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Aquatic Microbial Ecology

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AME 33:87-94 (2003)  -  doi:10.3354/ame033087

Seasonal dynamics of carbon stable isotope ratios of particulate organic matter and benthic diatoms in strongly acidic Lake Katanuma

Hideyuki Doi1,*, Eisuke Kikuchi2, Shuji Hino3, Takeru Itoh3, Shigeto Takagi1, Shuichi Shikano2

1Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku Sendai 980-8577, Japan
2Center for Northeast Asian Studies, Tohoku University, Kawauchi, Aoba-ku Sendai 980-8576, Japan
3Department of Materials and Biological Chemistry, Faculty of Science, Yamagata University, Yamagata 990-8560, Japan

ABSTRACT: Lake Katanuma is a strongly acidic volcanic lake (average pH 2.2) located in NE Japan in which only 2 algal species are found: Pinnularia acidojaponica, a benthic diatom, and Chlamydomonas acidophila, a phytoplankton species. Although the δ13C of phytoplankton generally varies seasonally in lake ecosystems, in Lake Katanuma the mean δ13C of particulate organic matter (POM, mainly phytoplankton) is constrained to a narrow range from -26.4 to -23.7‰. A major reason for this is the continuous supply of dissolved CO2 gas available to C. acidophila from fumaroles at the lake bottom. The δ13C of P. acidojaponica in Lake Katanuma varied seasonally and was positively correlated with P. acidojaponica abundance at 1 and 4 m depths. This suggests that the higher P. acidojaponica biomass at 1 and 4 m produced the 13C-enrichment in the high-density algal mats because of the limited dissolved CO2 gas. The mean δ13C of benthic diatoms was higher than that of phytoplankton in Lake Katanuma, although the diatoms seemed to assimilate the same carbon source (CO2 gas) in the lake water.

KEY WORDS: Carbon stable isotope · POM · Phytoplankton · Benthic diatoms · Inorganic carbon · Seasonal variation · Acidic conditions

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