Critical Loads for Sulphur and Nitrogen

Summary

A group of Nordic experts has tried to draw conclusions on critical loads for sulphur and nitrogen. The critical load is defined as “The highest load that will not cause chemical changes leading to long-term harmful effects on most sensitive ecological systems”.

Most soils, shallow groundwaters and surface waters would probably not be significantly changed by a load of 10–20 keq H⁺·km²·yr⁻¹ in areas with a low content of base cations in the deposition. The total deposition of hydrogen ions in southwestern Scandinavia is in the order of 100 keq ·km⁻²·yr⁻¹.

The long-term critical load for nitrogen is in the range of 10–20 kg N·ha·¹-yr⁻¹ in most forest ecosystems. In high productive sites it might be as high as 20–45 kg N·ha⁻ yr⁻¹ in southern Sweden, and amounts to 30–40 kg·ha⁻¹·yr⁻¹ and even more over large areas in central Europe.

The current deposition of sulphur and nitrogen must be substantially reduced to keep the long-term changes in sensitive ecosystems within acceptable limits.