Carbon-13/Carbon-12 Variation in Subalpine Lake Aquatic Insects: Food Source Implications

Abstract

Relative 13C concentrations were found to be significantly different among the three primary organic carbon sources for aquatic insect production within Findley Lake, Washington, USA. These three carbon sources were conifer tree detritus (mean δ18C = −27.3 per mil), periphyton (−34.6 per mil), and plankton (−45.9 per mil). Correspondingly, the δ18C of the adults of assumed autochthonous carbon feeders, Paraleptophlebia sp. (Ephemeroptera: Leptophlebiidae) and Chaoborus trivittatus (Diptera: Chaoboridae), well approximated the δ13C of periphyton and plankton, respectively. The remainder of the adult insect emergence, mostly Limnelphilidae and Chironomidae, exhibited δ13C values intermediate between the terrestrial and periphyton carbon. Approximately 38% of the 51 kg C of insect biomass annually emerging from this lake was conservatively estimated to originate from terrestrial plant sources.Key words: carbon-13, carbon pathways, lake, aquatic insects, feeding ecology, insect emergence, terrestrial detritus