The water table splits the 60 cm peat column into an oxic (aerobic) zone above it and an anoxic (anaerobic) zone below. Decomposition in each zone follows a Q10 temperature response; photosynthetic carbon uptake (NPP) peaks near an optimal, near-surface water table:
tempFactor = Q10^((T-10)/10), Q10 = 2.0
oxic_cm = waterTableDepth, anoxic_cm = 60 - waterTableDepth
R_aero = k_a · tempFactor · oxic_cm · quality (CO2, aerobic)
R_anaero = k_n · tempFactor · anoxic_cm · quality (organic C consumed, anaerobic)
CH4_produced = R_anaero · 0.35
CH4_oxidised = CH4_produced · clamp(oxic_cm/60 · 0.8, 0, 0.75) (passes back through oxic zone as CO2)
CH4_flux = CH4_produced - CH4_oxidised
NPP = NPPmax · veg% · moistureFactor(waterTable) · tempFactor_photo
NECB = NPP - R_aero - (R_anaero - CH4_produced + CH4_oxidised) - CH4_flux
A deep water table thickens the oxic zone: more CO2 escapes and more of the methane produced below gets oxidised on the way up, but photosynthesis also drops once the surface dries past its moisture optimum. A shallow (near-surface) water table does the opposite — the bog turns anaerobic, methane emission rises, but so does the Sphagnum growth that feeds it. NECB > 0 means the bog is a net carbon sink (peat accumulates); NECB < 0 means it is a net source.
- Grey bubbles — CO2 rising from the aerobic zone above the water line.
- Amber bubbles — CH4 rising from the anaerobic zone below the water line, partly re-absorbed (dimming) as they cross back through the oxic layer.
- Drought pulse — temporarily drops the water table, showing the aerobic-zone carbon-release spike this causes.