Fig. 3.

The inclusion of bacterially mediated CO₂ emission from lakes and rivers in a simplified watershed C budget. The conceptual depiction distinguishes lake C emissions that originate from direct DIC injection to lakes from the bacterial respiration of both recent and ancient terrestrial OC. The model combines published ranges for the main fluxes for northern temperate landscapes (34–38), our own previous estimates of C emissions for these lakes (3), and average estimates of CO₂ fluxes originating from bacterial respiration of recent and old terrestrial OC as described in Methods. All rates are expressed per meter² of total landscape and thus, are comparable.