2 research outputs found
Rapid Removal of Atmospheric CO<sub>2</sub> by Urban Soils
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 CO<sub>2</sub>/ha (8.5 kg of CO<sub>2</sub> m<sup>–2</sup>) 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 CO<sub>2</sub> ultimately derived
from the atmosphere, precipitating as calcite. Stable isotope data
confirm an atmospheric origin for carbonate carbon, and <sup>14</sup>C 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 CO<sub>2</sub> from the atmosphere annually.
The maximal global potential is estimated to be approximately 700–1200
Mt of CO<sub>2</sub> 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
Black Carbon Contribution to Organic Carbon Stocks in Urban Soil
Soil holds 75% of
the total organic carbon (TOC) stock in terrestrial
ecosystems. This comprises ecosystem-derived organic carbon (OC) and
black carbon (BC), a recalcitrant product of the incomplete combustion
of fossil fuels and biomass. Urban topsoils are often enriched in
BC from historical emissions of soot and have high TOC concentrations,
but the contribution of BC to TOC throughout the urban soil profile,
at a regional scale is unknown. We sampled 55 urban soil profiles
across the North East of England, a region with a history of coal
burning and heavy industry. Through combined elemental and thermogravimetic
analyses, we found very large total soil OC stocks (31–65 kg
m<sup>–2</sup> to 1 m), exceeding typical values reported for
UK woodland soils. BC contributed 28–39% of the TOC stocks,
up to 23 kg C m<sup>–2</sup> to 1 m, and was affected by soil
texture. The proportional contribution of the BC-rich fraction to
TOC increased with soil depth, and was enriched in topsoil under trees
when compared to grassland. Our findings establish the importance
of urban ecosystems in storing large amounts of OC in soils and that
these soils also capture a large proportion of BC particulates emitted
within urban areas