Regeneration of Silicic Acid from Sediment in Lake Biwa, Japan

The uptake of silica by SiOrsecreting organisms (called a "silicate pump" by DuGDALE et al. 1995) decreases the silicic acid (Si(OH)4) concentration in surface lake waters. Biogenic silicon (BSi) that accumulates in sediments by the silica pump is regenerated by biogeochemical decomposition and molecular diffusion from sediments to the overlying waters. The regeneration rate of Si(OH)4 in sediment varies both spatially and temporally (WETZEL 200 l) because decomposition o f B Si in sediment is influenced by temperature, pH, aluminum, and ferric oxyhydroxides {NRIAGU 1978, RIPPEY 1983). In Lake Biwa, the Si(OH)4 concentration is low in epilimnion (0-30 J.!M; ÜHYAMA et al. 1974, GoTO et al. 2007). The silica pump is likely responsible for the low Si(OH)4 concentration-limited diatom growth (SCHELSKE & STOERMER 1971 ). The bottom waters {>70 m) Si(OH)4 concentration have increased to about 30 JlM since the 1980s in the north basin of Lake