Ann. Limnol. - Int. J. Lim.
Volume 49, Number 2, 2013
|Page(s)||139 - 147|
|Published online||18 June 2013|
Highly efficient silica sink in monomictic Lake Biwa in Japan
1 School of Environmental Science, The University of Shiga Prefecture, 2500 Hassaka-cho, Hikone, Shiga 522-8533, Japan
2 Iga Community-Based Research Institute, Mie University, 1-3-3 Yumegaoka, Iga, Mie 518-0131, Japan
3 Fisheries and Environmental Oceanography, Graduate School of Agriculture, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan
* Corresponding author: firstname.lastname@example.org
Received: 25 June 2012
Accepted: 6 April 2013
In order to clarify the mechanisms underlying high efficiency of the silica sink in monomictic Lake Biwa in Japan, vertical flux of biogenic silica (BSi) was measured using sediment traps over a period of 15 months. The sediment traps were deployed at depths of 30 and 70 m. On a global scale, BSi fluxes in Lake Biwa were very high, ranging from 20 to 1087 mg Si.m−2.d−1 at the 30 m trap and 12–999 mg Si.m−2.d−1 at the 70 m trap throughout the observation period. The BSi fluxes at both traps increased significantly during the winter period and the ratio of BSi fluxes in the winter period to annual BSi fluxes ranged from 27 to 62%. In the winter period, when nutrients are supplied from the hypolimnion to the epilimnion, the distribution of photosynthetically active diatoms was almost homogeneous in all layers, including the aphotic layer. At this time, the diatoms assimilated dissolved silica (DSi) in a wider layer containing a part of aphotic layer in order to produce rigid frustules, which accumulated rapidly in bottom sediments as DSi concentration in the water column decreased. Thus, size of the silica sink in Lake Biwa is enhanced during the winter holomictic mixing period through interaction between physical (thermocline disruption: transfer of diatoms to deep layers by vertical convection), chemical (nutrient supply from deep layers) and biological (dominance of active diatoms in all layers) processes.
Key words: Silica sink / biogenic silica (BSi) / diatom / vertical flux / Lake Biwa
© EDP Sciences, 2013
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