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首页> 外文期刊>Journal of paleolimnology >Assessment of carbon isotopic signature of Daphnia ephippia as a proxy for past carbon transfers to pelagic food webs in Jura lakes
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Assessment of carbon isotopic signature of Daphnia ephippia as a proxy for past carbon transfers to pelagic food webs in Jura lakes

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Previous studies suggested that past changes in carbon sources and pathways in pelagic food webs can be investigated using carbon isotopic analysis (d(13)C) of ephippia, resting-eggs produced by Daphnia. However, ephippia are known to be produced by Daphnia within a relatively short time window. Moreover, d(13)C(Daphnia) value may vary considerably over the annual cycle of lakes due to seasonal variations in the availability of the different carbon sources for pelagic consumers, such as phytoplankton or methanogenic carbon, under the effect of stratification and turnover mechanisms. As a result, the information provided by d(13)C(ephippia) can mainly depend on the timing of ephippia production with respect to the timing of lake autumnal turnover. Nevertheless, there is still limited information in the literature about the timing of ephippia production in relation to the seasonal variability of d(13)C(Daphnia). However, it may have important implications for the use of carbon isotopic signature of ephippia as a paleoecological proxy of pelagic carbon transfers in stratified lakes. In this study, we combine a limnological survey on nine French lakes with a paleolimnological approach on three sediment cores to identify the factors controlling the integration period of d(13)C(ephippia) and to assess the relevance of using d(13)C(ephippia) as a proxy for pelagic carbon transfers in paleolimnological studies. Our limnological survey of nine lakes suggests that d(13)C(ephippia) depends mainly on the timing of autumnal turnover. Lakes with the earliest turnover had lower ephippia d(13)C due to methanogenic carbon transfer in the pelagic food web after autumnal turnover, whereas lakes with later autumnal turnover had higher d(13)C(ephippia), mainly reflecting phytoplankton consumption by Daphnia during stratification period. Consequently, potential shifts over time in lake turnover timing relative to ephippia production period may lead to the misinterpretation of d(13)C(ephippia) variations in sediment records. Our paleolimnological study on three lakes shows that complementary d(13)C analysis of other Daphnia remains like claws, reflecting a time-integrated average isotopic signature of the Daphnia source population, can help to identify potential changes in the integration period of d(13)C(ephippia) and avoid misinterpretation of stratigraphic and temporal d(13)C(ephippia) trends regarding carbon sources fuelling pelagic consumers.

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