Changing Patterns of Nitrogen and Sulfur Deposition

In a first step, nutrient-depleted soils with low buffering capacity are identified to a,s,sess regions with potential for destabilization of forest ecosystems by acid deposition. Becau.se the acidity neutralization capacity of. soils (ANC) cannot be accurately determined from the global data, a simple approach based on the Soil Map of the World (FAO, 1995) is carried out. To evaluate the buffering capacity of the top.soils, the CEC data (cation exchange capacity) and the base saturation data (Na, K, Mg, and Ca) are combined with a map of the global distribution of forests (WCMC, 1997) to obtain the measures for fore.st soils with low buffering capacity. 

In relation to add input from 1980 to 1990, the buffering capacity of 1.8 Mio km or 15% of the acid-sensitive forest soils tends to become saturated in the next 25-100 years. Under the assumptions of the IS92a scenario, this share more than doubles and increases to 4.0 Mio km or 34% between 2040 and 2050. For 1980-1990, the mean buffering capacity of these sols based on our methodology is supposed to last for 65 years more. Under changed inputs this period tends to decrease for 2040-2050 to 

50 years, which is less than half the lifetime of most of the managed tree species. For 1980-1990, four regions are mainly affected by acid deposition the Eastern part of Northern America, Europe, Scandinavia with the Northwestern Russian Federation, and Southern China. The situation for 2040-2050 changes in such a way that the old hotspots are still present but the area of saturation increases only moderately with the main increase taking place in the tropical and subtropical regions of South America and South and Southeast Asia (see Fig. 3 see also color insert). 

---