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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 22
Biogeosciences, 12, 6781–6789, 2015
https://doi.org/10.5194/bg-12-6781-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 12, 6781–6789, 2015
https://doi.org/10.5194/bg-12-6781-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 26 Nov 2015

Research article | 26 Nov 2015

Chlorophyll a-specific Δ14C, δ13C and δ15N values in stream periphyton: implications for aquatic food web studies

N. F. Ishikawa1, M. Yamane1,2, H. Suga1, N. O. Ogawa1, Y. Yokoyama1,2, and N. Ohkouchi1 N. F. Ishikawa et al.
  • 1Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan
  • 2Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan

Abstract. Periphytic algae attached to a streambed substrate (periphyton) are an important primary producer in stream ecosystems. We determined the isotopic composition of chlorophyll a in periphyton collected from a stream flowing on limestone bedrock in the Seri River, central Japan. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) and natural radiocarbon abundances (Δ14C) were measured in chlorophyll a13Cchl, δ15Nchl and Δ14Cchl) and bulk (δ13Cbulk, δ15Nbulk and Δ14Cbulk) for periphyton, a pure aquatic primary producer (Cladophora sp.) and a terrestrial primary producer (Quercus glauca). Periphyton δ13Cbulk and δ13Cchl values did not necessarily correspond to δ13Cbulk for an algal-grazing specialist (Epeorus latifolium). Periphyton Δ14Cchl values (−258 ‰ in April and −190 ‰ in October) were slightly lower than Δ14Cbulk values (−228 ‰ in April and −179 ‰ in October) but were close to the Δ14C value for dissolved inorganic carbon (DIC; −217 ± 31 ‰), which is a mixture of weathered carbonates (Δ14C = −1000 ‰), CO2 derived from aquatic and terrestrial organic matters (variable Δ14C) and dissolved atmospheric CO214C approximately +30 ‰ in 2013). Δ14Cchl values were also close to Δ14Cbulk for E. latifolium (−215 ‰ in April and −199 ‰ in October) and Cladophora sp. (−210 ‰), whereas the Δ14Cbulk value for Q. glauca (+27 ‰) was closer to Δ14C for atmospheric CO2. Although the bulk isotopic composition of periphyton is recognised as a surrogate for the photosynthetic algal community, natural periphyton is a mixture of aquatic and terrestrial organic materials. Our results indicate that the bulk periphyton matrix at the study site consists of 89 to 95 % algal carbon (derived from 14C-depleted DIC) and 5 to 11 % terrestrial organic carbon (derived from 14C-enriched atmospheric CO2).

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We determined the isotopic composition of chlorophyll a in periphytic algae attached to a streambed substrate (periphyton). Although the bulk isotopic composition of periphyton is recognised as a surrogate for the photosynthetic algal community, our results indicate that the bulk periphyton matrix at the study site consists of 89 to 95% algal carbon and 5 to 11% terrestrial organic carbon. We show that the chlorophyll a isotopic composition is a useful tracer for the aquatic food web studies.
We determined the isotopic composition of chlorophyll a in periphytic algae attached to a...
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