Composition and behavior of aluminum ions and colloidal aluminosilicates in acidified terrestrial waters

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Abstract
The composition of aluminum in seven acidified lake and river waters in the Tohoku district was studied, and Al3+ and hydroxy-Al (HA) ions were identified in the acidified waters. These acidified terrestrial waters contained a small but significant amount of hydroxyaluminosilicate (HAS) ions. Colloidal alumino- silicates (>0.2 μm) identified in the waters were characterized by the predomi- nance of proto-imogolite allophane and/or allophane. The white precipitates and gelatinous materials formed in the acidified terrestrial waters were com- posed of precipitated allophane. The acidic substances of the terrestrial waters were mainly composed of Al3+, HA, and HAS ions. HAS ions and HAS colloids were first identified in the lake and river waters. The presence of HAS ions and HAS colloids in the waters provides valuable information on the formation mechanism of precipitated allophane in the acidified terrestrial waters. The reaction giving a peculiar bluish-white color in some lakes could arise from HAS colloids suspended in the waters. There was an equilibrium relationship among HA and HAS ions, HAS colloids, and HAS sediments (allophanic) formed in the acidified terrestrial waters. The chloritization of paddy soils caused by acidified irrigation waters and the unfavorable effect on fish breeding were predominantly due to Al3+ and HA ions in acidified terrestrial waters.