Leaching of Base Cations (Ca2+,Mg2+,K+) from Forest Canopy during Acid Rain

Abstract:

Ten plots were used to study the interception deposition, total canopy leaching, base cations from canopy leaching, and the H+ and NH4+ uptake by the canopy in subtropical coniferous-broadleaved mixed forest in Shaoshan, Hunan Province, from January 2001 to June 2002. The predominant elements in wet deposition in the forest were Ca²⁺, Mg²⁺ and K⁺. Ca²⁺ from canopy leaching was high, amounting to 155.34 mmol m^-2a^-1, followed by K⁺ (84.13 mmol m^-2a^-1) and Mg²⁺ (30.74 mmol m^-2a^-1). Large amount of Ca²⁺ leaching indicated that it was the main acidity bufering agent from can opy leaching，suggesting the potential harmfulness of acid rain to the forest．Seasonal changes in the amount of base cations from canopy leaching were in the order of winter> spring> summer>autumn，but the proportion of total leaching were summer(58.4％)>spring(54.1％)>winter(51.4％)>autumn (32.5％)．Seasonal uptake of NH₄⁺ by the canopy in the year observed varied from 30 to 100 mmol m^-2，and that of H⁺ from 30 to l80 mmol m^-2．