Seasonal changes of silicate’s distribution in lake sediments

Author(s): Park Jayeong
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Institution or organization of origin: Shimane University
Country: Japan


Seasonal increases in dissolved silicate (DSi) in the lake bottom environment were observed with an increase of hydrogen sulfide (H2S). This phenomenon became more apparent in the summer as the anoxic-reducing environment was enhanced. Therefore, we hypothesized that the H2S concentrations would directly affect the silicate elution from sediments. Furthermore, we investigated the annual change in concentrations of DSi and H2S in pore water and examined the anoxic elution process of silicate in sediments. The DSi distributions in pore water of December were lower than 0.5 mM for Lake Biwa (a freshwater lake) and 1.2 mM for Lake Nakaumi (a brackish lake), and the H2S concentrations were 0 and 6.4 mM, respectively. In July, maximum DSi concentrations were increased up to 1.1 mM in Lake Biwa and 4.7 mM in Lake Nakaumi. The H2S concentrations were also increased to 0.2 and 7.7 mM, respectively. A simple experiment was conducted to determine the effect of H2S on the elution of silicate in the sediment environment. The Na2S solution (pH 7.0) was added to sediment samples from Lakes Biwa and Nakaumi. After leaving for 10 minutes, 2.4 and 1.5 mM of DSi were eluted from Lakes Biwa and Nakaumi samples, respectively. After leaving for 24 hours, DSi concentrations were increased to 25 mM and 2.0 mM, respectively. Consequently, these results suggest that changes in H2S concentration play an important role in the anoxic elution process of silicate, even if the lake bottom environment maintains anoxic throughout the year.

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