The number of reservoirs is in expansion due to population growth, linked to an increase in water and energy demand. Besides that, climate change and direct anthropogenic pressures trigger alterations in hydrology and thermal structure which could modify carbon fluxes and water quality in these ecosystems. This study tackles the effect of hydrological and thermal structure changes in carbon fluxes in a Mediterranean reservoir (El Gergal, Spain) measuring CO₂ and CH₄ fluxes from water surface, CO₂ fluxes from drawdown areas and the accumulation of CO₂ and CH₄ in the hypolimnion. The results showed that hydrology and thermal structure have an impact on carbon fluxes in the reservoir affecting CO₂ and CH₄ fluxes. During stratification, water level is lower, increasing drawdown areas and, therefore, rising CO₂ emissions from these surfaces. In addition, stratification and lower water renewal enhance anoxia in the bottom of the reservoir promoting anaerobic respiration of organic matter. This leads to higher production of CH4 that together with lower water level will increase diffusive and ebullitive fluxes of CH₄. Furthermore, anaerobic processes produce reduced substances (e.g. HS^-), impairing water quality, and accumulate CO₂ and CH₄ in the hypolimnion that could be released to the atmosphere during fall turnover. These results suggest that longer stratification periods with more frequent and intense droughts, which lead to low water episodes with higher residence time and higher risk of anoxia, will impair water quality and enhance the carbon emissions of reservoirs.

Primary Presenter: Jorge Montes-Pérez, University of Malaga (jmontesp@uma.es)

Authors:

Jorge Montes-Pérez, University of Malaga  (jmontesp@uma.es)

Rafael Marcé, Catalan Institute for Water Research ICRA  (rmarce@icra.cat)

Carmelo Escot, Empresa metropolitana de abastecimiento y saneamiento de aguas de Sevilla (EMASESA)  (CEscot@emasesa.com)

Isabel Reyes,  Empresa metropolitana de abastecimiento y saneamiento de aguas de Sevilla (EMASESA)  (eIRBarbara@emasesa.com)

Enrique Moreno-Ostos, University of Malaga  (quique@uma.es)