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

Methane (CH 4 ) and carbon dioxide (CO 2 ) concentrations and water‐air fluxes were measured in three tropical reservoirs and their respective rivers downstream of the dams. From reservoirs, CH 4 and CO 2 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 CH 4 and CO 2 originating from reservoir hypolimnions. From rivers, CH 4 and CO 2 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 CH 4 and 7–25% for CO 2 ) of the emissions across the reservoir surfaces classically taken into account for reservoirs. A significant fraction of CH 4 appeared to degas at the vicinity of the dam (turbines and spillways), although it could not be quantified.