Understanding how and how much carbon dioxide can be fixed by natural ways Educational material mix for the School Agenda 21, compiled and adapted by Josean Kijera – Ingurugela, Donostia (Basque Country) 1 1. Carbon sink A carbon sink is a natural or artificial reservoir that accumulates and stores some carbon- containing chemical compound for an undefined time. The process by which carbon sinks remove carbon dioxide (CO2) from the atmosphere is known as carbon sequestration. Awareness of the significance of CO2 sinks has grown since the Kyoto Protocol, where their use as a form of carbon offset is promoted. There are different strategies used to enhance this generic process. Figure 1. Natural and anthropogenic interactions in the Earth´s carbon cycle (Source: The New York State Department of Environmental Conservation, DEC; http://www.dec.ny.gov/energy/76572.html) 2 2. Biosequestration Biosequestration is the capture and storage of the atmospheric greenhouse gas carbon dioxide by biological processes. This can happen by increasing photosynthesis (through some practices like preventing deforestation, reforestation and genetic engineering); by enhanced soil carbon trapping in agriculture; or by the use of algal biosequestration (algae bioreactor) to absorb CO2 emissions from coal, petroleum (oil) or natural gas based electricity generation, transportation... Biosequestration, as a natural process, has occurred in the past, and was responsible for the formation of the extensive coal and oil deposits which are now being Figure 2. Biosequestration of carbon, as CO2 by photosynthesis (Source: International burned for energy. Center for Tropical Agriculture, CIAT; http://dapa.ciat.cgiar.org/carbon- sequestration-one-true-green-revolution/) 3 Biosequestration of carbon by plants Some definitions: • Carbon dioxide: it is a by-product of respiration and substrate for the photosynthetic process; also, a greenhouse gas massively produced by hydrocarbon combustion. • CO2 flux: the transfer of a quantity of CO2 per unit of area and per unit of time. • Gross Primary Production (GPP): the total amount of organic material assimilated by plants in an assumed time. • Net Primary Production (NPP): the total amount of organic material accumulated by plants in a specified time; in other terms: NPP = Photosynthesis – Respiration. Carbon biosequestration in plants is the process by which CO2 is removed from the atmosphere and stored as plant biomass. 4 Carbon biosequestration can be considered at a number of levels. At the level of an discrete plant, the amount of carbon sequestered is this: CO2 sequestered = Photosynthesis – Respiration So that, the amount of sequestered carbon is just as to the NPP of the plant. If carbon biosequestration is considered at ecosystem level, some more factors have to be accounted. The diagram indicates the mean processes involved in ecosystem carbon sequestration: - Blue arrow: process that bring carbon into the ecosystem. - Red arrows: processes returning carbon from the ecosystem to the atmosphere. Figure 3. Carbon biosequestration in ecosystems by plants (Source: University of Colorado; http://www.colorado.edu/geography/blanken/GEOG%206181%20F all%202003/zarter/html/zarter_cseq.shtml) 5 Temperate forest and their capacity incorporating carbon dioxide Temperate forest, vegetation type with a more or less continuous canopy of broad-leaved trees. Such forests occur between approximately 25° and 50° latitude in both N and S hemispheres. Near the polar regions they grade into boreal forests, which are dominated by perennial conifers. Mixed forests, containing both deciduous and coniferous trees, occupy transitional areas. Temperate forests can be classified into two main groups: deciduous and evergreen. Figure 4. Temperate forest areas in the world (Source: Encliclopaedia Britannica; http://global.britannica.com/E Bchecked/topic/586555/tem perate-forest) 6 Deciduous forests are found in regions of the Northern Hemisphere that have moist, warm summers and frosty winters (primarily eastern North America, eastern Asia, and western Europe). In contrast, evergreen forests grow in areas with mild, nearly frost-free winters. They fall into two subcategories: - Broad-leaved forests. - Sclerophyllous forests. (Sclerophyllous vegetation has small, hard, thick leaves). The former grow in regions that have high year-round rainfall; the latter occur in areas with lower and more inconsistent rainfall. Figure 5 and 6. Temperate forest plants (Source: Encliclopaedia Britannica; http://global.britannica.com/EBchecked/topic/586555/temperate-forest) 7 Temperate forests are vigorous carbon sinks and deforestation in temperate zones has largely stopped. Where demand for land and/or water allows, reforestation would enable carbon sequestration and could provide other benefits, as well as higher biodiversity. Figure 7. Carbon contained in natural ecosystems (Source: Grida; http://www.grida.no/publications/rr/natural- fix/page/3725.aspx) 8 Terrestrial storage in wild lands and agricultural landscapes Soils exemplify a small to long-term carbon storage medium, and contain more carbon than all terrestrial vegetation and the atmosphere combined. Plant litter, like other biomass, accumulates as organic matter in soils, and is degraded by chemical weathering and biological degradation. More recalcitrant organic carbon polymers, such as cellulose, hemi- cellulose, lignin, aliphatic compounds, waxes and terpenoids, are collectively retained in the humus. Figure 8. Terrestrial storage of carbon in soils (Source: Big Sky Carbon; http://www.bigskyco2.org/whatisit/ter restrial) 9 Regenerative agriculture Current agricultural practices lead to carbon loss from soils. It has been suggested that improved farming practices could return the soils to being a carbon sink. Present wide- reaching practices of overgrazing are greatly reducing many grasslands' performance as carbon sinks. Some studies shows that regenerative agriculture could sequester up to 40 % of current CO2 emissions. So that, agricultural carbon sequestration has the potential to mitigate global warming. When using biologically based regenerative practices, this powerful advantage can be accomplished with no reduction in yields or farmer profits. Organically managed soils can convert carbon dioxide from a greenhouse gas into a food- producing asset. Figure 9. Regenerative agriculture. Figure 10. Agriculture and sustainability. 10 Enhancing natural sequestration in forest Forests are carbon stores, and they are carbon dioxide sinks when they are increasing in density or area. For example, in Canada's boreal forests around the 80 % of the total carbon is stored in the soils like deceased organic matter. An important and large in time study about African, Asian, and South American tropical forests shows that tropical forests absorb about 18 % of all CO2 from by fossil fuels. Tropical reforestation is a good practice mitigating global warming until all available land has been reforested with mature forests. Truly mature tropical forests sequester no net carbon. In the equilibrium state, growth equals decay; in this situation, tropical soils do not accumulate humus as temperate forests do. Figure 11. Temperate forest of Montenegro. (Source: Wikipedia, Old-growth forest; http://en.wikipedia.org/wiki/Old- growth_forest) 11 The IPCC concluded that: A sustainable forest management strategy aimed at maintaining or increasing forest carbon stocks, while producing an annual sustained yield of timber fiber or energy from the forest, will generate the largest sustained mitigation benefit. Sustainable management practices promotes forests growing at a higher rate over a potentially longer period of time, providing net sequestration benefits in addition to those of unmanaged forests. Global Potential for Carbon Sequestration (Source: Wikispaces, Climate Change; http://climatechange.wikispaces.com /Carbon+Sequestering) 12 Life expectancy of forests varies throughout the world, influenced by tree species, site conditions and natural disturbance patterns. In some forests, carbon may be stored for centuries, while in other forests carbon is released with frequent stand replacing fires. Figure 12. Timber, and Figure 13. forest in fired (Source: Wikipedia, Wildfire; http://en.wikipedia.org/wiki/Wildfire) Forests that are harvested prior to stand replacing events allow for the retention of carbon in manufactured forest products such as lumber. However, only a portion of the carbon removed from logged forests ends up as durable goods and buildings. The remainder ends up as sawmill by-products such as pulp, paper and pallets, which often end with incineration (resulting in carbon release into the atmosphere) at the end of their lifecycle. 13 Biosequestration by reforestation Sequestration of CO2 trough reforestation is the replanting of trees, often on marginal crop and pasture lands, to incorporate carbon from atmospheric CO2 into biomass. For a good practice, previously retained carbon must not return to the atmosphere from burning or rotting when the trees die. To this end, the trees must grow in perpetuity or the wood from them must itself be sequestered, e.g., via biochar, bio-energy with carbon storage (BECS) or landfill. Short of growth in perpetuity, however, reforestation with long-lived trees (>100 years) will sequester carbon for a more graduated release, minimizing impact during the expected carbon crisis of the 21st century. Figure 14. Biosequestration by reforestation. Reforested land. IDEASGALORE: