Environmental factors which influence the sink of silica in the limnetic system of the large monomictic Lake Biwa and its watershed in Japan |
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Authors: | Naoshige Goto Takuro Iwata Tetsuji Akatsuka Masakazu Ishikawa Masaki Kihira Hisayuki Azumi Kaori Anbutsu Osamu Mitamura |
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Institution: | (1) Limnological Laboratory, School of Environmental Science, The University of Shiga Prefecture, 3165 Hassaka-machi, Hikone, Shiga 522-0057, Japan;(2) Gifu Prefectural Hida High School, 763 Sanfukuji-cho, Takayama, Gifu 506-0807, Japan;(3) Institute of Applied Environmental Geoscience Co., Ltd., 30 Aioi-machi, Higashi-ku Nagoya, 461-0012, Japan |
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Abstract: | Dissolved silica (DSi) and its associated biological and physicochemical factors were measured in Lake Biwa, Japan and its
watershed from 2002 to 2003 in order to clarify seasonal variations in the magnitude of the sink of silica and the factors
that influence it within the limnetic system. Consequently, it is concluded that Lake Biwa is a noticeable body of water where
a massive sink of silica is caused. Calculated silica sedimentation in Lake Biwa was 2.0 × 107 kg Si year−1 (7.1 × 108 mol Si year−1) which is equivalent to about 80% of the annual inflow discharge of DSi to Lake Biwa. The magnitude of the sink varies seasonally
by increasing in the winter holomictic stirring period, since it is greatly affected by the species composition of phytoplankton,
the load of phosphorus and the condition of stratification. It seems reasonable to suppose that the DSi in Lake Biwa is removed
mainly by biological processes, i.e., the assimilation of DSi by large centric diatoms and its accumulation in their frustules.
Such silica sinks occur naturally in deeper stagnant waters, providing extended water residence time and supplying a certain
amount of nutrients. These findings indicate that an increase in nutrient loads and abundance of stagnant water due to the
construction of large dams lead to an expansion in the magnitude of the silica sink in a limnetic system. |
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Keywords: | Biogenic silica Diatom Dissolved silica Silica deficiency hypothesis Sink of silica Stagnant waters |
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