Doñana, listed as a world heritage site by UNESCO, is a complex natural space whose backbone is water. The hydrological system of the park is subject to permanent controls and constant surveillance. But this ecosystem cannot be analyzed only in a singular area because the wetland supply network extends beyond the protected area. An investigation, published in Wetlands Ecology and Management and led by Irene Paredes, from the Department of Wetland Ecology of the Biological Station of Doñana (CSIC), has detected high levels of water contamination in streams that supply the reserve due to excesses of concentration of nutrients (eutrophication), a phenomenon that has put other natural spaces in check and that threatens this biosphere reserve. "In some sections, the contamination thresholds compatible with life are exceeded if they are prolonged in time", warns the researcher.
The research has analyzed water quality parameters (nitrogen, phosphorus, chlorophyll-a of phytoplankton, conductivity, depth, and flow rate) at 56 points over three years. To this information, satellite data have been added on the growth of the surface of agricultural greenhouses that show an extraordinary result: the area covered by crops under plastic in the basins that discharge into the Doñana marsh has grown by 487% since 1995.
The area covered by crops under plastic in the basins that discharge into the Doñana marsh has grown by 487% since 1995
The relationship of both elements, pollution and greenhouses, is relevant because the origin of the negative evolution of the quality of water resources is in the wastewater of the permanent and temporary populations of the area (more than 10,000 people eventually work in the surrounding crops) and intensive agricultural activity. “The first cause”, as Paredes explains, “is easier to detect and correct, but the one generated by the impact of agriculture is more difficult to control and is more diffuse.”
Paredes explains how excess pollution is generated: “Runoff [rainwater that circulates over land or overflows natural or artificial channels] carries fertilizers and phytosanitary products into streams or infiltrates into groundwater. Natural biological, geological and chemical processes stop part of this pollution, but if the growth of agricultural activity is not stopped and the growth of agricultural activity is maintained, it will reach the park. The water entry zones in the marsh already reflect this. ”
The pressure of intensive agriculture continues and, according to researcher Irene Paredes, "what there is is already too much"
The situation is more worrying for two reasons, according to the study: the first is that the pressure of intensive agriculture continues and, according to the researcher, "what is already there is too much"; The second reason is that the situation is generated in the basins that discharge into the park, but are outside the protected area, so they are excluded from the reserve's control measures
Researcher Irene Paredes takes samples of water from the marsh of Doñana during the investigation.CSIC
Of all the points analyzed during the investigation, Rocina and Partido, one of the main tributaries to the marsh and subjected to great agricultural and human pressure, showed the highest values of nutrient concentrations. In some sections, the thresholds compatible with the survival of flora and fauna and the limits allowed by the European water directive were exceeded, according to the study.
In some sections, the thresholds compatible with the survival of flora and fauna and the limits allowed by the European water directive were exceeded, according to the study
But this contamination, in addition to ruining natural ecosystems due to the uncontrolled proliferation of microorganisms, also favors the expansion of invasive plants, such as the Arzolla filiculoides fern, which occupies the spaces of other native species.
For the researcher, the solution has to combine “palliative and preventive measures”. In this sense, it advocates the coordination of the management of the entire area, beyond the protected areas, and the change of the model of exploitation of the environment, "with alternatives that can be lived on." In the short term, it is possible to establish green filters that contain contamination by nutrients and establish formulas for the preservation of the areas where it is generated.
An update of agricultural drainage systems and other practices, such as the implementation of denitrification zones, would reduce nitrate loads by between 25% and 78%
This problem, especially critical in areas as sensitive as Doñana, is global. Some research attempts to address the conflict. According to a study published in Nature Sustainability , an update of agricultural drainage systems and other practices, such as the implementation of denitrification zones, would reduce nitrate loads by between 25% and 78%. For Sotirios Archontoulis, professor of agronomy and co-author of the study, “The improvement in the drainage systems would increase the yield of crops and the efficiency in the use of nitrogen fertilizers.”
Miguel Ángel Bravo, one of the researchers of the study together Irene Paredes, Francisco Ramírez, David Aragonés, Manuela G. Forero and Andy J. Green, took samples of the water from the El Rocío treatment plant. CSIC
Other studies point in the direction of spatial management of agricultural areas, limiting the intensive production where biodiversity is most threatened. A study published in Global Change Biology highlights how “increased agricultural production generally has negative side effects on agricultural landscapes, wildlife and ecosystem functions. In this sense, the study considers that concentrating agricultural growth in areas where less biodiversity is threatened, as well as interconnecting habitats through natural corridors, would allow the preservation of 88% of it.
formulas are also being investigated to maintain productivity and quality with the least possible impact. In this sense, a team from the University of Seville has isolated, identified and characterized up to 150 strains of beneficial bacteria, with the ability to promote crop growth, nitrogen fixation and protection against pathogens.
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