Insights on riverine metabolism from continuous measurements of CDOM fluorescence in Eastmain-1 Reservoir, Quebec

Rivers are notorious1y variab1e. In contrast to 1akes where factors influencing the metabolic ba1ance of the ecosystem are fairly well constrained, rivers are typically more difficu1t to predict and genera1ize. In 1acustrine systems, the interp1ay between externa1 organic carbon 1oads and in-1ake metabo1ic processes (primary production, sediment accumu1ation, pe1agic and benthic respiration) is key to determining the net status of these systems, and simp1e ru1es app1y generally. For examp1e, in temperate and borea1 1akes, an upper thresho1d va1ue of5-6 mg L-1 DOC often constitutes the average concentration for net heterotrophic 1akes (HANSON et al. 2003). Surprising1y, this thresho1d is not very sensitive to the trophic status oflakes (PRAIRIE 2008). This dominance of respiration over primary production 1eads to co2 supersaturation and thus evasion to the atmosphere, a phenomenon observed in the majority of aquatic systems (COLE et al. 1994, DuARTE & PRAIRIE 2005).