森林降水化学的变化特征和机理

研究并比较了湖南酸雨区韶山小集水区林内降水的化学特征，结果表明，与大气降水相比，穿冠水和地表穿透水中的富集的离子浓度除了NO3^-和Na^ 外均明显增加，到达地表的降水离子增加倍数最高达34．3倍；离子总量最高倍数为8．1倍，乔木树冠层的离子富集作用大于灌木层。韶山的大气降水、穿冠水和地表穿透水的年均pH分别为4．61、5．54和5．85。持续大量的降水对森林上空的污染物有较高的清除效果。

Variation of chemical properties and the mechanisms of the forested precipitation

The study on the chemical properties of the forested precipitation was carried out in Shaoshan catchment, Hunan province. The results show that the ionic enrichment concentrations in both the canopy throughfall and the ground-fall significantly increase except for NO-3+- and Na++, compared with those of the bulk precipitation. The largest increase of ionic concentrations rises to 34.3 times during the rainfall passage through the canopy and 8.1 times for the total ionic amounts. The ionic enrichment in the canopy is larger than that of the shrub canopy. The annual mean pH values in the rainfall, the throughfall and the ground|fall are 4.61, 5.54 and 5.85, respectively, proving that the acidity of rainfall being much neutralized during the precipitating process.The large amount and continuous rainfall can efficiently remove the atmospheric pollutants above the forest canopy.