Oxygen flows

Oxygen flows in the soil profile are treated slightly differently depending on which oxygen flux approach that is used. Oxygen consumption is a result of aerobic plant and microbial respiration in the soil:

                 (6.90)

where o_ratioC is the molar ratio between oxygen gas and carbon.

For the steady-state approach the flux of oxygen from one layer (or from the atmosphere) to the layer below, q_O2, is a function of oxygen consumption and oxygen flux in the lower layer:

                                                        (6.91)

The concentration of oxygen, O_O2Conc, in each layer is calculated as:

                                      (6.92)

where Δz in this case symbolises the distance from the middle depth of one layer (z) to the middle depth in the layer above (z-1). The oxygen concentration of the uppermost soil layer is calculated with the same equation by exchanging O_O2Conc(z-1) with the oxygen concentration of the atmosphere, O_O2ConcAtm, calculated as:

                                           (6.93)

where o_ratioair is the molar ratio of oxygen to air and ρ_a(T) is the air density temperature function calculated as:

                                                       (6.94)

where ρ_a is the density of air at 20°C.

In the dynamic approach oxygen, O_O2, is calculated explicitly as:

                                                       (6.95)

and the concentration of oxygen, O_O2Conc, is calculated as:

                                                            (6.96)

where Δz is the layer thickness.

The flux of oxygen is calculated as:

                                                 (6.97)

For the uppermost soil layer, this equation is modified into:

                                               (6.98)