Relationships between DOC concentration and epilithon stable isotopes in boreal lakes

Littoral biota in boreal lakes are known to assimilate epilithon. Being able to predict the stable isotopic composition of these alga will help to identify those systems in which δ 13 C and δ 15 N analysis can be used in foodweb investigations of allochthony and biomagnification. 2. In a survey of 15 boreal lakes, the concentration of dissolved organic carbon (DOC) explained 76% of the variation in epilithon δ 13 C, and 86% of the variation in epilithon δ 15 N. 3. Because both δ 13 C and δ 15 N values were depressed and similar to terrestrial values in humic (high DOC) lakes, it will be more difficult to successfully employ stable isotopic techniques for estimating allochthony in such systems. Lower δ 15 N values in humic lakes also indicate that trophic positions estimated by stable isotopes are not directly comparable to those of similar biota inhabiting clearwater lakes, unless autochthonous baseline corrections are made.