酸雨作用下的森林冠层盐基离子(Ca^(2+),Mg^(2+),K^+)淋洗

Leaching of Base Cations (Ca^(2+),Mg^(2+),K^+) from Forest Canopy during Acid Rain

在韶山针阔叶混交林中设立了10个30m×30m的样方,对1年中各个季节的森林截留沉降、降雨后树冠层总滤出量、盐基离子滤出量以及树冠层对H+和NH4+的摄入量进行了分析和估算。韶山森林湿沉降成分中以Ca2+为主,Mg2+,K+含量较低。树冠层盐基离子总滤出量中Ca2+最高,达到155.34mmolm-2a-1,Mg2+最低,为30.74mmolm-2a-1,K+居中,为84.13mmolm-2a-1。Ca2+的大量滤出表明它是树冠层缓冲降水酸度的主要介质,同时也表明酸雨对韶山森林的潜在危害,其在总滤出量中的比重的季节变化是:夏(58.4%)>春(54.1%)>冬(51.4%)>秋(32.5%)。盐基离子的滤出量以冬→春→夏→秋依次递减,但是树冠层季节摄入NH4+的量在30-100mmolm-2,而对H+的摄入量则在30-180mmolm-2。

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 buffering agent from canopy 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 180 mmol m-2.