Limnetica 41

Freshwater reservoirs constitute a significant source of carbon dioxide (CO₂) and methane (CH₄) to the atmosphere, and a precise quantification of the magnitude of these greenhouse gas emission on an annual scale is required. This quantification must consider both temporal and spatial variability of reservoir carbon gas fluxes. In addition, it is relevant to reinforce re­search focusing on the emission of CO₂ and CH₄ in Mediterranean reservoirs. Here, we simultaneously measured CO₂ fluxes and CH₄ ebullitive and diffusive emissions in the riverine and lacustrine zones of a Mediterranean reservoir (El Gergal, Spain) throughout a complete year to quantify their magnitude, explore their spatial and temporal variability, and investigate the potential limnological and hydrological factors influencing gases emissions. Our results show that during the study year El Gergal riverine zone was a CO₂ sink, while the lacustrine zone was a CO₂ source. In addition, both areas were CH₄ sources to the atmosphere. CO₂ and CH₄ fluxes in El Gergal showed a marked temporal variability, with significant differences between mixing and thermally stratified periods. CO₂ emissions were significantly influenced by surface chlorophyll-a concentration and pH, suggesting the prevalent role of primary production as CO₂ flux driver. CH₄ emissions were influenced by hypolim­netic methane concentration and hydrological factors potentially affected by climate change, such as water renewal rate and water column depth.