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Scientific evidence is undeniable: aquifer exploitation is causing serious impacts on the most iconic national park in Spain

Aves descansando en la laguna de Santa Olalla. // Carlos Ruiz, EBD – CSIC

A scientific team from the Doñana Biological Station and the Geological and Mining Institute, institutes of the Spanish National Research Council, has reviewed more than 70 studies and demonstrates how scientists have been warning for years of the impact that groundwater abstraction causes in Doñana

A scientific team led by the Doñana Biological Station and the Geological and Mining Institute, of the Spanish National Research Council, has reviewed more than 70 studies related to groundwater and the conservation status of one of the Europe's most iconic wetland, Doñana, in southern Spain. The research has shown that there is ample scientific evidence of the serious impacts caused by groundwater abstraction. A total of 22 researchers from different institutes, both in the field of wetland ecology and hydrogeology, with extensive experience in research projects in Doñana, have participated in this study.

Data from the Confederación Hidrográfica del Guadalquivir (Guadalquivir River Basin Authority) show a general decline in water tables throughout the protected area over the last three decades, especially in the areas closest to where water is extracted for agricultural and urban use. In addition, numerous scientific studies have recorded impacts on the aquatic and terrestrial habitats of Doñana, as well as on water quality.

Since the 1970s different scientific and technical voices have reported that uncontrolled abstraction of groundwater would have very serious consequences for Doñana," says Carolina Guardiola Albert, CSIC researcher at the Geological Mining Institute. "It is inevitable to feel that water and land managers involved in this area at all scales have not heard these complaints, or if they have heard them, they have failed to take effective action," she continues.

Despite the scientific evidence, for years no measures have been implemented to successfully avoid, or at least mitigate, these impacts on the protected area. Given the inaction of the administrations in this regard, the Court of Justice of the European Union condemned Spain in 2021. A year later, European Union warned Spain again with a new judgment if an agreement was not reached soon to withdraw a proposed law, presented in the Andalusian regional parliament, that sought to expand irrigation in Doñana's surroundings. "The actions of the European Court of Justice brought about a change of attitude, but we remain skeptical that the necessary measures will be implemented and, above all, that all the administrations and agents involved will be able to coordinate to implement these measures effectively," explains the scientist.

Impacts on both aquatic and terrestrial habitats

Scientific evidence on the impacts that agriculture is causing on Doñana is clear and abundant. There are several studies that show how the reduction in groundwater levels has led to the disappearance of many ponds, key for the conservation of many species. In one of the studies reviewed, published in 2001, a drop in water table of up to 20 meters between 1972 and 1992 was detected. The researchers also noted the disappearance of ponds that had been recorded in historical maps, especially in the northern area, the most affected by groundwater declines, largely due to irrigation. More recently, in a study published last year, the Doñana Biological Station identified a loss of almost 60% of the ponds that existed in the 1980s. In addition, it was found that the most of the ponds flood less and dissecate earlier than expected based on climate, especially in the areas closest to Matalascañas and the greenhouses, which reveals the impact caused by the overexploitation of the aquifer. This affects numerous animal species that depend on the existence of water bodies in their reproductive season, as well as aquatic vegetation.

The extraction of water from the aquifer is also having strong impacts on the marsh. Along with rainfall, surface water streams into the marsh receive inputs from the aquifer. However, these have been reduced in recent years. Several studies conducted in the Rocina area in the early 2000s suggest a 60% reduction in groundwater discharges to the streams circulating through the area. This trend has been exacerbated by the large expansion of intensive agriculture in the area since then. In addition, the reduction in groundwater discharge explains changes in dominant species in riparian forests of this area, with a progressive decline in willows, which are more dependent on water, and an increase in ash trees, which are less dependent.

And it is not only affecting aquatic habitats. It has also had an impact on terrestrial vegetation. For example, cork oaks that are hundreds of years old are now dying quickly in Doñana. According to ICTS-RBD data, 8%  have already perished since 2009 and many are losing their leaf cover due to falling water tables. Many other changes in vegetation are being recorded. Species such as Erica scoparia, a type of heather, are being replaced by more drought tolerant species such as gorse Ulex australis. In addition, a recent study has recorded how pines and shrubs are colonizing the basins of many dry temporary ponds, which indicates wetland deterioration and disappearance.

Impacts on water quality

But groundwater-dependent agriculture is not only having serious impacts on terrestrial and aquatic biodiversity but also on water quality. "While we tend to think more about water quantity than water quality, the truth is that they are equally important," explains Andy J. Green, CSIC research professor at the Doñana Biological Station. "Nutrient and contaminant loads to the marsh have been increasing with agricultural and urban expansion, especially around El Rocío." These issues have long been of concern to the scientific community, and numerous studies on water quality have been carried out on both surface and ground water.

The impact on water quality is intimately connected to the use of agrochemicals for red fruit irrigated crops. A reduced flow rate leads to further increases in concentrations of contaminants, and increased salinity through higher evaporation rates. Climate change, with a strong increase in temperature, is favouring the proliferation of  toxic algae and invasive plants for this type of nutrients. For example, phosphorus loading has increased sharply since 2000, which has in turn favoured the expansion of the invasive aquatic fern Azolla filiculoides across the marsh and some ponds, negatively impacting amphibians and aquatic plants.

Recent data show extremely high nutrient loads in streams affected by groundwater pumping for agriculture. "We have transformed the National Park into a green filter to clean up stream water, which many times is already toxic for fish and other wildlife", says Andy J. Green. Pollution in the Doñana aquifer due to agricultural and urban activities dates back to initial expansion of irrigation in the 1970s and the deterioration of groundwater quality has been recognized by international institutions. "Measures are urgently needed to reduce the input of fertilizers into the aquifer and to clean the water before it enters the National Park," says the researcher.

One of the most often mentioned proposals when talking about implementing measures for the conservation of Doñana is to transfer water from other nearby watersheds. The scientific team considers, however, that this may be unrealistic given the limited volume of surface water available and climate model predictions for the southern Spain. Furthermore, the supply of surface water from other watersheds could facilitate biological invasions and promote further eutrophication associated with expansion of irrigated crops, as recorded in the Mar Menor wetland in south-eastern Spain.

"Thanks to the results of the scientific research carried out in Doñana, we can explain the relationship between the current state of the protected area, ascertained by the data collected, and the effects of external agents acting on it, such as the direct actions of human beings and the effects of climate change" explains Carolina Guardiola. "This knowledge is fundamental to guide decisions on measures to repair and prevent the state of the ecosystems."


Reference:

Andy J. Green, Carolina Guardiola-Albert ,Miguel Ángel Bravo-Utrera ,Javier Bustamante ,Antonio Camacho ,Carlos Camacho ,Eva Contreras-Arribas ,José L. Espinar ,Teresa Gil-Gil ,Iván Gómez-Mestre ,Javier Heredia-Díaz ,Claus Kohfahl ,Juan José Negro ,Manuel Olías ,Eloy Revilla ,Patricia M. Rodríguez-González ,Miguel Rodríguez-Rodríguez ,Fernando Ruíz-Bermudo ,Luis Santamaría ,Guido Schmidt ,José Antonio Serrano Reina &Ricardo Díaz-Delgado. Groundwater abstraction has caused extensive ecological damage to the Doñana World Heritage Site, Spain. Wetlands, 44, 20 (2024). https://doi.org/10.1007/s13157-023-01769-1

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