General Approaches for Calculating Critical Loads

The possible impact of a certain load on soil and surface water quality can be estimated by determining  

One can see that both algorithms are similar, but steady-state approaches based on MFC values do not practically take into account either ecosystem characteristics or their geographic situation. Eurthermore, there are many known drawbacks of traditional approaches applying MFC (Bashkin et al, 1993 Van de Flassche et al, 1997). Since the steps in the steady-state approach are similar but in reverse order, they will not be further elaborated and only the various steps of the critical load approach are summarized below. 

This includes soil, vegetation, water (surface and ground), geology, land use etc data, influencing acidification and eutrophication processes in the considered ecosystem. 

For application on a regional scale it also includes the distribution and area of receptor properties (using available digitized information in geographic information systems, GIS). 

This step includes the calculation of critical loads of sulfur, nitrogen and the total acidity in a steady-state situation for the receptors of choice or for all receptors in all cells of EMEP or LoLa grid (150 xl50 km 50 x 50 km 25 x 25km 1 x 1°, 10 x 10 etc.) of a region using a GIS (to produce critical load maps). 

---

General Approaches for Calculating Critical Loads of Heavy Metals Discussing the problems related to the critical load calculation, an attention should be paid to (i) selection of a receptor of concern, (ii) critical limits, (iii) possible calculation methods, (iv) the necessary input data and (v) the various sources of error and uncertainty (de Vries andBakker, 1998a, 1998b). 

---