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Acid deposition is widespread in Japan, but acidification of stream water is rare in forest ecosystems. Bedrock‐derived cations, including those released into the soil by weathering of bedrock minerals, generally act to neutralize acid deposition and flow out into streams. Volcanic ash, which is widespread in Japan, may also release cations and neutralize acids, but the contribution of volcanic‐ash‐derived cations is currently poorly explored. To assess the importance of volcanic ash as a source of base cations, we examined strontium in two catchments underlain by chert bedrock at Mount Amamaki, Japan. Additionally, we obtained comparative data from two sandstone‐bedrock catchments in the same area. We measured 87Sr/86Sr ratios in samples of stream water, bulk precipitation, riverbed rock, and soil from the catchments. We used the 87Sr/86Sr data to analyze the relative contributions of atmospheric deposition, bedrock, and volcanic ash in soil as sources of Sr in the stream waters. We estimated volcanic ash in soil to contribute between 46% and 78% of stream‐water Sr for one chert‐bedrock catchment, and between 0% and 52% for the other. We conclude that volcanic ash in soil is an important source of Sr in stream water. Thus, volcanic ash can act as a source of base cations and hence contribute to the acid‐neutralizing capacity of soil in forest ecosystems in Japan. [ABSTRACT FROM AUTHOR]

Dry deposition fluxes (F L) of NO3 − and SO4 2− to leaf surfaces were measured for Japanese red pine (Pinus densiflora), Japanese cedar (Cryptomeria japonica), Japanese cypress (Chamaecyparis obtusa), and Japanese white oak (Quercus myrsinaefolia), together with atmospheric concentrations (C L) of NO x (NO+NO2), T-NO3 (gaseous HNO3 +particulate NO3 −) and SO x (gaseous SO2 +particulate SO4 2−) around the leaves in a suburban area of Japan, using a modified leaf-washing technique. F L of NO3 − and SO4 2− decreased as follows: pine>>cedar>cypress≥oak and pine>>cedar>oak≥cypress, respectively. F L of NO3 − for all tree species fluctuated synchronously with C L of T-NO3. F L of SO4 2− fluctuated with C L of SO x , but the dominant pollutant deposited (SO2 or SO4 2−) appeared to differ for different tree species. Dry deposition conductance (K L) of T-NO3 and SO x was derived as an F L/C L ratio. Seasonal variations of K L likely reflect the gas/particle ratios of T-NO3 and SO x , which were affected by meteorological conditions such as temperature. Dry deposition velocities (V d) of T-NO3 and SO x were obtained as the mathematical product of annual mean K L and the total leaf surface areas in the forests. The comparison of V d among tree species indicated that the loads of acidic air pollutants were higher to coniferous forests than broad-leaved forest because of the higher K L and/or larger leaf surface areas. [Copyright &y& Elsevier]

Abstract: Speciation of Al, including inorganic monomeric Al (Ali, the sum of aquo, hydroxy and inorganically complexed forms), organic monomeric Al (Alo, the organically complexed form), and colloidal mineral Al (Alc, the fine particulate form that passes through a 0.4-μm pore size membrane filter), was investigated in stream waters (pH 6–8) of 4 watersheds in Japan. Total dissolved Al (Alt, the sum of Alc, Ali and Alo) ranged from 0.03 to 3.31μM, and Alc was a minor component (<22% of Alt) in most of the streams. Ali was dominant (71% of Alt) in stream waters with low concentrations of Alt (<0.25μM), while the Alo fraction (37%) was almost as large as the Ali fraction (39%) in the highest class (Alt >1μM). In spite of the variation in the range of reactive Al (Alr, the sum of Ali and Alo) in the 4 watersheds (Miomote, 0.03–3.27μM; Tsukuba, 0.06–0.71μM; Dorokawa, 0.05–0.71μM; Tama, 0.03–0.38μM), the entire data set for Alr could be expressed as a function of the ratio of dissolved organic C (DOC) and Ca: [Al r (μM)]= 0.13 [DOC/Ca (mol/mol)]+0.11 (r =0.86, P <0.001). Alr increased in proportion to the DOC/Ca ratio in Japanese stream waters. Although acidic deposition in Japan has already resulted in elevated concentrations of in stream waters, a high level of Ca (instead of Al) is serving as a major counterion for . However, an additional loading of acidic deposition may result in shortage of Ca and mobilization of Al as a counterion for , and continuous observation of the speciation of Al in Japanese stream waters may reveal future change in the conditions for mobilization of Al from “low Ca and high DOC” to “low Ca and high ”. [Copyright &y& Elsevier]