The importance of transport processes and spatial gradients on in situ estimates of lake metabolism

We measured spatial gradients of dissolved oxygen in a eutrophic reservoir from repeated transects over a 5-day period. The equation typically used to compute lake metabolism was extended to the full advection–diffusion–reaction equation, which includes transport terms. These transport terms were computed and found to be of similar magnitude to the rate of change of dissolved oxygen. We demonstrate that neglecting transport terms in this reservoir could lead to over-estimates in net ecosystem production calculations in the surface layer of up to 100%. We advocate the calculation of nondimensional Peclet and Damkohler numbers in future studies to assist in determining the importance of transport terms on lake metabolism estimates.