Biosequestration is a natural, biological process that captures and stores atmospheric carbon dioxide (\(CO_2\)) in living organisms and ecosystems. This process uses natural systems, such as plants and soil, to draw down and hold carbon that would otherwise contribute to rising greenhouse gas concentrations. Biosequestration is an important climate change mitigation strategy, enhancing nature’s capacity to remove excess carbon from the air and help rebalance the carbon cycle.
The Underlying Biological Process
The foundation of biosequestration is photosynthesis, carried out by plants, algae, and certain bacteria. During photosynthesis, these organisms absorb atmospheric \(CO_2\) and use sunlight to convert it into sugars and other organic compounds, transforming gaseous carbon into solid biomass. This conversion integrates carbon atoms into the plant’s structure, including its leaves, stems, and roots.
The carbon cycle involves both short-term and long-term storage mechanisms within the biosphere. Short-term storage occurs while carbon remains in living plant tissue. A portion of this carbon is pumped into the soil through root exudates and the decomposition of dead plant material. Microbes, such as fungi and bacteria, break down this organic matter and stabilize it into complex, long-lasting soil organic carbon (SOC) compounds, ensuring the carbon is locked away.
Major Biosequestration Reservoirs
Carbon is stored across major global reservoirs, categorized into terrestrial and aquatic systems. Terrestrial reservoirs include forests and soils, which hold immense quantities of sequestered carbon. Forests serve as carbon sinks by storing carbon in above-ground biomass (trunks, branches, and leaves) and in below-ground root systems.
Soil represents one of the largest terrestrial pools of organic carbon globally, often holding more carbon than all the world’s vegetation and the atmosphere combined. This carbon is primarily held as soil organic matter, which increases soil fertility and water retention. Aquatic biosequestration occurs in marine and freshwater environments, notably through phytoplankton, which perform photosynthesis and form the base of the ocean’s biological carbon pump.
Coastal ecosystems, collectively known as “blue carbon,” are highly effective at carbon storage. These include tidal marshes, seagrass meadows, and mangrove forests. The waterlogged, anaerobic conditions in the sediments of these ecosystems significantly slow the decomposition of organic material. This lack of oxygen causes carbon-rich matter to accumulate and be stored for millennia at rates often greater than those found in terrestrial forests.
Strategies for Enhanced Sequestration
Human intervention can boost the natural rates of biosequestration through targeted management practices. A direct method is afforestation, which involves planting new forests on land that has not historically been forested, and reforestation, which restores trees to recently cleared land. These practices increase the total global volume of woody biomass, providing a long-term carbon sink. Sustainable forest management also promotes enhanced sequestration by managing tree density and promoting the growth of large, long-lived trees.
In agriculture, strategies focus on increasing soil organic carbon levels, often grouped under regenerative agriculture. Practices like no-till farming minimize soil disturbance, preventing the rapid oxidation of organic matter that releases \(CO_2\) back into the air. The use of cover crops, such as clover and cereal rye, keeps the soil covered year-round, increasing root biomass and continuously adding fresh organic material.
Other effective farming techniques include diversified crop rotations and the integration of agroforestry, which introduces trees and shrubs into agricultural landscapes. These methods not only sequester carbon but also improve soil health, water retention, and crop resilience. Restoration of coastal habitats, such as replanting mangrove forests and salt marshes, also serves as an enhanced biosequestration strategy, capitalizing on the high carbon storage capacity of these blue carbon ecosystems.
Duration and Verification of Carbon Storage
A primary concern with biosequestration is the stability, or permanence, of the stored carbon, as biological sinks are considered volatile compared to geological storage. Carbon stored in biomass and soil is vulnerable to reversal, meaning it can be released back into the atmosphere through natural or human-caused disturbances. For instance, events like wildfires, disease outbreaks, or deforestation can rapidly turn a carbon sink into a carbon source.
The duration of storage is highly dependent on the ecosystem and management practices, ranging from decades to thousands of years in stable soil or wetland sediments. To ensure that sequestration efforts deliver reliable climate benefits, rigorous monitoring, reporting, and verification (MRV) protocols are necessary. Verification relies on a combination of techniques, including remote sensing via satellites to track changes in vegetation cover and biomass, and precise soil sampling to measure increases in organic carbon content.