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The production-to-respiration ratio and its implication in Lake Biwa,Japan
Authors:Email author" target="_blank">Jotaro?UrabeEmail author  Takehito?Yoshida  Tek?Bahadur?Gurung  Tatsuki?Sekino  Narumi?Tsugeki  Kentaro?Nozaki  Masahiro?Maruo  Eiichioro?Nakayama  Masami?Nakanishi
Institution:(1) Center for Ecological Research, Kyoto University, Otsu, Japan;(2) School of Environmental Science, University of Shiga Prefecture, Hikone, Japan;(3) Present address: Division of Ecology and Evolutionary Biology, School of Life Sciences, Tohoku University, Biological Buildings, Aoba, Sendai 980-8578, Japan;(4) Present address: Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA;(5) Present address: Fisheries Research Division, Nepal Agricultural Research Council, Katmandu, Nepal;(6) Present address: Research Institute for Humanity and Nature, Kyoto, Japan;(7) Present address: School of Human Science, Sugiyama Jogakuen University, Nagoya, Japan;(8) Present address: Shiga-cho, Japan
Abstract:Production-to-respiration (P:R) ratio was estimated at an offshore site of Lake Biwa in order to examine whether the plankton and benthic community is subsidized with allochthonous organic carbon, and to clarify the role of this lake as potential source or sink of carbon dioxide. The respiration rate of protozoan and metazoan plankton was calculated from their biomass and empirical equations of oxygen consumption rates, and that of bacterioplankton was derived from their production rate and growth efficiency. In addition, the carbon mineralization rate in the lake sediments was estimated from the accumulation rate of organic carbon, which was determined using a 210Pb dating technique. On an annual basis, the sum of respiration rates of heterotrophic plankton was comparable to net primary production rate measured by the 13C method. However, when the mineralization rate in the lake sediments was included, the areal P:R ratio was 0.89, suggesting that Lake Biwa is net heterotrophic at the offshore site with the community being subsidized with allochthonous organic carbon. Such a view was supported by the surface water pCO2 that was on average higher than that of the atmosphere. However, the estimate of net CO2 release rate was close to that of carbon burial rate in the sediments. The result suggests that the role of Lake Biwa in relation to atmospheric carbon is almost null at the offshore site, although the community is supported partially by organic carbon released from the surrounding areas.
Keywords:Carbon budget  Heterotrophs  Lake metabolism  pCO2  P:R ratio
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