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Groundwater abstraction is among the main anthropogenic causes of wetland desiccation worldwide, and corrective measures must be taken to avoid degradation of this valuable ecosystems. A case study is the Agua Amarga salt marsh (≈180 ha) (SE Spain). Agua Amarga includes a solar saltwork pond network in operation between 1925 and 1975, when it was abandoned, and the ponds were colonized by salt marsh vegetation. In 2008 two desalination plants were operating in the marsh vicinity, which were supplied with groundwater. To mitigate the possible negative impact on the salt marsh ecosystem due to groundwater drawdown, in 2009 a sea water irrigation program was implemented. This paper summarizes the results of a ten-year monitoring program (2010–2020) to evaluate the effects of the irrigation program on groundwater levels and quality, soil salinity and moisture, and vegetation cover. During this period, average groundwater level was 2.5 m below the surface and around 1 m deep near the irrigated ponds. Groundwater salinity was not affected outside the saltmarsh, but inside, where the saltworks caused values to rise above 300 mS/cm, it decreased more than 150 mS/cm in some 20 m deep piezometers. Between 2012 and 2020, vegetation cover increased between ≈10 and ≈25 %, with halophyte species such as Arthrocnemum macrostachyum and Sarcocornia fruticosa being the most favoured. In areas with prolonged flooding, Ruppia maritima, a plant species that lives submerged in saline water, was found. In the irrigated areas, soil electrical conductivity (1:5 soil:water extracts) decreased from ≈7-14 mS cm-1 to ≈2-6 mS cm-1. We present an example of sustainable actions in a coastal wetland, where the exploitation of water resources in semiarid areas is combined with promoting natural habitats. Financial support for this research was provided by Mancomunidad de los Canales del Taibilla (http://www.mct.es). M.N. González-Alcaraz holds a Ramón y Cajal research contract from the Spanish Ministry of Science and Innovation (RYC2020-029322-I). We much appreciate the help of M. Carmen Tercero, Héctor M. Conesa and B. Aránega, from Technical University of Cartagena, and Francisco J. Jiménez-Cárceles, from Biocyma environmental consulting, during field and laboratory work. We thank to the technicians of the SAIT-UPCT for their laboratory and analytical assessments. Finally, we want to give special recognition to Doctor Tomás Rodríguez Estrella for his contributions in the field of hydrogeology.

[SPA] Los depósitos de minería metálica presentan condiciones desfavorables que dificultan la funcionalidad del suelo y la colonización vegetal. El objetivo de este trabajo fue evaluar si la adicción de enmiendas orgánicas (compost de residuos sólidos urbanos + biochar de restos de podas) mejora la funcionalidad de suelos desnudos de un depósito bajo clima Mediterráneo y si favorece la colonización espontánea de la vegetación. Se evaluaron diversos parámetros estacionalmente durante un año tras la adición de las enmiendas (p.e. pH; salinidad; carbono orgánico soluble; metales solubles; carbono de la biomasa microbiana y descomposición de la materia orgánica) La adición de enmiendas orgánicas mejoro las condiciones del suelo. Esto mejoró la funcionalidad microbiana del suelo, que persistió estacionalmente, y favoreció la colonización espontánea de la vegetación. [ENG] Metallic mine tailings present unfavorable soil conditions that hinder soil functionality and plant colonization. The aim of this study was to asses if the addition of organic amendments (compost of urban solid waste + biochar from pruning trees) improved the functionality of bare tailing soils under Mediterranean climate and favored spontaneous plant colonization. A series of soil parameters were seasonally evaluated after organic amendments addition during one year (e.g., pH, salinity, soluble organic carbon, soluble metals, carbon from microbial biomass and decomposition of organic matter). Organic amendments addition improved soil conditions. This enhanced soil microbial functionality, which persisted seasonally, and favored spontaneous plant colonization. Trabajo financiado por el Ministerio de Economía y Competitividad de España a través de fondos FEDER (Proyecto RESCLICONT- CGL2016-80981-R).

Las balsas de lodos de flotación, resultado de la actividad minera en la Sierra de Cartagena‐La Unión, suponen un riesgo de contaminación para el entorno y los seres humanos debido a las elevadas concentraciones de metal(oid)es que contienen. Las técnicas de ‘fitoestabilización’ aparecen como una alternativa viable a las técnicas convencionales de recuperación de suelos contaminados. El objetivo de este estudio fue describir los gradientes edáficos y microbiológicos presentes en una balsa minera abandonada de la Sierra de Cartagena‐La Unión, con el fin de plantear medidas para su fitoestabilización. Para ello, se realizó un muestreo de suelo a lo largo de un transecto desde una zona no contaminada hasta el interior de la meseta de la balsa. Los principales parámetros que determinaron inicialmente la distribución de la vegetación espontánea en la balsa fueron la conductividad eléctrica y el pH, mientras que la concentración de metal(oid)es jugó un papel secundario. Este proyecto ha sido financiado por el Ministerio de Economía y Competitividad y FEDER (CTM2011‐23958) y la Fundación Séneca de la Región de Murcia (15296/PI/10). El Doctor Héctor M. Conesa agradece al Ministerio de Economía y Competitividad y a la Universidad Politécnica de Cartagena por la financiación a través del Programa Ramón y Cajal (Ref. RYC‐ 2010‐05665). María Nazaret González‐Alcaraz disfruta de una beca post‐doctoral de la Fundación Ramón Areces.

[SPA] El Máster de Técnicas Avanzadas en Investigación y Desarrollo Agrario y Alimentario, tiene como principal objetivo la formación de investigadores en el ámbito del desarrollo agrario y alimentario, pues todos los indicadores actuales muestran que es necesario un aumento de la masa crítica de investigadores en éste área en la UE; a pesar de que la agricultura, desde la fase de producción hasta la de procesado y fabricación tiene un campo muy amplio en el que se puede investigar e innovar, existen determinadas herramientas horizontales de trabajo que permiten formar alumnos con unas capacidades técnicas excelentes y de aplicación a ámbitos tan variados como el medio ambiente, genética y mejora animal y vegetal, procesado de alimentos o control de las plagas. Estos antecedentes nos han llevado a formular un programa de Máster que tiene cuatro módulos definidos, uno de cursos metodológicos y tres de cursos fundamentales. [ENG] The Master in Advanced Techniques in Agricultural and Food Research and Development intends to introduce university students into the research in such field. The programme is based on research carried out by the Higher Technical School of Agriculture Engineer on the one hand, and on the other hand on the technological development of the Spanish agricultural and food sector. This Master programme has as its main goal the qualifying of researchers in the area of agricultural and food development, since all the present indicators point at the need for an increase in the critical mass of researchers in this area in the EU; despite the fact that agriculture, from production to processing and manufacturing, is a wide field in which to research and innovate. There exist some horizontal tools that allow us to train students with excellent technical skills, and that can be applied to a wide range of areas such as environment, genetics, animal and vegetal improvement, food processing or pest control. On these grounds we have been led to draw up a Master programme that has four clearly defined modules: one with methodology courses and three with basic courses. The students who follow the proposed Master programme should become university experts in research and development in the agricultural and food field. [ENG] The Master in Advanced Techniques in Agricultural and Food Research and Development intends to introduce university students into the research in such field. The programme is based on research carried out by the Higher Technical School of Agriculture Engineer on the one hand, and on the other hand on the technological development of the Spanish agricultural and food sector. This Master programme has as its main goal the qualifying of researchers in the area of agricultural and food development, since all the present indicators point at the need for an increase in the critical mass of researchers in this area in the EU; despite the fact that agriculture, from production to processing and manufacturing, is a wide field in which to research and innovate. There exist some horizontal tools that allow us to train students with excellent technical skills, and that can be applied to a wide range of areas such as environment, genetics, animal and vegetal improvement, food processing or pest control. On these grounds we have been led to draw up a Master programme that has four clearly defined modules: one with methodology courses and three with basic courses. The students who follow the proposed Master programme should become university experts in research and development in the agricultural and food field. Máster TAIDA

A reduction in plant cover can lead to an increase in the erosionprocesses that diminish soil quality. Any rise in temperature resulting frompredicted climate changes may aggravate this effect, particularly in semiaridMediterranean areas. Bearing this in mind, the capacity of a soil to preserveorganic matter becomes very important if the soil is to maintain its physicaland chemical properties. Soil organic carbon and nitrogen changes wereevaluatedin a non-disturbed (with natural vegetation) and a disturbed (all vegetationmanually clipped to ground level) pine system. Nine years after vegetationremoval significant differences (p < 0.01) were found in the soil organiccarbon content between plots (top 20 cm), but not in totalnitrogen. In the disturbed plot 0.0232 Mg ha–1y–1 of soil organic carbon were lost through erosionand4.30 Mg ha–1 y–1 throughmineralization. In the first 48 months after vegetation removal the soilorganiccarbon content fell from 40.3 to 28.0 g kg–1. Inthe last 60 months of the experiment the amount of organic carbon in the soilfell from 28.0 to 27.7 g kg–1. This result wasmainly attributable to the intense oxidization, which took place during thefirst 60 months, of organic matter linked to the coarse soil mineral fraction.Up to the 72nd month the losses by erosion were a total of 532.7g, which rose to 1284.4 g by the end of theexperiment(108 months). The effect of vegetation removal in a Mediterranean semiarid arealeads to a rapid decline in the amount of organic carbon stored in the soil.Such perturbation is irreversible if left to nature., This research was supported with funds from the Commission of the European Communities, EC Contract No ENV4-CT97-0687 MWISED. The experimental plots are included in the RESEL Network, Spain (Red de Estaciones de Seguimiento y Evaluación de la Erosión Hídrica en el Proyecto LUCDEME).

The vulnerability of Mediterranean arid and semiarid lands to human-induced changes in soil use means that the effects of climate change upon these environments will be exacerbated (Scharpen seel & Pfeiffer, 1998). Reduced precipitation or increased temperature accelerates l and degradation through the loss of plant cover, biomass turn over, nutrient cycling and soil organic carbon storage, accompanied by higher greenhouse emisions (Ojima et al.,1995). Moreover, if the projected increase in temperature following global climte change occurs, the degradative processes Will be aggravated (Kimble et al., 1998). Long term data series from natural rainfall events in semiarid environmnts are crucial for studying nutrient dynamics because: i) the soil's response within a few months of vegetation removal may not be sufficient for estimating its long-term behavior; and i i) it is difficult to produce data comparable to natural storms using rainfall simulators (Flanagan & Foster ,1989). The poster reports data obtained over a nine-year period (1988-1998) concerning changes in soil and sediment organic carbon and nitrogen contents in a non-disturbed vegetated area and an area from which vegetation had been removed and therefore exposed to human induced erosion processes.

The Mar Menor lagoon is one of the largest coastal lagoons (135 km2 surface) of the Mediterranean basin. It receives runoff waters coming from the nearby intensive agricultural area of Campo de Cartagena, which have led this lagoon to be declared as a sensitive area for eutrophication in June 2001 under European Directive 91/271/EEC and as a vulnerable zone for nitrates contamination in December 2002 under Directive 91/676/EEC. Moreover, the existence of mining activities (nowadays discontinued) in the nearby area of Sierra de Cartagena-La Union has caused the spread of metal polluted wastes into the Mar Menor lagoon and its salt marshes. As a consequence, huge coastal areas are buried by metal enriched wastes, and although most of them have been colonized by vegetation, others remain bare and exposed to erosive agents (e.g. wind, water). At the same time, the Mar Menor and its salt marshes have been included in the Ramsar Convention on Wetlands. Also, it is a Special Protected Area of Mediterranean Interest (SPAMI), a Specially Protected Area (SPA) under the EU Wild Birds Directive and a Site of Community Importance (SCI) to be integrated in the Nature 2000 Network (EU Habitats Directive). In addition, the Campo de Cartagena- Mar Menor zone hosts important economic activities related with agriculture, fisheries and tourism (Conesa and Jiménez-Cárceles, 2007). Hence, the habitat conservation and the uses of the territory must be compatible and overcome the environmental problems of the zone. This paper summarizes several studies carried out in the Mar Menor area from year 2000 till nowadays. The methodologies followed in these works were based on international scientific and technical protocols. The research included field and lab experiments. The first ones had the goal of answering questions such as what, where, when, by means of descriptive field survey studies (Álvarez-Rogel et al., 2000, 2001, 2006b, 2007a y c, Álvarez-Rogel et al., 2006a, 2007b; Jiménez-Cárceles, 2007; Jiménez-Cárceles et al., 2006; Jiménez-Cárceles and Álvarez-Rogel, 2008; Egea et al., 2011). Afterwards, the research had the goal of explaining how the processes occurred, by means of experimental set ups not included here (greenhouse experiments, columns, lab, etc.). This chapter deals with the field survey studies in order to describe the nutrient dynamics and eutrophication risks in the coastal areas of the Mar Menor lagoon

Los humedales se pueden definir como cualquier anomalía hídrica positiva en el paisaje, de origen natural o artificial, que no es ni un río ni un lago, y que se caracteriza por presentar comunidades biológicas o usos característicos que la diferencian del entorno (González- Bernáldez, 1988). Estos ecosistemas son de gran interés para la preservación de la biodiversidad, por encontrarse en ellos el hábitat de especies animales y vegetales en peligro de extinción. Pero además, los humedales son sistemas idóneos para combatir la contaminación difusa originada, por ejemplo, por vertidos de aguas residuales, excedentes agrícolas o sedimentos y aguas con elevados contenidos en metales tóxicos. Por este motivo se les ha llamado filtros verdes.

[SPA] El Mar Menor, localizado en el sureste de España, es una de las lagunas costeras más grandes de Europa y del Mediterráneo. A pesar de las diversas figuras de protección medioambiental que obstenta, esta laguna y sus humedales asociados se encuentran afectados por diversas actividades antrópicas, entre las que destacan la presencia de residuos mineros procedentes de la antigua zona minera de Cartagena-La Unión, transportados y depositados durante los periodos de lluvias torrenciales a través de las ramblas que drenan ese área. Como caso de estudio, el presente trabajo se centra en dos saladares, la Marina del Carmolí y Lo Poyo, y en la línea de costa del Mar Menor asociada a ambos parajes. [ENG] The present work focuses on two salt marshes, the Marina del Carmolí and Lo Poyo, and along the shoreline of the Mar Menor associated to both wetlands. Due to the activities that population develops in the area, which include harvesting of plants for feeding and adornment, sheepherding, capture of molluscs for eating, several recreational activities, and bathing, there may be some risks of toxicity and transfer of heavy metals and arsenic to the food chain. Thus, it was proposed a project with the following aims: (1) To carry out a first approximation to the risks of toxicity associated with the presence of heavy metals and arsenic in these environments, including their transfer to the food chain. (2) To study the biogeochemical processes associated with mobilization-immobilization of those toxic elements in the studied wetlands, under different flooding regimes either with or without rhizosphere. (3) To establish recommendations for use to preserve these ecosystems and reduce the risks associated with the presence of those contaminants. To achieve the first aim, the concentrations of heavy metals (cadmium, copper, manganese, lead, and zinc) and arsenic were determined in several rhizospheric and non-rhizospheric soil samples (total contents and the labile fraction extracted with 1 N hydrochloric acid) and in the most representative species of plants of both salt marshes, including those consumed by population and those used for sheepherding. Litter, roots, rhizomes, bulbs, green stems, ligneous stems, and leaves were separately analyzed. With the same objective, it was determined the accumulation of the same toxic elements in the sediments of the lagoon in sites adjacent to both salt marshes and in two species of marine molluscs collected that live in them and which are consumed by population: the carnivorous gastropod Hexaplex trunculus (commonly called 'seashell' or 'horn'), and a filter bivalve, the clam Tapes decussatus. Besides, it was determined the speciation of arsenic in H. trunculus because the different forms of this metalloid have very different toxicities. To achieve the second aim, it was performed a greenhouse experiment to study the influence of pH, flooding and rhizosphere on the mobilization of cited elements plus iron. For that, different pots were filled with mining wastes collected from two polluted areas: one acidic (from Lo Poyo salt marsh) and one basic (from the Marina del Carmolí salt marsh). For each mining waste, small specimens of Sarcocornia fruticosa and Phragmites australis were planted in the pots. Also, it was prepared pots without plant. Two different flooding regime were applied: (1) pots flooded three months and afterwards drying, and (2) pots flooded one month and another drying, alternately for six months. The water used to irrigate the pots was a mixture of water collected from two of the main surface watercourses of the zone. The Eh and pH were measured weekly with appropriate electrodes. Also the solution was extracted weekly from the pots using Rhizon type samplers. After acidifying the solution with two drops of concentrated sulphuric acid, dissolved organic carbon and dissolved As, Cd, Cu, Mn, Pb, Zn and Fe were measured. To achieve the third aim, the results and conclusions of the two previous points were integrated and combined. The results of field analyses indicated that the soils of the Marina del Carmolí and Lo Poyo salt marshes are strongly polluted by As, Cd, Mn, Pb, and Zn, but not for copper. Besides, the contents extracted with 1 N hydrochloric acid (a labile fraction) were high, which indicate that there is a risk of mobilization of those elements. Therefore, according to field and greenhouse data, it can be proposed some recommendations in order to minimize the risks due to metallic pollution. A possible strategy would be the continuous flooding of the polluted areas, together with the planting of the most appropriate species to perform a phytostabilization program. Based on the capacity to grow in the wettest soils and on their capability to accumulate toxic elements in roots, Arthrocnemum macrostachyum, Sarcocornia fruticosa, Juncus maritimus, Scirpus holoschoenus, and Phragmites australis, would be the most suitable species. The presence of vegetation also would prevent the erosion and the dragging of the mining wastes. Nevertheless, these practices should be accompanied with the addition of some kind of amendment to further immobilize the contaminants, as for example carbonates. After the addition of amendments it is necessary to follow a monitoring program in the areas in restoration in order to check that those actions are effective enough in short and long term. Universidad Politécnica de Cartagena

The Mar Menor lagoon (SE Spain) is one of the largest coastal lagoons of the Mediterranean basin (135 km2 surface). The lagoon and its associated wetlands are affected by eutrophic water of agricultural and urban origin, with high loads of nitrogen and phosphorus, and by metal mine wastes carried by the surface watercourses coming from the former mining area of Sierra de Cartagena-La Unión. The objectives of this work were: 1) To study the biogeochemical processes related to the dynamics of nitrogen and phosphorus in the soil-water-plant system of eutrophic wetlands polluted by metal mine wastes, in order to identify their possible role as sinks or sources of both nutrients, and 2) To assay the effect of liming, presence of plants, and hydric/flooding conditions on metals mobility in the soil-water-plant system of eutrophic wetlands polluted by metal mine wastes, in order to identify the advantages and drawbacks of these conventional remediation treatments. To achieve these objectives, three experimental studies were performed under greenhouse conditions. In the experiments, soils polluted by metal mine wastes from the Marina del Carmolí and the Lo Poyo salt marshes, and plant species typical of these environments (Sarcocornia fruticosa and Phragmites australis) were used. In addition, eutrophic water from local surface watercourses and eutrophic water synthetically prepared were employed. In the first experiment, loam soils from the Marina del Carmolí (pH~7.8) and sandy-loam soils from the Lo Poyo salt marsh (pH~6.2) were used. Three pot treatments were assayed: S. fruticosa, P. australis, and bare soil. The pots were flooded for 15 weeks with eutrophic water, and pH, Eh, and the concentrations of NO3-, PO43-, and water-soluble organic carbon in the soil solution were regularly monitored. Before and after the flooding period, a soil P-fractionation was performed. -In relation to N dynamics, the NO3- concentrations in the soil solution decreased between 70 and 90% by the second day of flooding, except in the unvegetated pots with the soil of pH~6.2. Denitrification was the main mechanism associated to the removal of NO3-. The role of vegetation in improving the rhizospheric environment was relevant in the soil of pH~6.2 because higher sand content, lower pH, and higher soluble metal concentrations might strongly hinder microbial activity. -In relation to P dynamics, the PO43- concentrations in the soil solution decreased between 80 and 90% after three hours of flooding, with and without vegetation. The Fe/Mn/Al oxides and the Ca/Mg compounds played an important role in soil P retention. In the pots with S. fruticosa, the reductive conditions induced P release from metal oxides and P retention to Ca/Mg compounds. In turn, P. australis may have favoured the release of P from carbonates, which was transferred to Fe/Mn/Al compounds. In the second experiment, soils with fine texture from the Marina del Carmolí (in this case of pH~6.4) and sandy soils from the Lo Poyo salt marsh (in this case of pH~3.1) were used. Each type of polluted soil was mixed with a lime amendment (dose of 20 g kg-1), assaying two treatments: non-limed and limed soil. Cuttings of S. fruticosa were planted in pots prepared with the soil treatments. The pots were irrigated for 10 months with eutrophic water and soluble metal concentrations (Al, Cd, Mn, Pb, and Zn) and plant survival, plant biomass, and plant metal content were determined. The lime amendment decreased the concentrations of soluble metals and favoured the growth of S. fruticosa, enhancing the capacity of the plant to phytostabilise metals in roots. In the third experiment, soils with fine texture from the Marina del Carmolí (in this case of pH~6.4) and sandy soils from the Lo Poyo salt marsh (in this case of pH~3.1) were used. Each type of polluted soil was mixed with a lime amendment (dose of 20 g kg-1). Simulated soil profiles (60 cm depth) were constructed and four treatments were assayed: without liming + without plant, without liming + with plant, with liming + without plant, and with liming + with plant. The plant species employed was S. fruticosa. Three horizons were differentiated in the soil profiles: A (never under water), C1 (alternating flooding-drying conditions), and C2 (always under water). The pH, Eh, and soluble metal concentrations (Cd, Cu, Fe, Mn, Pb, and Zn) were measured regularly at each depth for 18 weeks. At the end of the experiment a soil metal-fractionation was applied. The lime amendment favoured the growth of S. fruticosa, an increase in pH, and a drop in Eh. -In relation to Fe dynamics, liming decreased Fe solubility, mainly in the soil of pH~3.1, but also facilitated a drop in Eh, favouring the dissolution of amorphous Fe oxides and hence increasing the concentration of soluble Fe. The plant rhizosphere contributed to the decrease of Eh and actively re-distributed the dissolved Fe along the soil profiles. -In relation to Cd, Cu, Mn, Pb, and Zn dynamics in the soil of pH~6.4, the lime amendment was effective for immobilising Mn, Zn, and Cd, but not Cu and Pb. The growth of S. fruticosa counteracted the effect of liming, strongly increasing the concentrations of soluble metals and distributing them through the soil profiles. -In relation to Cd, Cu, Mn, Pb, and Zn dynamics in the soil of pH~3.1, liming was effective for immobilising Zn, Cu, and Pb, but not Mn and Cd. The amendment increased the contents of Zn, Mn, and Cd bound to potentially-mobilisable soil fractions at the expense of the most-environmentally-inert fractions. In conclusion, the choice of the most appropriate phytomanagement techniques for recovering eutrophic wetlands polluted by metal mine wastes depends on the particular characteristics of the soil-water-plant system, the hydric/flooding regime, and the type of pollutant (nitrogen, phosphorus, and metals)., Universidad Politécnica de Cartagena

[SPA] Los humedales naturales y artificiales son sistemas capaces de transformar y/o eliminar compuestos nocivos, depurando las aguas eutrofizadas y/o contaminadas que fluyen a través de los mismos. Su papel como filtros verdes está determinado, fundamentalmente, por los procesos biogeoquímicos asociados a los cambios en las condiciones de oxidación-reducción, tales como la desnitrificación, así como por la fijación de contaminantes a diversos componentes del suelo, su precipitación y co-precipitación con otros compuestos e inmovilización en la biomasa vegetal. La laguna del Mar Menor y sus humedales asociados (por ejemplo, la Marina del Carmolí), se encuentran afectados por vertidos de aguas eutrofizadas de origen agrícola y urbano, con altas concentraciones de N y P. El deterioro de la calidad de las aguas de la laguna se ha acentuado en los últimos años, debido principalmente al aumento del grado de eutrofización, conduciendo a una crisis medioambiental en 2016. El objetivo principal de la Tesis fue estudiar, en condiciones experimentales, los procesos biogeoquímicos, microbiológicos y fisiológicos en el sistema suelo-agua-planta de humedales del entorno del Mar Menor afectados por aguas eutrofizadas, bajo condiciones alternantes de inundación-secado, a fin de determinar en qué medida la presencia de plantas de Phragmites australis, la carga de nutrientes (C orgánico, N y P) y el periodo del año influyen en la capacidad de estos sistemas para depurar aguas eutrofizadas y su relación con la emisión de CO2 y N2O. Los objetivos específicos fueron: 1. Evaluar el papel de la carga de nutrientes del agua de inundación y la presencia de Phragmites australis en la variabilidad estacional de las propiedades físico-químicas y microbiológicas del suelo, así como de las emisiones de CO2, en humedales afectados por aguas eutrofizadas. 2. Evaluar la capacidad de eliminación de N-N2O del suelo, el humedales afectados por aguas eutrofizadas, y determinar si dichos procesos están condicionados por la carga de nutrientes, la presencia de Phragmites australis y el periodo del año. 3. Evaluar la capacidad de retención de P en humedales afectados por aguas eutrofizadas y determinar si dicha retención está condicionada por la carga de nutrientes, la presencia de Phragmites australis y el periodo del año, así como la contribución de las plantas y de diferentes componentes del suelo en la retención de P., [ENG] Wetlands have the capacity to transformand/or remove harmful compounds (e.g. nutrients), improving the quality of eutrophic and/or contaminated waters flowing through them. Their role as green filters mainly depend on the biogeochemical processes related to the changes in the oxidation reduction conditions, such as denitrification, as well as on the fixation of contaminants to various soil components, their precipitation or co –precipitation with other substances and their immobilization in plant biomass. The Mar Menor lagoon (SE Spain), with 135 km2 of surface area, is the largest coastal lagoon of the Mediterranean basin. The lagoon and its associated wetlands (e.g. Marina del Carmolí salt marsh) are affected by eutrophic waters of agricultural and urban origin, with high loads of nitrogen (N) and phosphorus (P). The wáter quality deterioration of the lagoon has increased in the last years, mainly due to its eutrophication, leading to an environmental crisis in 2016. The general objective of the PhD Thesis was to study, under experimental conditions, the biogeochemical, microbiological and physiological processes in the soil –water–plant system of the Mar Menor’s wetlands affected by eutrophic waters, under alternating flooding–drying conditions, in order to assess to what extent the presence of Phragmites australis ,the nutrient load (organic carbon, N and P) and the time of the year influence the capacity of these systems to depurate eutrophic waters and its relation to carbon dioxide (CO2) and nitrous oxide (N2O) emissions., Esta Tesis se ha realizado bajo la financiación del siguiente proyecto: Relaciones entre los ciclos biogeoquímicos y la función de los humedales como filtros verdes: efecto de la eutrofización, la especie vegetal y el periodo del año sobre el secuestro de carbono ”, cofinanciado por el Ministerio de Economía y Competitividad (CGL2010–20214)–Fondos FEDER, Escuela Internacional de Doctorado, Universidad Politécnica de Cartagena, Programa Doctorado en Técnicas Avanzadas en Investigación y Desarrollo Agrario y Alimentario