This time it was not in August, but at the beginning of October, and the fact that it was repeated, far from giving it normality, makes this circumstance much more alarming. For the third consecutive year, the Santa Olalla lagoon, the largest in the Doñana natural area, has dried up, as already happened in the summers of 2022 and 2023. This situation has never occurred before, since the Doñana Biological Station, dependent on the CSIC, began collecting data half a century ago. “The combination of an intense and prolonged drought and the overexploitation of the aquifer is having a great effect on the lagoon system of the protected area,” explains its director, Eloy Revilla.
Those responsible for the Biological Station warn of the “critical situation” of the Santa Olalla lagoon, under which there is only a superficial sheet of residual wetland and mud that makes it impossible to take any representative water sample. Until three years ago, this lagoon was almost the only one of the more than 3,000 that Doñana has that used to hold water. The summer of 2022 broke with this trend, which was repeated in 2023. “The hydrological cycle that has just closed, that of 2023-2024, therefore began with a completely dry Santa Olalla,” explains Javier Bustamante, researcher at the EBD.
The rains last October helped the level of the aquifer to rise, a situation that, however, only lasted until February. The high temperatures detected since April not only reduce the level of accumulated water, but also favor the proliferation of filamentous algae around the shore of the lagoons, increasing the toxicity on other species such as birds or fish. Heat also causes an increase in phytoplankton and salinity levels in the water.
Santa Olalla is not only drying up, but it has been gradually losing its former extension. “Aerial images show that its current shores and its central island are being invaded by tamama trees and other types of terrestrial vegetation,” says Bustamante. This lagoon is not the only one that has dried up this year, the neighboring Dulce lagoon has also dried up completely during the second week of September. This is another space that has also stopped being considered a permanent lagoon, because last year it also ran out of water at the beginning of August.
A “change without return”
As has happened with 60% of the lagoons that existed in Doñana in the eighties, which have already disappeared. The remaining 40% that remain, however, flood less and less and do so for a much shorter period than expected by the climate. Scientists at the Biological Station recognize that this situation is getting worse due to the drought that has plagued this natural reserve in the last decade, with below-average rainfall, but, even so, the change in the dynamics of the lagoons also It is highly conditioned by direct human action, which is interfering with its natural cycle, warns the CSIC.
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“This was confirmed when it was observed that this phenomenon [la menor inundación durante menos tiempo] “It most affected the lagoons closest to the intensively irrigated crops and the tourist town of Matalascañas,” says Revilla, who also warns of how the majority of the lagoons that still exist are being colonized by terrestrial vegetation, “which indicates a change without return”.
“An international report from WWF already warned in the late 80s of the effects on the lagoons near Matalascañas and then the wet periods were longer and it rained more, so it is clear that the situation cannot be attributed to climate change or drought, These are factors that accentuate a problem caused by the agricultural exploitation model,” supports Juanjo Carmona, head of the NGO in Doñana. “All administrations know the problem and know what the future of the Park will be if overexploitation continues, but they do not dare to stand up to the productive fabric or the social mass. It is not enough to close wells, what is needed is to bring surface water from the Tinto, Odiel and Piedra basin, but for the conservation of the wetland, which is public interest, not for agriculture,” Juan Romero points out as solutions from Ecologists in Action.
Several studies by the Biological Station confirm the great impact that the deterioration of the Doñana lagoon system is having on the fauna and flora. The CSIC draws attention to the populations of the two native turtles, the European and the leper, which are about to disappear, or to the reduction of the 11 amphibian species, whose presence has been monitored for almost 20 years.
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