Methane and carbon dioxide emissions from tropical reservoirs: Significance of downstream rivers

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Abstract
Methane (CH4) and carbon dioxide (CO2) concentrations and water‐air fluxes were measured in three tropical reservoirs and their respective rivers downstream of the dams. From reservoirs, CH4 and CO2 flux were in the range of 3 ± 2 and 254 ± 392 mmol.m−2.d−1, respectively. Rivers downstream of dams were significantly enriched in CH4 and CO2 originating from reservoir hypolimnions. From rivers, CH4 and CO2 flux were in the range of 60 ± 38 and 859 ± 400 mmol.m−2.d−1, respectively. Despite their relatively small surfaces, rivers downstream of dams accounted for a significant fraction (9–33% for CH4 and 7–25% for CO2) of the emissions across the reservoir surfaces classically taken into account for reservoirs. A significant fraction of CH4 appeared to degas at the vicinity of the dam (turbines and spillways), although it could not be quantified.