO –
3 ] to Produce has bicarbonate [HCO –
3 ] slurry. Practically, the engineered process could involve hydrating the CO ₂ from power plant flue gas and running through a bed of limestone to ‘fix’ the carbon in a saturated bicarbonate solution. This solution could be deposited at sea in the deep ocean. The cost of this process, from $ 90 to $ 180 per tonne of CO₂ and Was highly dependent on the distance required to transporting limestone, seawater, and the resulting and bicarbonate solution.

Expected benefits from bicarbonate direct production CO ₂ gas injection would be a much smaller change in ocean acidity and a longer period of time for the future. ^[43]

References