Understanding the emission of greenhouse gases in reservoirs under the inspiration of Margalef

Resum

Reservoirs are significant sources of greenhouse gases as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) to the atmosphere. These systems receive and metabolize a larger amount of organic and inorganic carbon, and nitrogen from their watersheds than lakes, resulting in the production of CO₂, CH₄ and N₂O. Despite their global relevance, there are still important uncertainties regarding the magnitude, variability and the drivers of their emissions that undermine global estimates. Therefore, a comprehensive understanding of the origin of these emissions is required. Here, I study the fluxes of CO₂, CH₄ and N₂O and their concentrations in the water column of twelve Mediterranean reservoirs during the stratification and mixing periods to discuss the main pathways involved in their production and the inter-gas, spatial, and seasonal variability of these emissions and their radiative forcing. Finally, I provide a theorical framework to understand greenhouse gas emissions as a response of reservoirs to eutrophication and external forcing. I bring up Margalef’s ideas and integrate them with the main findings of my previous work to analyze how the C, N and P inputs from reservoir watersheds modify the biogeochemical cycling of C, N, P and O, and determine the production and emission of CO₂, CH₄, and N₂O. This is especially notably for CH₄, and N₂O emissions, which increase significantly in eutrophic waters, even exceeding the climate forcing of CO₂. Therefore, emission of greenhouse gases should be seen as part of the reservoir response to external forcing, that displace a fraction of the materials to the atmospheric boundary.