Modelling CO emissions from water surface of a boreal hydroelectric reservoir.

To quantify CO emissions from water surface of a reservoir that was shaped by flooding the boreal landscape, we developed a daily time-step reservoir biogeochemistry model. We calibrated the model using the measured concentrations of dissolved organic and inorganic carbon (C) in a young boreal hydroelectric reservoir, Eastmain-1 (EM-1), in northern Quebec, Canada. We validated the model against observed CO fluxes from an eddy covariance tower in the middle of EM-1. The model predicted the variability of CO emissions reasonably well compared to the observations (root mean square error: 0.4-1.3gCmday, revised Willmott index: 0.16-0.55). In particular, we demonstrated that the annual reservoir surface effluxes were initially high, steeply declined in the first three years, and then steadily decreased to ~115gCmyr with increasing reservoir age over the estimated "engineering" reservoir lifetime (i.e., 100years). Sensitivity analyses revealed that increasing air temperature stimulated CO emissions by enhancing CO production in the water column and sediment, and extending the duration of open water period over which emissions occur. Increasing the amount of terrestrial organic C flooded can enhance benthic CO fluxes and CO emissions from the reservoir water surface, but the effects were not significant over the simulation period. The model is useful for the understanding of the mechanism of C dynamics in reservoirs and could be used to assist the hydro-power industry and others interested in the role of boreal hydroelectric reservoirs as sources of greenhouse gas emissions.