Speciation of Aluminum in Lake Kasumigaura, Japan

Abstract

Speciation of aluminum (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 circumneutral (pH 7–9) eutrophic Lake Kasumigaura, Japan. The mean concentrations calculated from the result of monthly observations during the period from January to December 2003 were compared among ten stations. Ali decreased downstream from the mouth of the influent rivers (0.07–0.10 μM) to the mouth of the effluent river (0.03 μM). Alc, which also decreased downstream (from 0.11 to 0.06 μM), was the major fraction (>50%) of total dissolved Al at all stations. Alo remained around 0.02 μM at all stations. In Lake Kasumigaura, a high concentration of Si (average 0.23 mM) seems to be involved in the removal of Ali and formation of Alc. Also, a high concentration of Ca (ave. 0.43 mM) seems to be acting as a competitive cation for complexation with a high concentration of dissolved organic carbon (ave. 0.26 mM), and inhibit the formation of Alo.