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Resource: used or used up in processesCarbon dioxide
Appears in 77 processs and 166 steps. Everything below is linked: open a process to see it in context.
Top processes
Living soil system
8 stepsDecomposition
8 stepsSoil gas exchange and redox
7 stepsCarbon cycling
6 steps- Where does a unit of CO2 go?
- Terrestrial carbon uptake and release
- Ocean carbon exchange and burial
- and 3 more in this process
Show 71 more processes
Weathering
4 stepsBacteria and archaea
4 steps- Which substrate feeds methanogenesis (roughly two thirds acetate, one third H2 plus CO2 in moderate-temperature paddy and sediment; bogs shift toward H2/CO2)
- Acetoclastic methanogens (Methanosarcina, Methanosaeta) split Acetate into Methane and Carbon dioxide
- Hydrogenotrophic methanogens reduce Carbon dioxide with Hydrogen supplied by syntrophic fermenters (H2 must stay at a few Pa)
- and 1 more in this process
- Soil CO2 efflux reaches about 98 Pg C per year globally, far above fossil emissions of about 9 Pg C
- Warming speeds enzyme and respiration rates, with Q10 typically 1.5 to 3 and higher at low temperature
- Rewetting dry soil causes a CO2 and mineral N pulse within hours (Birch effect) from released osmolytes and exposed organic matter
- and 1 more in this process
Primary production
3 steps- Plant production exceeds decay and peat accumulates at about 20 g C per m2 per year (about 1 mm per year)
- Methanogens in saturated peat convert acetate and H2 plus CO2 to Methane; production rises steeply with temperature (activation energy about 0.96 eV)
- Drainage or drought lowers the water table, oxygen enters and peat respires CO2 (drained peatland about 0.3% of land, about 5% of human CO2-equivalent emissions)
- Root and microbial respiration raise soil pore CO2 well above the atmosphere, driving carbonic acid and bicarbonate formation
- Evaporation and root water uptake concentrate the solution, and calcite precipitates (Ca2+ + 2HCO3- gives CaCO3 + CO2 + H2O) at the depth of wetting
- Acidification from Nitrogen fertiliser, nitrification or acid rain dissolves carbonate and releases CO2
- Fick's law: gas flux = -Ds dC/dz, where Ds is the soil gas diffusion coefficient
- Respiration consumes O2 and produces CO2, so the steady-state CO2 excess scales with respiration divided by Ds: halving Ds doubles the excess
- Soil air at depth commonly holds 0.3-3% CO2, about 10 to 100 times atmospheric (0.04%)
- Lloyd-Taylor function: respiration proportional to exp[309/(T-227)] gives Q10 about 3.3 near 0-10 C, 2.3 near 10-20 C and 1.9 near 20-30 C
- Warming-driven soil carbon loss is estimated at about 55 Pg C by 2050 in the top metre
- Deeper summer thaw exposes frozen organic matter to decomposition, releasing CO2 and methane; 5-15% of permafrost carbon may be released by 2100 under high emissions
Biological processes
2 stepsOrganic matter decomposition
2 stepsOften found with
Water 45Soil microbes 44Oxygen 40Plants 27Plant roots 24Carbon 22Soil organic matter 20Sunlight 19Methane 17Fungi 17Atmosphere 16Nitrogen 16
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