Patterns and controls of carbon stable isotope composition of particulate organic matter in subtropical lakes

The stable carbon isotope composition (delta C-13) of particulate organic matter (POM) has been used to infer sources of organic matter and major biogeochemical processes in lakes. However, very few studies have compared the delta C-13(POM) among lakes of different limnological properties. Here, we report such an analysis to understand the patterns and controls of stable isotopes of POM from 96 lakes in Florida, USA. Results indicated that delta C-13(POM) increased significantly with the increases in lake area, pH and trophic state, but decreased with the increase in CO2 concentration and water color content. delta C-13(POM) in a small set of these lakes showed a positive relationship with delta C-13 of dissolved inorganic carbon (DIC). There was a widespread C-13 depletion of POM in the study lakes, especially in lakes with high water color, suggesting allochthonous subsidy of phytoplankton production. Multiple regression models pointed to the importance of trophic state, color and pH. This study demonstrated that the delta C-13(POM) is indicative of carbon source, trophic state and ecosystem metabolism in lakes.