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Drought Variability and Land Degradation in Semiarid Regions: Assessment Using Remote Sensing Data and Drought Indices (1982–2011)
No full textWe analyzed potential land degradation processes in semiarid regions worldwide using long time series of remote sensing images and the Normalized Difference Vegetation Index (NDVI) for the period 1981 to 2011. The objectives of the study were to identify semiarid regions showing a marked decrease in potential vegetation activity, indicative of the occurrence of land degradation processes, and to assess the possible influence of the observed drought trends quantified using the Standardized Precipitation Evapotranspiration Index (SPEI). We found that the NDVI values recorded during the period of maximum vegetation activity (NDVImax) predominantly showed a positive evolution in the majority of the semiarid regions assessed, but NDVImax was highly correlated with drought variability, and the trends of drought events influenced trends in NDVImax at the global scale. The semiarid regions that showed most increase in NDVImax (the Sahel, northern Australia, South Africa) were characterized by a clear positive trend in the SPEI values, indicative of conditions of greater humidity and lesser drought conditions. While changes in drought severity may be an important driver of NDVI trends and land degradation processes in semiarid regions worldwide, drought did not apparently explain some of the observed changes in NDVImax. This reflects the complexity of vegetation activity processes in the world's semiarid regions, and the difficulty of defining a universal response to drought in these regions, where a number of factors (natural and anthropogenic) may also affect on land degradation
Las galerías drenantes en Alcalá de Henares
No full textLa mayor parte del agua dulce disponible se encuentra en el subsuelo y al igual que en otras regiones del planeta que han tenido influencia musulmana, en España perviven gran cantidad de infraestructuras hidráulicas, que históricamente sirvieron para el aprovechamiento de este recurso tan importante para la vida. La capacidad del agua como agente transformador del paisaje y del territorio es proverbial, valga el ejemplo de los oasis del desierto, que en muchos casos fueron creados mediante la utilización de una técnica milenaria de captación de agua subterránea llamada ¿qanat¿, originaria de la antigua Persia y que los romanos primero y los musulmanes después se encargaron de difundir. La geografía de la península Ibérica está repleta de magníficos ejemplos de estas infraestructuras que abastecían a pueblos y ciudades, como Madrid. Este patrimonio ha caído en muchos casos en el olvido. Otro ejemplo sobresaliente es el de Alcalá de Henares que dispone de una extensa red de estas minas, cuyo origen está ligado al de su esplendoroso pasado universitario. En este trabajo de recuperación para la memoria colectiva de estas infraestructuras y de estudio de su influencia en la historia, han sido especialmente determinantes, por un lado, la investigación y georreferenciación de la cartografía histórica y actual y por otro la representación gráfica de los resultados de la investigación
Tratamiento de aguas residuales procedentes de un edificio de oficinas mediante un filtro verde intensivo
No full textThe objective of the present work is to evaluate the treatment capacity of the unsaturated zone (UZ) to remove contaminants from a wastewater effluent using a vegetation filter. The wastewater effluent originates from an office building and it is characterized by a high organic carbon and nitrogen load. Prior to its application over the vegetation filter, the raw wastewater is primary treated with an Imhoff tank. The vegetation filter surface is 77 m2 and it has been designed with an intensive plantation density (10,000 plants/ha) to maximize the plants nutrients uptake. The system efficiency has been controlled with a Gee Passive Capillary Lysimeter installed at 90 cm depth that allows a periodical sampling of the infiltrating water through the UZ. Furthermore, the potential groundwater affection derived from the wastewater application was monitored in a downgradient piezometer.
The vegetation filter presents a high contaminant removal: up to 85% in terms of concentration in the cases of chemical oxygen demand (COD) and dissolved organic carbon (DOC), 90% for total phosphorus (PT) and 73% for total nitrogen (NT). When the efficiency is evaluated in terms of mass, the values are much higher, reaching 90% of removal for NT. No significant affection was observed in groundwater quality as a consequence of the leaching from the vegetation filter
Continuous cycling of an asymmetric capacitive deionization system: An evaluation of the electrode performance and stability
No full textCapacitive deionization (CDI) shows great promise as an energy efficient water treatment technology. However, much of the research has focused on brackish water desalination and/or NaCl removal while ignoring other ions that may pose challenges for CDI and should be addressed. In this work, we studied the effects of modifying operational parameters in a CDI system operating in a continuous adsorption/desorption cycle using CaSO4, as well as other electrolytes. Low-cost, high surface area carbons coated with two different metal oxides (SiO2 on the cathode and Al2O3 on the anode) were employed as electrodes in the CDI reactor. Two ion adsorption mechanisms, electrosorption in the electrochemical double layer (EDL) and specific adsorption on the oxide surfaces and carbon support, appeared to play a role in the ion removal process. During regeneration of the electrodes, poor CaSO4 desorption likely associated with specific adsorption on the metal oxide coatings, along with diffusional issues, led to salt accumulation on the electrodes. Electrode regeneration values above 95% were obtained when chloride-containing electrolytes were employed, indicating that SO42− interactions were the main cause of the poor desorption. The mode of regeneration also strongly influenced ion desorption kinetics and charge efficiencies during subsequent removal cycles. Long-term experiments revealed that oxidation of the anode affected the electrosorption of ions and induced acidification of the solution
Environmental risk of combined emerging pollutants in terrestrial environments: chlorophyll a fluorescence analysis
No full textThe risk assessment in terrestrial environments has been scarcely studied for mixtures of organic contaminants. To estimate toxicity due to these compounds, an ecotoxicological test may be done with the appropriate organism and biomarker. Photosynthesis is principally performed at photosystem II, and its efficiency is affected by any environmental stress. Consequently, the measure of this efficiency may be a good indicator of toxicity if different parameters are employed, e.g., the quantum efficiency of photosystem II and the photochemical quenching coefficient. We did a series of assays to determine the toxicity of two organic contaminants, ibuprofen and perfluorooctanoic acid, using a higher plant (Sorghum bicolor). The results showed more toxicity for the perfluorinated compound and greater sensibility for the quantum efficiency of photosystem II. Regarding the binary combination, three methods were applied to calculate EC50: combination index, concentration addition, and independent action. Synergistic behavior is the principal toxicological profile for this mix. Therefore, the combination index, which considers interactions among chemicals, gave the best estimation to determine risk indices. We conclude that the inhibition of photosynthesis efficiency can be a useful tool to determine the toxicity of the mixtures of organic pollutants and to estimate ecological risks in terrestrial environments
