Responses of Benthic Carbon Flows in Scandinavian Lakes to Atmospheric Sulphur and Nitrogen Depositions: Potential Influence of Nutrient Limitation

ABSTRACT Paleolimnological reconstructions of past changes in carbon stable isotopic composition of chironomid head capsules (δ 13 C HC ) were used to quantify the impacts of atmospheric sulphur and nitrogen depositions on carbon processing at the base of lake food webs. We hypothesised that the impacts of atmospheric nitrogen deposition on carbon flows through food webs are influenced by nutrient limitation, as increasing nitrogen inputs are expected to drive higher primary producer biomass in nitrogen‐limited lakes, thus increasing its availability for benthic consumers. The δ 13 C HC values showed significant changes before/after 1960, corresponding to the time of early impacts of atmospheric deposition on water chemistry and biological communities in Scandinavian lakes. These results suggest that atmospheric deposition was a key driver of change in carbon flows through benthic food webs. Furthermore, our study showed that lakes responded differently to atmospheric deposition and that differences in δ 13 C HC values were largely explained by a combination of nutrient limitation, latitude and water transparency. Overall, results support the hypothesis that the response of carbon flows through benthic food webs to changes in atmospheric nitrogen deposition differs partly depending on lake nutrient limitation. However, the observed strong collinearity between the explanatory variables complicates the interpretation of the relationships between the temporal changes in benthic carbon flows in response to atmospheric deposition and nutrient limitation.