To the Editor — It is widely appreciated that the world’s wetlands provide important ecosystem services including critical biodiversity, stores of carbon and strong cultural links to people. Yet wetlands are disappearing at an alarming rate due to diversion and abstraction of water, to conversion to agricultural land and to pollution. In response, there has been a major commitment to conserve and restore wetlands worldwide, including more than 2,400 sites on the territories of 172 Contracting Parties of the Convention on Wetlands (Ramsar Sites), covering more than 2.5 million square kilometres. Some wetlands, such as Doñana in southern Spain, are also World Heritage sites to protect their natural and cultural values. The Ramsar Convention and UNESCO World Heritage Convention strongly support the rights of non-governmental organizations to appraise the status and management of designated sites and welcome reports of threats to site integrity. However, such claims should be substantiated by all the available scientific evidence.
As highlighted in a recent Correspondence1, WWF Spain has publicised its concerns that groundwater abstraction for growing fruit (mainly strawberries) near to Doñana has lowered water table levels in the underlying aquifer and that this is posing a major threat to the wetlands2. In response, a team of experts was assembled by the UNESCO World Heritage Centre, IUCN (International Union for the Conservation of Nature) and the Convention on Wetlands (Ramsar) to assess the eco-hydrological situation in Doñana. In 2020 this team undertook a systematic review of the evidence to test the hypothesis that groundwater abstraction has degraded the wetland3. From sources such as Web of Science, Google Scholar and groundwater/wetland experts in Spain and worldwide, the team found 374 publications of relevance to the subject. Of these, 87 articles contained quantitative evidence from eco-hydrological studies. Analysis of this evidence revealed a complex story. First, Doñana is composed of a mosaic of wetlands that need to be considered, principally the seasonally flooded marshes (marismas), the dune ponds (lagunas) and the marginal ecotone freshwater habitats lying between the dunes and the marshes. Second, the groundwater system is formed of many aquifer units, including the many detritic aquifer units and the dune aquifer, some of which interact, while others are hydrologically separate. Third, the situation is rapidly changing as the Spanish authorities implement major abstraction management. The key findings of the review were as follows.
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1.
There was strong evidence from measurements that several detritic aquifer units underlying the fruit irrigation area, including La Rocina, Almonte and Marismas, have experienced significant declines in water table level, and the Spanish authorities have declared that they are at risk of failing to achieve Good Status under the European Water Framework Directive. In response, the Spanish government has purchased some water rights and illegal wells are being closed, though achieving sustainable abstraction may take 7 years.
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2.
There was strong evidence from measurements that in some aquifer units, water levels have remained fairly constant over the past 27 years, with only slight fluctuations caused by variations in rainfall.
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3.
There was strong evidence from measurements that water levels in the dune aquifer were lower in locations adjacent to abstraction wells supplying the town of Matalascañas, but this abstraction is due to be ceased.
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4.
There was some evidence from hydro-geological modelling of minor interactions between the detritic and dune aquifers at specific locations, but the full extent of aquifer connectivity was uncertain.
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5.
There was no evidence that the decline in water table levels in the detritic aquifer units caused by groundwater abstraction has affected the marshes (Fig. 1).
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6.
There was inconclusive anecdotal evidence that groundwater abstraction from the main exploited detritic aquifer units has affected small ecotones around the marshes.
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7.
There was strong evidence from measurements that abstraction from the dune aquifer had altered some dune ponds close to the wells, but that others distant from the abstractions were not affected.
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8.
There was evidence from atmospheric modelling that climate change could alter the hydrology and ecology of the site in the future.
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