Productivity and heterotrophy influences on Zooplankton δ13C in northern temperate lakes

Abstract

Although a range of over 30 ‰ in stable carbon isotope ratios has been recorded for freshwater plankton, no extensive synoptic survey has been undertaken to examine whether any environmental or ecophysiological determinants of δ13C exist. Here we reanalyze existing literature data on the seasonal variation in plankton δ13C from eutrophic lakes, and collect new data on mid-summer zooplankton δ13C from 52 Canadian Shield lakes, to demonstrate that plankton become enriched in 13C relative to 12C under conditions of high productivity and low pCO2. Low zooplankton δ13C signatures in humic/dystrophic lakes of high DOC (dissolved organic carbon) concentration and colour, and in clear-water lakes with high rates of epilimnetic respiration and hypolimnetic metabolism, suggest that the 13C-depletion observed in oligotrophic lakes is probably due to heterotrophic activity. © Inter-Research 1997.