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Food web reliance on allochthonous carbon in two high mountain lakes with contrasting catchments: a stable isotope approach

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Abstract:

The carbon isotopic signature (13C) of dissolved inorganic carbon and food web components was examined in two high mountain lakes. Río Seco Lake is partially surrounded by alpine meadows and has temporal inlets, whereas La Caldera Lake is located on rocky terrain and does not receive inputs from runoff. We assessed whether these contrasting catchments involve differences in the isotopic signature of the food web components and then in the reliance on terrestrial carbon. The 13C of dissolved inorganic carbon was not significantly different between lakes and reflected an atmospheric gas exchange origin. Unexpectedly, bulk particulate organic matter showed enriched 13C values in both lakes, suggesting a terrestrial vegetation influence. Bulk particulate organic matter was exploited mostly by the cladoceran Daphnia pulicaria, whereas the copepod Mixodiaptomus laciniatus was 13C depleted relative to particulate organic matter, indicating a selective feeding on an isotopically lighter source, likely phytoplankton. The results obtained show that, despite contrasting catchments, the food web of both lakes might be partially supported by terrestrial carbon for which utilization is species specific.

Nous avons déterminé les signatures isotopiques (13C) du carbone inorganique dissous et des composantes du réseau alimentaire dans deux lacs de haute montagne. Le lac Rio Seco est partiellement entouré de prairies alpines et possède des tributaires temporaires, tandis que le lac La Caldera est situé sur un terrain rocheux et ne reçoit pas d'apport des eaux de ruissellement. Nous avons examiné si ces basins versants dissemblables entraînent des différences dans les signatures isotopiques des composantes du réseau alimentaire, ainsi que dans les dépendances du carbone d'origine terrestre. Le 13C du carbone inorganique dissous ne diffère pas significativement dans les deux lacs et reflète une origine par échanges gazeux atmosphériques. De façon inattendue, la matière organique particulaire grossière dans les deux lacs montre une enrichissement des valeurs de 13C, ce qui laisse croire à une influence de la végétation terrestre. La matière organique particulaire grossière est surtout exploitée par le cladocère Daphnia pulicaria, alors que le copépode Mixodiaptomus laciniatus est appauvri en 13C par rapport à la matière organique particulaire, ce qui indique qu'il se nourrit de façon sélective d'une source moins riche en isotopes, vraisemblablement le phytoplancton. Les résultats obtenus montrent que, malgré la différence des bassins versants, les réseaux trophiques des deux lacs peuvent être alimentés en partie par du carbone d'origine terrestre, dont l'utilisation varie avec les espèces.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: November 1, 2005

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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