Dynamics of nitrogen, phosphorus and metals in eutrophic wetlands affected by mine wastes. Effects of liming on plant growth and metals mobility

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 Cartagen

Variations in Plant Zonation and Cover as Indicators of long-term changes in soil conditions: a case study in a mediterranean coastal salt marsh

This study summarizes the changes (1991-2004) in plant distribution and cover in relation to soil factors in a salt marsh impacted by surplus of water from agricultural origin. An elevation of the groundwater level was observed, which led to a homogenization in the saline gradient. The changes were reflected in a shift in vegetation distribution which included the disappearance of most of the zonation observed in 1991

Metal mobility assessment in semiarid mine tailings amended with biochar and urban compost: results of a bioassay employing a pioneer plant species

[SPA] El fitomanejo permite reducir el riesgo ambiental de balsas mineras abandonadas. El objetivo del trabajo fue evaluar la movilidad de metales en balsas mineras enmendadas con biochar y/o compost urbano y la efectividad de las enmiendas reduciendo la toxicidad de la solución edáfica para una planta pionera (Zygophyllum fabago). Se llevó a cabo un experimento en mesocosmos (20 meses) con residuo minero con y sin enmienda. Los mesocosmos se mantuvieron a capacidad de campo con agua de la red y se drenaron en diferentes momentos. Se monitorizó la solución edáfica regularmente (pH, conductividad eléctrica, carbono orgánico soluble –COS--, nitrógeno total soluble –NTS- y metales -Mn, Zn-), al igual que el drenaje. Se realizó un bioensayo con semillas de Z. fabago con la solución edáfica de mitad del experimento (germinación de semillas, crecimiento de plántulas). Los tratamientos con compost urbano mostraron mayor concentración inicial de COS y metales en solución. Se observó un descenso temporal de la concentración de DOC y metales en la solución edáfica debido a su lixiviación en el drenaje. A pesar del mayor contenido de metales, el compost urbano favoreció la elongación de la raíz debido al mayor contenido de COS y NTS en solución. [ENG] Phytomanagement allows to reduce the environmental risks of abandoned mine tailings. The aim of this work was to assess metal mobility in mine tailings amended with biochar and/or urban compost and the effectiveness of these amendments for reducing the toxicity of soil solution to a pioneer plant species (Zygophyllum fabago). A mesocosm experiment was performed (20 months) with mine wastes with and without amendment. Mesocosms were maintained at field capacity with tap water and drained at different times. Soil solution was regularly monitored (pH, electrical conductivity, dissolved organic carbon –DOC-, dissolved total nitrogen –TDN- and metals -Mn, Zn-), as well as drainage. A bioassay with seeds of Z. fabago was performed with midterm soil solution (seed germination, seedling performance). Treatments containing urban compost showed higher initial DOC and metal concentrations in solution. A decrease of DOC and metal concentrations in soil solution with time occurred due to their lixiviation in the drainage water. In spite of the higher metal pool, urban compost favoured root length due to its greater content of DOC and TDN in soil solution.Financial support for this research was provided by the Ministerio de Economía y Competitividad of Spain and FEDER (Project CTM2014-54029-R) and Fundación Séneca de CARM (19248/PI/14). Obdulia Martínez holds a FPI contract from the Ministerio de Economía y Competitividad of Spain (BES-2015-075838). Dr. González-Alcaraz holds a Marie Skłodowska-Curie contract (H2020-MSCA-IF-2015, Project ID 704332)

Spontaneous vegetation colonizing abandoned metal(loid) mine tailings consistently modulates climatic, chemical and biological soil conditions throughout seasons

This study aimed to evaluate whether the improvement in soil conditions induced by the vegetation spontaneously colonizing abandoned metal(loid) mine tailings from semiarid areas is consistent throughout seasons and to identify if the temporal variability of that conditions is of similar magnitude of that of the surrounding forests. Soil climatic (temperature and moisture), chemical (pH, electrical conductivity and water-soluble salts and metal(loid)s) and biological (water-soluble organic carbon and ammonium, microbial biomass carbon, dehydrogenase and β-glucosidase activity, organic matter decomposition and feeding activity of soil dwelling organisms) parameters were seasonally evaluated for one year in bare soils and different vegetated patches within metalliferous mine tailings and surrounding forests in southeast Spain. The results indicated that the improvement in soil conditions (as shown by softening of climatic conditions and lower scores for salinity and water-soluble metals and higher for biological parameters) induced by vegetation colonization was consistent throughout seasons. This amelioration was more evident in the more complex vegetation patches (trees with herbs and shrubs under the canopy), compared to bare soils and simpler soil-plant systems (only trees), and closer to forest soils outside the tailings. Bare soils and, to a lesser extent, vegetation patches solely composed by trees, showed stronger seasonal variability in temperature, moisture content, salinity, and water-soluble metals. In contrast, changes in biological and biological-related parameters were more pronounced in the more complex vegetation patches within mine tailings and surrounding forests due to its greater biological activity. In summary, the results demonstrated that vegetation patches formed by spontaneous colonization act as microsites that modulate seasonal variability in soil conditions and stimulate biological activity. This suggests that tailings vegetation patches might have higher resilience against climate change effects than bare soils. Therefore, they should be preserved as valuable spots in the phytomanagement of metal(loid)s mine tailings from semiarid areas.The present study was supported by the project RESCLICONT (CGL2016-80981-R) funded by MCIN/AEI/10.13039/501100011033/ and FEDER A way to make Europe. A. Peñalver-Alcalá was hired by the project RESCLICONT. 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 Irene Sánchez during field and laboratory work. Francisco J. Jiménez-Cárceles, from Biocyma environmental consulting, helped us in vegetation field work. We thank to the technicians of the SAIT-UPCT for their laboratory and analytical assessments

Long-term artificial seawater irrigation as a sustainable environmental management strategy for abandoned solar salt works: The case study of Agua Amarga salt marsh (SE Spain)

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

Functional and structural soil regeneration in abandoned mine tailings from semiarid Mediterranean areas: relationships with spontaneous plant colonization

[SPA] Los ecosistemas terrestres degradados por residuos mineros, cuyas características funcionales y estructurales están deterioradas, pueden presentar condiciones estresantes para los organismos vivos, además de suponer un riesgo de transferencia de compuestos potencialmente tóxicos al medio. El objetivo de este trabajo fue evaluar el desarrollo edáfico, estructural y funcional, del suelo asociado a distintas etapas de colonización vegetal espontánea, relacionados con la regeneración del ecosistema, en ambientes Mediterráneos afectados por residuos mineros. Se evaluaron diversos parámetros estructurales (estructura; pH; salinidad; carbono orgánico total; nitrógeno total; metales) y funcionales (carbono de la biomasa microbiana; la actividad β-glucosidasa; el estudio de grupos funcionales de microorganismos) del suelo de cinco ambientes degradados con diferente grado de colonización vegetal, además de en un bosque control sin contaminación. Se observó que existen diferencias estructurales y funcionales entre ambientes, con propiedades del suelo y respuestas funcionales de los ecosistemas más próximas a las del bosque control en los ambientes con mayor colonización vegetal. [ENG] Terrestrial ecosystems degraded by mine waste with functional and structural characteristics deteriorated, can present stressful conditions to organisms, also to mean a transfer risk of potentially toxic compounds to environment. The aim of this study was to assess the soil development, structural and functional, associated to different spontaneous plant colonization stages related with ecosystem regeneration, in Mediterranean environments affected by mine waste. Structural (structure; pH; salinity; total organic carbon; total nitrogen; metals) and functional (microbial biomass carbon; β-glucosidase activity; functional groups of microorganisms study) soil parameters were evaluated in five degraded environments with different plant colonization stage, as well as, a control forest without pollution. Structural and functional differences between environments were observed, with soil properties and functional response of ecosystems closer to control forest in the environments with higher plant colonization.Trabajo financiado por el Ministerio de Industria, Economía y Competitividad (CGL2016-80981-R) y por fondos FEDER y por Campus Mare Nostrum de Excelencia Internacional a través de su Ayuda para la realización de estancias externas de jóvenes investigadores asociados a redes y nodos CMN durante el curso académico 2018/2019

Carbon and nitrogen mineralization in metal mine tailings technically recovered vs. abandoned spontaneously colonized by vegetation as indicator to assess soil functionality

[SPA] Los residuos mineros metalíferos se encuentran entre los ambientes más inhóspitos para la biota (altos niveles de metales/metaloides, pH extremos, alta salinidad, escasa materia orgánica y nutrientes). A menudo estos residuos se depositan en pilas al aire libre (depósitos de residuos mineros), que clásicamente son restaurados mediante técnicas de cubrición con suelo limpio y posterior plantación. Una alternativa es favorecer el crecimiento de especies vegetales sobre los residuos, contribuyendo a crear sistemas suelo-planta funcionales, como han demostrado estudios previos. El objetivo del trabajo fue evaluar cómo los suelos de depósitos técnicamente restaurados y los abandonados colonizados espontáneamente por la vegetación difieren en su capacidad para mineralizar carbono y nitrógeno. Los resultados muestran que los suelos de ambos depósitos son funcionales, y tienen un potencial similar para mineralizar nitrógeno. Sin embargo, los suelos del depósito restaurado mostraron mayor capacidad de mineralizar carbono. [ENG] Metal mine wastes are among the most hostile environments for biota (high metal/metalloid levels, extreme pH, high salinity, low organic matter and nutrients). These wastes are often stored in open-air piles (mine tailings) that are classically restored with techniques of topsoil capping and then afforestation. An alternative is to promote the growth of native plant species directly in mine wastes, which help to create functional soil- plant systems, as previous studies showed. This work aimed to evaluate how technically reclaimed and abandoned spontaneously colonized metal(loid) mine tailings’ soils differ in their ability to mineralize carbon and nitrogen. The results show that the soils of both mine tailings are functional and have a similar potential to mineralize nitrogen. However, the soils of the restored reservoir showed a greater capacity to mineralize carbon.Trabajo financiado por MCIN/AEI/10.13039/501100011033 (PID2020-118941RA-I00) y la UPCT (Contrato Predoctoral FPI). M.N. González-Alcaraz es investigadora Ramón y Cajal del Ministerio de Ciencia e Innovación de España (RYC2020-029322-I)

Functional regeneration of soils affected by mine wastes in Mediterranean environments and their resilience against climate change scenarios

[SPA] Los suelos afectados por residuos mineros pueden presentar condiciones estresantes para los organismos vivos, además de suponer un riesgo de transferencia de compuestos potencialmente tóxicos al medio. Esto podría verse agravado en un futuro, ya que tales suelos, cuyas características funcionales y estructurales están deterioradas, tendrán menor capacidad de adaptación (resiliencia) frente al cambio climático. El objetivo de la tesis doctoral es conocer aspectos funcionales y estructurales del suelo relacionados con la regeneración del ecosistema, en ambientes Mediterráneos afectados por residuos mineros, y valorar su resiliencia frente a escenarios de cambio climático. Para ello se estudiarán ambientes con distinto grado de colonización vegetal. Además, se pretende evaluar si la adición de enmiendas orgánicas puede contribuir a mejorar la funcionalidad de los suelos y su respuesta frente a dichos escenarios. Los resultados iniciales indican que pueden existir diferencias funcionales y estructurales entre los distintos ambientes seleccionados, relacionadas con diferentes etapas de colonización vegetal. La adición de enmiendas orgánicas a estos suelos puede ser una práctica de manejo adecuada para mejorar sus propiedades. [ENG] Soils affected by mine wastes might show stressful conditions for biota, as well as to pose a risk of transfer of potentially toxic compounds to the environment. This may worsen in the upcoming decades since these soils, whose functional and structural characteristics are deteriorated, will have less adaptation capability (resilience) to climate change. The objective of the thesis is to know functional and structural aspects of the soil related to ecosystem regeneration, in Mediterranean environments affected by mine wastes, and to evaluate its resilience against climate change scenarios. Moreover, the aim is also to evaluate if organic amendments addition might improve soil functionality and its response to changing climate conditions. To achieve this, environments with different degree of vegetal colonization will be studied. The initial results show that functional and structural differences might exist among the different environments selected, in relation with the distinct stage of vegetal colonization. The addition of organic amendments to these soils could be an adequate management practice to improve their properties.Proyecto financiado por el Ministerio de Industria, Economía y Competitividad (CGL2016-80981-R) y por fondos FEDER

Effect and evolution of organic amendments application on the functionality of metallic mine tailings soils in environments under Mediterranean climate

[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)

Ciclos biogeoquímicos en humedales con diferente grado de eutrofización y su relación con factores de cambio climático: resultados experimentales en mesocosmos

La presente propuesta de Tesis se centra en el estudio de procesos microbiológicos y biogeoquímicos ligados a ciclos del carbono y nutrientes en el sistema planta‐sueloagua de humedales afectados por aguas con diferente grado de eutrofización, a fin de determinar en qué medida la presencia o no de planta, la carga de nutrientes y los periodos de inundación‐desecación influyen en la capacidad de estos sistemas para secuestrar carbono y actuar, al mismo tiempo, como filtros verdes y si esta función afecta a la producción de gases de efecto invernadero (N2O, CO2 y CH4). El experimento se realizará en mesocosmos experimentales sometidos a periodos de inundacióndesecación con dos aguas de diferente composición, una con alta carga de nutrientes y otra con baja carga. Se harán tres repeticiones por tratamiento: sin planta+baja carga de nutrientes; sin planta+alta carga de nutrientes; con planta+baja carga de nutrientes y con planta+alta carga de nutrientes. La utilizada elegida será Phragmites australis. Se medirá regularmente Eh, pH y temperatura del suelo y paralelamente se extraerá la solución edáfica para el análisis de N, P, C y metales. Se tomaran muestras de suelo para el análisis químico y microbiológico. Se cogerán muestras de los gases emitidos desde la superficie para la determinación de las concentraciones de N2O y CH4 y se medirá “in situ” el CO2 desprendido. Además, se cuantificaran y analizarán los drenajes, recogidos tras cada período de inundación, y también se estudiará la descomposición de hojarasca mediante bolsitas de hojarasca.Proyecto financiado por el Ministerio de Ciencia e Innovación. Referencia: CGL2010‐2021