Critical Loads, Target Load Functions and Dynamic Modelling for Surface Waters and ICP Waters Sites (ICP Waters report 83/2006)

Critical load functions (CLF) for ICP Water sites estimated with the FAB model and based on recent data (2000-02) do not differ greatly from those based on earlier data (1992-94/5). The ICP Waters sites in Europe are largely characteristic of the most sensitive waters within the EMEP 50 km grid cell. Target load functions (TLF) require use of a dynamic model. For acidified waters the TLF for sulphur (Smax) is often lower than the CLF, because of time lags in the recovery of catchment soils in response to reduced S deposition. On the other hand the TLF for nitrogen (Nmax) is often higher than the CLF, because most catchments presently are not N-saturated and retain a large fraction of N-deposition. Scientific understanding of processes governing N-retention and loss from catchments remains insufficient and is the major source of uncertainty in modelling acidification of soils and waters. Climate change will also affect the uncertainty with respect to N