Stable isotope analysis of benthic fauna and their food sources in boreal lakes

AbstractThe origin of organic C supporting zoobenthic communities in 8 boreal lakes with different concentrations of dissolved organic C (DOC) was assessed by stable-isotope analysis. Profundal zoobenthos was depleted in 13C compared to littoral zoobenthos, and this difference increased with decreasing DOC concentration. The δ13C of littoral zoobenthos suggested reliance on benthic algae, whereas depleted 13C of profundal zoobenthos could be explained by contributions from allochthonous and autochthonous C sources. In deeper lakes, profundal zoobenthos diets also included C processed by methanotrophic bacteria. Littoral zoobenthos δ13C decreased with increasing DOC concentration in the lake water. Our results suggest that littoral benthic fauna are mainly supported by benthic algae in low-DOC lakes and by phytoplankton and allochthonous organic C in high-DOC lakes and that this difference is a result of light absorbance and energy supply by allochthonous organic C. Increasing allochthonous DOC inputs, as ...