Hydrologic setting constrains lake heterotrophy and terrestrial carbon fate

Abstract

Current efforts to scale lake processes rely heavily on empirical observations and do not consider inter-lake heterogeneity that is likely to regulate terrestrial dissolved organic carbon (tDOC) decomposition in lakes. We created a simple, analytical model of tDOC decomposition in lakes that highlights the role of lake size and catchment hydrologic export. Our model predicts a hydrologically mediated tradeoff between the instantaneous rate of tDOC decomposition and the fraction of the tDOC load that is decomposed within a lake. We also predict that variation in the importance of evaporation as a hydrologic export generates meaningful variation in tDOC decomposition at a given hydrologic residence time. These patterns of tDOC decomposition that emerge from lakes' hydrologic settings suggest that past attempts to scale lake carbon biogeochemistry may be biased. Our model provides context for empirical studies of lake carbon cycling and enables informed scaling of lake carbon biogeochemistry.