A quantication of photoproduction of CO2 throughout the water column by degradation of terrigenous organic compounds present in the dissolved form for aquatic ecosystems of the boreal region in Quebec

This study focuses on the quantity of CO2 produced by photodegradation in various pristine and disrupted water bodies. Photodegradation of dissolved organic matter (DOM) in the water column was evaluated in relation to two environmental factors e.g., the presence or absence of logging on the watershed and the contrast between natural lakes and hydroelectric reservoirs. Water samples were irradiated after filtration under 0,2µm, and subsequently analyzed for their CO2 production. Mean energy normalized for the spectral energy exposed to samples was determined to evaluate the photoreactivity of DOM under similar exposure conditions. In complement, organic matter samples had been concentrated via reverse osmosis. We then characterized the origin of DOM present in the water column with lignin biomarkers. Our results confirmed that the photomineralization increased significantly with DOM concentration. The daily photodegradation production was strikingly different in natural lakes and hydroelectric reservoirs. Average springtime and summertime production was evaluated at 5.45 ± 5.61 µmol.L-1.d-1 for lakes, compared to 14.21 ± 8.77 µmol.L-1.d-1 for boreal reservoirs. A similar comparison between ecosystems affected and unaffected by logging, also showed contrasting results for the photodegradation of DOM. Moreover, our lignin biomarkers increased significantly with CO2 generation. It thus appears that allochthonous organic matter strongly influences CO2 photoproduction. Finally, we evaluated the Photochemical Contribution to CO2 diffusive Fluxes (PCFCO2) between 14% and 32% depending on the degree of perturbation of the aquatic system.