Rapid Removal of Atmospheric CO₂by Urban Soils

Abstract

The measured calcium carbonate content of soils to a depth of 100 mm at a large urban development site has increased over 18 months at a rate that corresponds to the sequestration of 85 t of CO2/ha (8.5 kg of CO2 m(-2)) annually. This is a consequence of rapid weathering of calcium silicate and hydroxide minerals derived from the demolition of concrete structures, which releases Ca that combines with CO2 ultimately derived from the atmosphere, precipitating as calcite. Stable isotope data confirm an atmospheric origin for carbonate carbon, and 14C dating indicates the predominance of modern carbon in the pedogenic calcite. Trial pits show that carbonation extends to depths of ≥1 m. Work at other sites shows that the occurrence of pedogenic carbonates is widespread in artificially created urban soils containing Ca and Mg silicate minerals. Appropriate management of fewer than 12000 ha of urban land to maximize calcite precipitation has the potential to remove 1 million t of CO2 from the atmosphere annually. The maximal global potential is estimated to be approximately 700-1200 Mt of CO2 per year (representing 2.0-3.7% of total emissions from fossil fuel combustion) based on current rates of production of industry-derived Ca- and Mg-bearing materials.

Assessing ocean alkalinity for carbon sequestration

“…Notionally, the products of dissolution (including increased alkalinity of rainwater) are transported to the ocean via runoff, rivers, and shallow groundwater. Alternatively, Manning [] and Manning et al [] suggest that solution chemistry in soil pore waters may promote the precipitation of carbonate minerals, which has been demonstrated widely in anthropogenic soils [ Renforth et al , ; Washbourne et al , , ]. If so, the precipitated carbonate becomes the sink for CO 2 rather than ocean alkalinity.…”

Surface Soil Carbon Storage in Urban Green Spaces in Three Major South Korean Cities

“…We investigated total soil C in the roadside, park, school forest, and riverside, following the legal classification of UGS's as defined by the National Urban Forest Inventory [27] and the Environmental Geographic Information Service (http://egis.me.go.kr) (full details in the footnotes of Table 1). Because the inorganic C produced by carbonation reactions in calcareous materials (e.g., concrete, cement, parent material) can form a fraction of soil C, in the present study, in addition to organic C [12][13][14]28], we focused on total C, covering both organic and inorganic C. The UGS's exclude remnant, non-urbanized, and mountainous forest areas, such as green belt and conservation areas in the city districts (as defined by the administrative system of Korea). The four UGS types represent approximately 90% of all the UGS areas in South Korea.…”

“…Soils support various ecosystem services such as nutrient cycling, habitat provision, food production, storm water management, and carbon (C) storage [3][4][5][6]. Here, the emphasis on the conservation or sequestration of soil C, with a C stock greater than that of atmosphere and biomass combined [7][8][9][10][11], is extended to urban soil C, both organic and inorganic C [12][13][14]. The significance of UGS's for terrestrial C inventories and the need to treat them distinctly from other major land types (e.g., forest, agricultural land, grassland, and wetland) is underscored by its special treatment as a separate land category, settlements, which encompasses all developed land according to the Good Practice Guidance (GPG) and Guidelines (GL) of the Intergovernmental Panel on Climate Change (IPCC) [15,16].…”

Sequestration of atmospheric carbon dioxide as inorganic carbon in the unsaturated zone under semi-arid forests

“…A net sequestration of atmospheric CO2 therefore unambiguously occurs (Kolosz et al, 2016;Kolosz et al, 2017;Hartmann et al, 2017;Washbourne et al, 2015). A variety of sources of calcium ions, outside silicate weathering or from relict limestone, are present in nature.…”