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Accueil du site → Doctorat → Espagne → 2014 → Natural and Induced Nitrate Attenuation Processes in Pétrola Basin (Albacete, Spain)

Universitat de Barcelona (2014)

Natural and Induced Nitrate Attenuation Processes in Pétrola Basin (Albacete, Spain)

Carrey Labarta, Raúl

Titre : Natural and Induced Nitrate Attenuation Processes in Pétrola Basin (Albacete, Spain)

Auteur : Carrey Labarta, Raúl

Université de soutenance : Universitat de Barcelona

Grade : Tesis Doctoral 2014

Résumé partiel
One of the main problems of diffused groundwater contamination is produced by nitrate (NO3‾). NO3‾ pollution is linked with fertilizer application, manure management and wastewater. Many areas of Spain have NO3‾ concentration over the human consumption (0.8 mM NO3‾) established by the Directive 98/83/CE. Endorheic basins located in semiarid or arid regions constitute one of the most vulnerable environments to NO3‾ pollution. The Petrola basin (Central Spain) is an outstanding example of these endorheic systems. Nitrate concentration in surface and groundwater from Petrola basin ranged from <1.6x10-3 mM to 2.5 mM. The observed variation in NO3‾ concentration could be linked with naturalattenuation. In this basin two different sediments are able to produce denitrification : 1) the organic and sulphide-rich sediment from the Utrillas Facies (Lower Cretaceous) and 2) the bottom lake sediment. Laboratory experiments coupled with field data can be applied to improve the understanding of the nitrogen cycle in Petrola basin. The study of Cretaceous Utrillas Facies and bottom lake sediments in laboratory experiments combining multi-isotopic techniques and chemical data showed that natural attenuation produced by both materials was mainly linked with the oxidation of the organic matter. In the case of Utrillas Facies, isotopic values of δ34SSO4 and δ18OSO4 ruled out pyrite as electron donor. Bottom lake sediments showed higher potential to remove NO3‾ than the Utrillas Facies. Important differences between both sediments were observed in the amount of reactive organic carbon, and in the nitrogen reduction rate. These differences were linked to the variation in the reactivity of the different organic carbon sources. Despite the remarkable differences, similar isotopic fractionation of N and O during denitrification for the Utrillas Facies and the bottom lake sediment were observed. The Utrillas Facies displayed values of ‾11.6‰ and ‾15.7‰ for εN and ‾12.1‰ and ‾13.8‰ for εO whereas denitrification produced by the bottom lake sediments showed εN of ‾14.7‰ and εO of ‾14.5‰. The hydrogeological study showed that groundwater flow in the Petrola basin can be considered as the result of two main flow components : a regional groundwater flow, from the recharge areas (Zone 1) to the discharge ones located near the lake (Zone 2) and the density driven flow from surface water from the lake towards the underlying aquifer (Zone 3). Isotopic results from the field showed that denitrification was taking place in the basin although it was restricted to the surrounding area (Zone 2) and under the lake (Zone 3). In addition, the using the isotopic fractionations obtained in the laboratory experiments, the percentage of NO3 ‾ attenuation was calculated. NO3‾ removed ranged from 0% to 60% with an average percentage of 20%. The degree of denitrification observed at field scale showed an important spatial variability related with the amount, availability and reactivity of labile organic matter as well as spatial variation of NO3‾ supply. Attenuation processes by heterotrophic denitrification reactions were more likely to occur in zones of the saline lake-aquifer system. Density downflow from surface water effectively transported the DOC to aquifer zones under reducing conditions ; however, its influence decreased with depth becoming negligible in the deepest part of the aquifer. As consequence of the incomplete NO3‾ attenuation observed in groundwater of Petrola basin a biostimulation treatment was proposed.

Mots Clés : Geologia isotòpica ; Isotope geology ; Hidrogeologia ; Hydrogeology  ; Desnitrificació ; Denitrification ; Cinètica química ; Chemical kinetic ; Bioestimulació  ; Bioestimulación ; Biostimulation

Présentation (TDX) -> http://www.tdx.cat/handle/10803/145971

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Page publiée le 16 novembre 2015, mise à jour le 13 février 2019