RESEARCH ARTICLE The UNESCO national biosphere reserve (Marismas del Odiel, SW Spain): an area of 18,875 ha affected by mining waste Jose M. Davila 1,2 & Aguasanta M. Sarmiento 1,2 & Maria Santisteban 1,2 & Ana T. Luís 1,5 & Juan C. Fortes 1,2 & Jesus Diaz-Curiel 3 & Catherine Valbuena 4 & Jose A. Grande 1,2 Received: 26 April 2019 /Accepted: 5 September 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract At the mouth of the Odiel River, within the Natural Area “Marismas del Odiel”, there has been for years a collection of waste from different mining sites. In the present work, an approach has been made to the problem that this supposes, quantifying the pollutants that are poured into the estuary from the mineral collection located on the banks of the river. The study carried out has been able to determine high metal concentrations, comparable with any rubble from the upstream mines, with pH value of 1.66, lower than many other areas affected by acid mine drainage in the same river, and even with concentrations of Fe and As higher than those provided by the rest of the mining facilities of the Odiel basin. This can make us understand the serious situation of the Natural Park, where a great variety of birds and plants of special ecological interest are located. Keywords Acid mine drainage . Biosphere reserve . Estuary . Metal pollution . Water quality . Odiel Introduction Acid mine drainage process The process of extracting iron sulphide ores (the most common is pyrite—FeS 2 ) involves a type of hydrogeochemical contamina- tion known as acid mine drainage (AMD). This process appears when pyrite is combined with oxygen in the presence of humid- ity, which in turn produces a reduction in the pH value of the water, reaching values close to 2, an increase in the concentration of sulphate and an increase in the content of heavy metals and other harmful elements (Lyew and Sheppard 2001; Grande et al. 2005a; de la Torre et al. 2010). The production of acid leachate takes place in two phases (Grande 2016): one of short duration due to rapid runoff, followed by another of variable duration due to slow runoff. Depending on the hydrological regime and the timing of rain- fall, one phase or another will be more relevant. Thus, we can affirm that the pollution produced by leachate is the result of the combined action of a mechanism generating pollutants and another responsible for transporting them to the outside of the dump or mineral stockpile (Sáinz et al. 2002). The reactions that occur from the oxidation of pyrite (FeS 2 ) were explained by Singer and Stumm (1970) and Nordstrom and Alpers (1999): FeS 2 þ 7=2O 2 þ H 2 O→Fe 2þ þ 2SO 4 2− þ 2H þ ð1Þ If these reactions take place in a sufficiently oxidizing en- vironment, many of the ferrous ions will change to ferric ions, a process in which acidity is consumed (Eq. 2) Fe 2þ þ 1=4O 2 þ H þ →Fe 3þ þ 1=2H 2 O ð2Þ Responsible editor: Philippe Garrigues * Jose M. Davila jmdavila@dimme.uhu.es 1 Department of Water, Mining and Environment, Scientific and Technological Center of Huelva, University of Huelva, 21004 Huelva, Spain 2 Sustainable Mining Engineering Research Group, Department of Mining, Mechanic, Energetic and Construction Engineering, Higher Technical School of Engineering, University of Huelva, 21007 Huelva, Spain 3 Escuela Técnica Superior de Ingenieros de Minas, Ríos Rosas 21, Madrid, Spain 4 Department of Mining, Mechanic, Energetic and Construction Engineering, Higher Technical School of Engineering, University of Huelva, 21007 Huelva, Spain 5 Department of Geosciences, Campus de Santiago, GeoBioTec Research Unit, University of Aveiro, 3810-193 Aveiro, Portugal Environmental Science and Pollution Research https://doi.org/10.1007/s11356-019-06438-7