Benthic-pelagic equilibrium of carbon transfer in high-altitude lakes: featuring the role of lake’s characteristics and seasonal variation

Abstract

Carbon pathways in freshwater ecosystems are particularly complex because of the multiple origins, forms, and transformations of carbon by aquatic organisms. In high-altitude lakes, located above the treeline, most of the carbon pool is of indigenous origin. However, little is known about the influence of lake and watershed characteristics on carbon transfer pathways and their variability over an annual cycle. We analyzed simultaneously carbon stable isotopic composition (δ¹³C) and C/N ratio of organic matter from pelagic (POM, zooplankton) and benthic components (benthic invertebrates, sediments) in eight high-altitude lakes and hypothesized that the origin of the carbon used and the composition of organic matter in the pelagic and benthic compartments vary according to the lake’s characteristics. The results showed that most of the organic matter composing the sediments is of autochthonous origin, regardless of the lake’s characteristics. We observed a common tendency of seasonal shift in the source of carbon used, from a C–CO₂ respired or a C–CH₄-derived in early summer to a C–CO₂ dissolved in late summer. However, the origin of the carbon used and the contribution of pelagic and benthic primary producers to the carbon transfers varied according to the lakes’ depth, lithology, and food web structure. These findings highlight that the complexity of high-altitude lakes and how the balance between benthic and pelagic food webs will be important in future ecological trajectory predictions.