The research, published in the journal ‘Global Change Biology’, has, for the first time in Spain, used a floating platform equipped with eddy covariance technology to continuously measure the greenhouse gases emitted by a reservoir

Continental aquatic ecosystems, such as lakes and reservoirs, occupy a small proportion of the Earth’s surface, but play a significant role in the global carbon cycle. It is estimated that over 40 per cent of global methane emissions originate from these ecosystems. However, the true scale of these emissions remains uncertain, as most of the available data comes from one-off measurements taken at specific times and locations.

Research carried out by an interdisciplinary team from the Departments of Civil Engineering and Ecology at the University of Granada (UGR), which form part of the Unit of Excellence Modeling Nature, and involving, amongst others, researchers Isabel Reche Cañabate, Francisco Rueda Valdivia and Cintia L. Ramón, has helped to reduce this uncertainty. The study, published in the journal Global Change Biology, has employed a micrometeorological technique known as eddy covariance, which is capable of continuously measuring gas exchange between the water surface and the atmosphere over large areas.

To this end, the team installed a floating platform equipped with a measurement tower on the Cubillas reservoir. This infrastructure has made it possible, for the first time in Spain, to apply the eddy covariance technique from a floating platform to continuously monitor carbon dioxide and methane emissions in a reservoir. The observations, collected over two years under very different hydrological conditions, show that the reservoir acts as a constant source of both greenhouse gases. Continuous measurements made it possible to detect phenomena and variations that one-off sampling failed to identify, particularly in the case of methane, whose emissions can change abruptly over time. They also revealed daily fluctuations and emission episodes that go unnoticed with conventional sampling methods.

The results indicate that, whilst carbon dioxide emissions remained largely unchanged, methane emissions increased significantly during the driest years and when water reserves were declining. Lower water levels promote biogeochemical processes in the sediments that increase the production and release of this gas, particularly through bubbling phenomena. The study also notes that factors such as wind or eutrophication can influence the intensity of emissions.

The research highlights the importance of developing continuous monitoring systems to better understand how these ecosystems function and to improve our ability to predict their contribution to the global greenhouse gas balance. Furthermore, the findings can inform the design of more sustainable water resource management strategies in regions vulnerable to climate change.

Methane has a much higher global warming potential than carbon dioxide in the short term, making these findings particularly relevant in the context of climate change. According to the authors, the predicted increase in droughts and eutrophication processes could significantly boost methane emissions from Mediterranean reservoirs and reinforce their role as a source of greenhouse gases.