Deposition and leaching of sulfur, nitrogen and calcium in four forested catchments in China: implications for acidification.

Here we present the first detailed study on fluxes of sulfur (S), nitrogen (N), and major cations in Chinese subtropical forest catchments. Data are from four study sites, differing in inputs of atmospheric pollutants and sensitivity to acidification. Results show important differences from most sites in North America and Europe. Dry deposition of S, N, and calcium (Ca) is considerably larger than wet deposition in most cases causing deposition fluxes ranging from moderate to very high, both for acidifying compounds (S deposition 1.5-10.5 kiloequivalents per hectare and year (keq ha(-1) yr(-1)); N deposition 0.4 to 2.5 keq ha(-1) yr(-1)) and for alkaline compounds (Ca deposition 0.8 to 5.7 keq ha(-1) yr(-1)). More than half of the input of acidity is neutralized by alkalinity associated with Ca deposition. Furthermore, the retention of incoming S and N is small in the soil root zone, but considerable in the deeper soils or riparian zone. Drainage water from the root zone of the soils at the two sites with the highest deposition show pronounced acidification. For the two sites with moderate deposition inputs, the root zones are retaining some of the incoming S and buffer some of the incoming acidity. The subsoils and the riparian zonesare strong sinks for N, S, and Ca. This is associated with substantial acid neutralization at all sites. These features are of major importance for the understanding of the long-term effects of acidification in China.