Greenhouse Gas Emissions From a Large and Shallow Tropical African Lake: Contribution of Different Gases and Emission Pathways

Globally, nutrient enriched water bodies are major contributors to the aquatic greenhouse gases (GHG) efflux to atmosphere. However, few efforts have focused on assessing the contribution from coastal transitional ecosystems in Africa. To improve our knowledge of these systems, we investigated emissions in Lake Nokoué, a coastal lagoon in Benin (salinity range 0–27). CO 2 , CH 4 , and N 2 O were analyzed through ebullition and diffusion at river mouths (freshwater inlets to the lake), open waters (lake free water), and aquaculture sites over 9 months for different hydrologic seasons. The results indicate that river mouths were hotspots of both ebullition and diffusive fluxes. The total mean daily fluxes there, 12.8 ± 19.4 mmol m −2 d −1 for CH 4 , 224.7 ± 208.7 mmol m −2 d −1 for CO 2 , (4.5 ± 5.6) × 10 −3 mmol m −2 d −1 for N 2 O, were about 8, 4, 5 times higher than in the open water and represent efflux from water to atmosphere. However, on the whole lake scale, the aquaculture sites represented about the two thirds of the total annual emissions giving their large coverage on the lake ∼50%. Ebullition was revealed not to be the major emission route as it only represented 5.4% of the emissions. Following the seasons, diffusive CO 2 and N 2 O fluxes were significantly higher in the high‐water period than in the low water period. Overall, CO 2 (70%) was the most emitted gas followed by CH 4 (29.8%) in terms of CO2‐equivalents. This study advances our understanding of spatial and temporal greenhouse gas variability, emphasizing the role of river mouths in driving emissions.