Critical loads of sulfur and nitrogen

This paper describes the simple mass balance model (SMB) for calculating critical loads of sulphur and nitrogen on forest soils. It includes a complete overview of the mathematical descriptions for all the relevant input terms in the SMB model such asuptake, nitrogen transformation processes and alkalinity leaching. A distinction is made between methods using a constant and a deposition-dependent description of nitrogen sinks, such as denitrification. The simultaneous treatment of sulphur and nitrogen does not allow the calculation of a unique critical load. In this context, the concept of a protection isoline is introduced and mathematically described.