Food web reliance on allochthonous carbon in two high mountain lakes with contrasting catchments: a stable isotope approach
Résumé
The carbon isotopic signature (delta(13)C) of dissolved inorganic carbon and food web components was examined in two high mountain lakes. Rio 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 delta(13)C of dissolved inorganic carbon was not significantly different between lakes and reflected an atmospheric gas exchange origin. Unexpectedly, bulk particulate organic matter showed enriched delta(13)C 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 C-13 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.