Figure 2
Schematic representation of the developed mass balance model. For each box (representing the different soil layers), input fluxes (Ik,t) are rainfall (Rt) and litterfall (Lt) for the upper soil layer and, for the other layers, vertical transfer flux, mainly drainage, (Dk,t) from the overlying layer. Outputs (Ok,t) are vertical transfer (Dk,t) and root absorption (Ak,t) from the soil layer considered. Gas fluxes of Cl and 36Cl are neglected. At each time step, a fraction (Xk) of the Cl and 36Cl input fluxes is retained in the soil layer k building the Cl and 36Cl stock (Sk,t) while the remaining (1-Xk) is lost from the soil by drainage. A fraction (Zk) of Sk,t is released in the soil solution and also drained. An annual time step (t) is used to smooth seasonal variations. For each soil layer k, Sk,t is calculated. The equations of the model are presented in “Methods” section. Colours for the different soil boxes represent the different soil layers. No humus layer is considered, as the residence time for Cl in the type of humus encountered in the studied site is less than a year, the time step of the model (see “Methods” section for further information).
