Influence of acid snowmelt on the chemistry of stream water in the forest watersheds of the cold and snowy region, Japan

本文对北海道北部森林流域酸性融雪的发生及其对土壤的影响进行了一系列观测。研究结果如下：1.山区小流域积雪化学组成受森林影响较大，与海拔关系不大。开阔地带的积雪呈酸性。另一方面，森林中的那些显示出较低的酸度和较高的离子浓度。这些发现表明，森林不仅缓冲了积雪的酸度，而且对截留干燥沉积物也有影响。初始融雪的pH值小于4.0，然后迅速增加，随着融化的进展。在融化期间，从积雪中观察到离子物种的连续洗脱。解冻过程中约有70%的H^+被溶出，并随着前20%的融水（化学分馏）而损失，这表明在解冻开始时有强烈的酸释放。虽然强大的酸释放是明显的融水，pH值的下降是模糊的森林流域的溪流。分析认为，第三纪岩石集水区的融水渗透较深，而蛇纹岩集水区的河水HCO_3^-浓度较高。此外，也有可能是森林流域的积雪酸度降低。Ca^2+、Mg^2+和HCO 3 ^-的输出量大于积雪输入量，表明它们在一定程度上是通过流域内部的土壤地球化学过程提供的。解冻期后，微生物的呼吸作用对流域内HCO_3^-的产生起着重要作用，HCO_3 ^-是流域内主要的质子源。

A series of observation was carried out to investigate the occurrence of acid snowmelt and its influence on the in the forest watersheds of northen Hokkaido. The results are as follows :1. The chemical composition of the snowpack of the watershed in mountain area was strongly affected by the presence of forest and had little relation with altitude. The snowpack on open area was acidic. On the other hand, those in forests showed lower acidity and higher ionic concentrations. These findings indicate that forests not only buffer the acidity of snowpack but also have an effect on trapping dry deposits.2. The pH of initial snowmelt was less than 4.0 and then rapidly increased as the progression of melting. A Continuous elution of ionic species was observed from the snowpack during the thaw period. Approximately 70% of H^+ eluted out during the thaw was lost with the first 20% of meltwater (chemical fractionation) , which indicated the strong release of acid in the beginning of the thaw.3. Although strong release of acid was evident for the meltwater, the decrease of pH was obscure in the streamwater of forest watersheds. Following reasons were considered : the meltwater penetrated into the deeper part in case of the watersheds of the rocks in tertiary period ; the streamwater had high HCO_3^- concentration in case of the watersheds of serpentine rocks. In addition, it was also possible that the forest on the watersheds decreased the acidity of the snowpack.4. As for Ca^<2+>, Mg^<2+> and HCO_3^-, their output from the watershed exceeded their input from the snowpack, which indicated they were supplied, to some extent, from the inside of the watersheds via biogeochemical processes. The respiration of microorganisms acted an important role for the generation of HCO_3^- Which was dominant proton source inside the watersheds after the thaw period.