Canopy leaching of subtropical mixed forests under acid rain

Abstract

Leaching of major ions from acid precipitation in a subtropical forest was examined based on an experiment in four sample sites in Shaoshan City, Hunan Province, China, from January 2001 to June 2002. Results clearly show that when rain passed through the canopy, pH increased and the evidence of ion uptake was presented for SO₄^2-, NO₃^-, Mg²⁺ and NH₄⁺ ions, especially of NH₄⁺ and NO₃^-. The percentages of dissolved SO₄^2-, Ca²⁺ and Mg²⁺ show a decreasing trend with increasing rainfall. Percentages of leaching Ca²⁺, K⁺ and Cl^- ions show an increasing trend as a function of increased pH values. The forest canopy in Shaoshan City has a strong effect on the uptake of SO₄^2- and NO₃^- ions under acid rain conditions. The decreasing order of ions leaching in the forest canopy is as follows: K⁺ > Ca²⁺ > Cl^- > Mg²⁺ > SO₄^2- > NO₃^- > NH₄⁺ > Na⁺.

Keywords

acid deposition / leaching and uptake / subtropical forest / Shaoshan City