Blue Carbon
Blue carbon is the carbon stored in coastal or ocean ecosystems, such as mangroves, seagrass meadows, tidal marshes, and shellfish reefs. Carbon is stored in plant biomass and the associated soils and sediments of these ecosystems.
Introduction
Blue carbon is an important player in the fight against climate change beyond its carbon storing potential. Both coastal and ocean ecosystems full of plants like mangrove trees or kelp have other majorly important climate adaptation and mitigation potentials, giving them dual importance beyond their carbon sequestration and storage.
These solutions can and must be scaled consciously and sustainably with ocean ecosystems, biodiversity, and species in mind.
Main components
Brief descriptions of the three main components of blue carbon are provided below:
Mangroves
Mangroves are a group of 80+ species of trees and shrubs that grow in coastal intertidal zones around the tropics and subtropics. They are recognizable by their distinctive prop roots, which make the trees appear like they are standing on stilts above the water. These roots slow the movement of water which allows sediments to settle and accumulate, building up low-oxygen soils beneath them.
Seagrass Meadows
Seagrasses can be found underwater in shallow coastal areas and in the brackish waters of estuaries (where rivers meet the sea). They generally grow in large groups to make up ‘meadows’ or ‘beds’. Like their terrestrial counterparts, seagrasses have stems, with long green leaves, produce pollen and seeds, and have roots that anchor them to the seafloor sand and help stabilize sediments.
Tidal Marshes
Tidal marshes are wetlands found near estuaries and coasts that flood and drain as tides come in and then recede. Salt-tolerant plants (e.g., some herb, grass, and low shrub species) grow in these ecosystems and create dense strands which trap and stabilize the sediments transported in on the tides. Contrary to mangroves, tidal marshes occur predominantly in temperate regions and at high latitudes.
How it works
Photosynthesis
The sequestration of carbon by coastal plants, both above and below water, is facilitated by photosynthesis.
First, the plants absorb CO₂ from their surrounding environment, be it the atmosphere or water. Then, using energy from the sun, pigments, such as chlorophyll convert water and CO₂ to oxygen and glucose.
The life-sustaining oxygen is released from the plants, and the glucose goes on to build up carbon-rich biomass.
Coastal Carbon Storage
Carbon is intermediately stored in plant and animal biomass, however, only carbon stored in marine soils and sediments is considered securely stored on a long-term basis.
Carbon is introduced into these soils and sediments via roots while the plants are still growing, and when carbon-rich necromass is incorporated after the plants die. As coastal ecosystems are water-logged, there is little oxygen to facilitate necromass breakdown. Therefore, the carbon remains safely stored, sometimes on the millennial timescale.
Food and Shelter Provision
The restoration of coastal ecosystems is an integral part of enhancing biodiversity. Compared to the area they take up, mangroves, seagrass meadows, and tidal marshes provide a disproportionate amount of services to land, water and air based animals. For example, mangroves and seagrass meadows act as the nurseries and teaching grounds for the majority of the world’s commercially caught fish, making them vitally important for human food security too. Monkeys, mollusks, tigers, turtles, crabs, clams, shrimp, sharks, bacteria, barnacles, and hundreds of species of birds and amphibians (to name just a few) all rely on these habitats for food and protection.
An important player in the fight against climate change
Blue Carbon is by no means a solution in and of itself to climate change. In fact, the projected CO₂ removal by CBC projects is only a small fraction of global GHG emissions. However, the restoration of mangroves, seagrasses, and tidal marshes will all contribute to the death by 1000 cuts of climate change.
When used in harmony with a suite of other CO₂ removal methods blue carbon will have an important impact. Taking into consideration the accompanying invaluable societal and environmental benefits these projects also supply, this method is a no-brainer.
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Blue carbon ecosystems are present on every continent, except for Antarctica. Despite only covering <2% of total ocean area, they account for ca. 50% of the carbon sequestered in ocean sediments.
These sediments can store up to 1,000 tC ha-1, much higher than their terrestrial soil counterparts. Therefore, restoring these ecosystems represents an efficient and effective way to drawdown CO₂, with research indicating that an additional 0.2-0.85 Gt CO2e y-1 removal is achievable between now and 2050.
Moreover, as very little decomposition is possible in such anoxic conditions, the permanence of blue carbon performs favourably compared to terrestrial nature-based CO₂ removal solutions.
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Alongside the aforementioned biodiversity, blue carbon provides many more ecosystem services. These services are especially important for the most vulnerable communities living along coastlines (40% of the world’s population lives within 100km of a coast). Mangroves, seagrasses, and tidal marshes can all protect infrastructure from storm surges, tsunamis and flooding, preventing billions of dollars of damages.
They do this while filtering water, ensuring clean and pristine coastal waters. Additionally, coastal ecosystems possess a traditional significance to many communities, and so their restoration would rehabilitate some of their cultural and spiritual integrity, while also providing a way to diversify their incomes.
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