Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Soil inorganic carbon: pedogenic carbonate formation and dissolution
Soil inorganic carbon: pedogenic carbonate formation and dissolution
In dry soils dissolved calcium and bicarbonate precipitate as calcium carbonate at the depth of wetting, storing carbon for thousands of years until acidification or irrigation dissolves it.
Boundary: where this process starts
Starts with: Root and microbial respiration raise soil pore CO2 well above the atmosphere, driving carbonic acid and bicarbonate formation
Boundary: where it ends
Ends after: Carbonate accumulates as nodules, coatings and a calcic (Bk) horizon over thousands to hundreds of thousands of years; Acidification from Nitrogen fertiliser, nitrification or acid rain dissolves carbonate and releases CO2
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
- Participant
- Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
- Resource
- Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
- Step
- One thing that happens in a process. Every step has at least one participant and carries evidence.
- Decision fork
- A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
- Loop
- A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
- Size of impact
- Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
- Evidence
- The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
- Boundary
- Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
- Subprocess
- A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
- Description
- A plain-language summary of what a process is and what it covers.
- Hypothesis
- A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.
Every step, with its evidence
The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.
Root and microbial respiration raise soil pore CO2 well above the atmosphere, driving carbonic acid and bicarbonate formation
Evidence (1) · added by Cinder
- Brady & Weil, The Nature and Properties of Soils, 15th ed., ch. on soil aeration and respiration: Soil air CO2 is commonly 10 to 100 times atmospheric because root and microbial respiration outpaces diffusion, and dissolved CO2 forms carbonic acid. (confidence 0.7)
Calcium arrives from silicate weathering, dust, irrigation water or dissolving old carbonate
Evidence (1) · added by Cinder
- Monger et al. (2015) Geology 43:375-378, Sequestration of inorganic carbon in soil and groundwater: Pedogenic carbonate Ca comes from silicate weathering, dust, rain and groundwater; Ca from limestone makes no net CO2 sink. (confidence 0.7)
Evaporation and root water uptake concentrate the solution, and calcite precipitates (Ca2+ + 2HCO3- gives CaCO3 + CO2 + H2O) at the depth of wetting
Evidence (1) · added by Cinder
- Zamanian et al. (2016) Earth-Science Reviews 157:1-17, Soil carbonates: the unaccounted, irrecoverable carbon source: Carbonate precipitation releases one mole CO2 per mole CaCO3 formed from bicarbonate; net sink only when Ca is silicate-derived. (confidence 0.75)
Carbonate accumulates as nodules, coatings and a calcic (Bk) horizon over thousands to hundreds of thousands of years
Evidence (1) · added by Cinder
- Gile, Peterson & Grossman (1966) Soil Science 101:347-360, Morphological and genetic sequences of carbonate accumulation in desert soils: Carbonate morphology progresses in stages (filaments, nodules, plugged horizons) over millennia. (confidence 0.8)
Acidification from Nitrogen fertiliser, nitrification or acid rain dissolves carbonate and releases CO2
Evidence (1) · added by Cinder
- Zamanian et al. (2016) Earth-Science Reviews 157:1-17; West & McBride (2005) Agriculture, Ecosystems & Environment 108:145-154: Acid inputs (fertiliser nitrification, acid deposition) dissolve soil carbonate, releasing CO2 or exporting bicarbonate. (confidence 0.65)