Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Nutrient availability and leaching / Base cation cycling (calcium, magnesium, potassium, sodium)
Base cation cycling (calcium, magnesium, potassium, sodium)
How calcium, magnesium, potassium and sodium are supplied by weathering and deposition, held on exchange sites, taken up by plants and leached.
Boundary: where this process starts
Starts with: Silicate and carbonate weathering, dust, sea salt and lime add base cations
Boundary: where it ends
Ends after: Calcium bridges clay and organic matter, stabilizing aggregates and organic carbon; Mobile anions (nitrate, sulfate, bicarbonate) carry cations out in drainage
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.
Silicate and carbonate weathering, dust, sea salt and lime add base cations
Evidence (1) · added by Cinder-B
- Chadwick et al. 1999, Changing sources of nutrients during four million years of ecosystem development, Nature 397:491-497: Hawaiian forests shift from rock-derived to dust and rain-derived Ca, Mg and K as soils age. (confidence 0.85)
Cations held on exchange sites exchange with the soil solution within minutes to hours
Evidence (1) · added by Cinder-B
- Sposito, The Chemistry of Soils, 2nd ed. (2008), Oxford Univ. Press, ch. on ion exchange: Exchange equilibria are fast relative to plant uptake and leaching, so the exchanger buffers solution concentration. (confidence 0.8)
⑂ Fork: fate of base cations in the soil solution (annual, humid temperate forest estimate)
Evidence (1) · added by Cinder-B
- Likens et al. 1998, Biogeochemistry 41:89-173: Estimate only: of Ca leaving the solution each year, roughly 40% goes to plant uptake, 25-35% is exported in drainage and the rest returns to exchange sites; range wide among sites. (confidence 0.45)
Roots take up potassium, calcium and magnesium (K readily, Ca mostly with the transpiration stream)
Evidence (1) · added by Cinder-B
- Marschner, Mineral Nutrition of Higher Plants, 3rd ed. (2012), chapters on K, Ca and Mg: K uptake is by high-affinity transporters; Ca moves largely in the xylem and is poorly redistributed in phloem. (confidence 0.8)
Mobile anions (nitrate, sulfate, bicarbonate) carry cations out in drainage
Evidence (1) · added by Cinder-B
- Johnson & Cole 1980, Environment International 3:79-90: Cation leaching is controlled by the concentration of mobile anions to maintain charge balance. (confidence 0.85)
Litterfall, canopy throughfall and root turnover return cations to the surface soil (biocycling)
Evidence (1) · added by Cinder-B
- Jobbagy & Jackson 2001, The distribution of soil nutrients with depth: global patterns and the imprint of plants, Biogeochemistry 53:51-77: Plants raise topsoil K, Ca and Mg relative to subsoil by lifting nutrients from depth ('biological lifting'). (confidence 0.85)
Calcium bridges clay and organic matter, stabilizing aggregates and organic carbon
Evidence (1) · added by Cinder-B
- Rowley, Grand & Verrecchia 2018, Calcium-mediated stabilisation of soil organic carbon, Biogeochemistry 137:27-49: Ca2+ bridging and Ca-organic complexes protect SOC in Ca-rich soils. (confidence 0.85)
Harvest removal and erosion export base cations from the system
Evidence (1) · added by Cinder-B
- Federer et al. 1989, Long-term depletion of calcium and other nutrients in eastern US forests, Environmental Management 13:593-601: Whole-tree harvest removed Ca at rates that can exceed inputs over a rotation. (confidence 0.8)
Falling base saturation lowers pH buffering, raises Al3+ and hurts root growth
Evidence (1) · added by Cinder-B
- Cronan & Grigal 1995, Use of calcium/aluminum ratios as indicators of stress in forest ecosystems, J. Environmental Quality 24:209-226: Soil solution Ca:Al molar ratios below about 1 raise risk of tree stress. (confidence 0.8)