Critical load calculations do not include a time perspective, i. e. they do not say
anything about when the effects will occur (Figure 2). There is a time lag between
exceeding of the critical load and violating of the critical limit. This is due to the
ion exchange processes where hydrogen ions exchange with base cations on the soil
particles, a process which leads to a maintained base cation concentration in the soil
solution until the soil particles are depleted of base cations, i. e. the base saturation
is low. The time lag depends on the base saturation of the soil and differs among
sites. It can be modeled by dynamic models such as the SAFE model (Warfvinge
and Sverdrup, 1992).