Underground water reserves at risk due to climate change – according to study


Caldas da Rainha, Leiria, 30 Nov 2023 (Lusa) – Climate change could compromise the quality of existing strategic water reserves in underground ecosystems, concludes a study in 12 caves across the globe, coordinated by Portuguese scientist Ana Sofia Reboleira.

The study, published on Saturday in the scientific journal Scientific Reports, from the Nature group, analysed “an unprecedented set of data” collected over a year in caves in various parts of the globe, from subarctic to tropical regions, including in Portugal, caves in the centre of the country, in the Algarve and the Azores.

Over the course of a year, the temperature in caves and on the surface was measured every two hours, totalling more than 100,000 measurements, which “demonstrate that the temperature in the caves corresponds to the average annual surface temperature for each location”, said Ana Sofia Reboleira, Professor at the Faculty of Sciences of the University of Lisbon and researcher at the Centre for Ecology, Evolution and Environmental Changes, to the Lusa agency.

According to the biologist “the caves responded with three different patterns”: one in which the variation in outside temperature is reflected in the cave with a small delay, another in which the temperatures on the surface are quickly reflected inside and, a third in which they work in mirror, the lower the surface temperature, the higher inside the cave and vice versa.

More surprising was the discovery of the “existence of daily thermal cycles in some caves”, considered by the researcher “particularly interesting because in ecosystems with a total absence of light, organisms lack circadian rhythms, that is, biological rhythms marked by the natural cadence of day and night controlled by sunlight at the surface.”

This discovery “shows that these daily thermal cycles can potentially control the biological rhythms of underground organisms”, a hypothesis that is proposed for the first time in the history of Biology.

“These ecosystems are inhabited by unique species that play a very important role in what scientists call ecosystem services” since, she explained, “it is these animals that guarantee the recycling of nutrients in depth, of some contaminants that arrive there, which control bacterial growth and other types of problems that can affect us.”

In the case of organisms adapted to low amplitudes and reduced thermal variability, the increase in temperatures by several degrees, due to climate change, “will certainly affect these organisms responsible for guaranteeing the good ecological status of these underground water bodies”, which represent 97% of total freshwater resources available for immediate human consumption.

Among the caves covered in the study, the scientist highlights the case of one in Loulé that recorded the highest surface temperature, with more than 39 degrees, and another in the Azores, with the greatest thermal amplitude, with a variation of 8.8C, explained by the fact that it is a volcanic cave.

The impact of climate change, combined with the fact that underground ecosystems “are constantly neglected in political and public agendas”, lead researchers to now move forward with laboratory studies “on the effects of rising temperatures on these organisms” aiming to estimate the maximum temperatures that these will be able to handle it.

The study now published included, in addition to the coordinator, the participation of Maria João Medina, a master’s student whose dissertation included the study, and Paulo Borges from the University of the Azores. At an international level, the work involved researchers from the United States, Serbia, Slovenia, Norway, Spain (including the Canary Islands), Croatia and the island of Guam, in the Pacific.