『Abstract
Speciation of Al, including inorganic monomeric Al (Ali,
the sum 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:
[Alr (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 NO3- + SO42-
in stream waters, a high level of Ca (instead of Al) is serving
as a major counterion for NO3-
+ SO42-. However, an additional
loading of acidic deposition may result in shortage of Ca and
mobilization of al as a counterion for NO3-
+ SO42-, 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 NO3-
+ SO42-”.』
1. Introduction
2. Samples and analysis
3. Results and discussion
3.1. Concentrations of Alt
3.2. Change in forms of al with increasing Alt
3.3. Comparison of four watersheds
3.4. Conditions for increase in Al
3.5. Relationship between Al, Ca and DOC
3.6. Comparison with previous studies in northern America and
Europa
References