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Papers by Maria Polo

Methods, Models, Simulations And Approaches Towards A General Theory Of Change, 2012

Methods, Models, Simulations And Approaches Towards A General Theory Of Change, 2012

Ecological Indicators, 2014

ABSTRACT Abstract This paper investigates the use of the vegetative state of natural covers as an... more ABSTRACT Abstract This paper investigates the use of the vegetative state of natural covers as an indicator of soil moisture conditions at the end of the dry season in order to evaluate the cumulative effect of the hydrological regime. To achieve this, the three major vegetation covers in a mountainous semiarid environment in southern Spain were selected. Temporal and spatial trends of NDVI from Landsat-TM images were computed and related to the different hydrological patterns of variables in the study site, which were obtained with the hydrological WiMMed model. The heterogeneity in the hydrological behavior during the study period (914.5 mm of annual rainfall in the wettest year (2009–2010) and 284.4 mm in the driest year (2004–2005)) was reflected in the annual differences in NDVI values with steady mean NDVI values in coniferous vegetation (0.5–0.6) and more variable values in scrub cover. Both Correlation Analysis and Principal Component Analysis showed correlations among the different states of the vegetation cover, the variables involved in the soil water balance and those related to the snow dynamics of the antecedent year. Exponential fits were obtained between the mean annual soil water content and NDVI values with Pearson r2 coefficients of over 0.7 in scrub cover. In certain years, the best fits were also found in scrub cover with r2 values of up to 0.9. These results demonstrate the relationship between soil water content, the vigor of the natural vegetation and the hydrological characteristics of the antecedent year. The expressions obtained may serve to adjust the soil water content at the beginning of a hydrological year and to use the scrub cover as an indicator of the soil water balance in the area for a given year.

Remote Sensing for Agriculture, Ecosystems, and Hydrology XIV, 2012

ABSTRACT In Mediterranean regions, where the water shortage is a serious and recurrent problem, i... more ABSTRACT In Mediterranean regions, where the water shortage is a serious and recurrent problem, it is essential to know the behaviour and evolution of the snow. Satellite remote sensing is widely used to find out the evolution of the snow cover extension at medium-large scales. But these techniques pose some constraints if snow is heterogeneously distributed, as they do not correctly represent the physical processes that occur on a smaller scale than the satellite image. In such cases, terrestrial photographs, whose resolution can be more easily adapted to the required resolution for these study cases, are an economic and also efficient alternative. This work presents a methodology for the georeferencing and automatic detection of snow in terrestrial photography, as an alternative to the use of satellite images for the study of the snow cover evolution in small areas. This methodology has been evaluated during the snowmelt period in the spring of 2009 at a study site in Sierra Nevada Natural Park (Southern Spain). The resulting snow maps have been compared with the results available for that period obtained from the analyses of four Landsat images. The results show that the use of Landsat generally overestimated the extension of the snow cover in the study area.

Remote Sensing for Agriculture, Ecosystems, and Hydrology XV, 2013

ABSTRACT The albedo of snow affects the shortwave radiative flux at the land-atmosphere interface... more ABSTRACT The albedo of snow affects the shortwave radiative flux at the land-atmosphere interface, so that it therefore plays an important role in the snow mass and energy balance. In semiarid areas, their particular climate conditions enhance the spatiotemporal variability of the snow albedo during the snow cover periods, increasing its difficulty in being measured and monitored. Satellite remote sensing is a powerful tool for measuring snow albedo evolution. Ten years of Landsat-5 and Landsat-7 Thematic Mapper images were analysed to determine a trend in the albedo evolution throughout the year in a Mediterranean site, Sierra Nevada Mountain (Southern Spain). A pattern in snow albedo from all the snow pixel in each Landsat scene was obtained. It ranges from 0.8 in new snow to 0.4 in old dirty snow, with a decreasing rate of 0.003 albedo per day. This trend was validated with 5 specific location, where the snow is more persistent while the pixel remains well-illuminated.

Ecological Indicators, 2014

ABSTRACT Abstract This paper investigates the use of the vegetative state of natural covers as an... more ABSTRACT Abstract This paper investigates the use of the vegetative state of natural covers as an indicator of soil moisture conditions at the end of the dry season in order to evaluate the cumulative effect of the hydrological regime. To achieve this, the three major vegetation covers in a mountainous semiarid environment in southern Spain were selected. Temporal and spatial trends of NDVI from Landsat-TM images were computed and related to the different hydrological patterns of variables in the study site, which were obtained with the hydrological WiMMed model. The heterogeneity in the hydrological behavior during the study period (914.5 mm of annual rainfall in the wettest year (2009–2010) and 284.4 mm in the driest year (2004–2005)) was reflected in the annual differences in NDVI values with steady mean NDVI values in coniferous vegetation (0.5–0.6) and more variable values in scrub cover. Both Correlation Analysis and Principal Component Analysis showed correlations among the different states of the vegetation cover, the variables involved in the soil water balance and those related to the snow dynamics of the antecedent year. Exponential fits were obtained between the mean annual soil water content and NDVI values with Pearson r2 coefficients of over 0.7 in scrub cover. In certain years, the best fits were also found in scrub cover with r2 values of up to 0.9. These results demonstrate the relationship between soil water content, the vigor of the natural vegetation and the hydrological characteristics of the antecedent year. The expressions obtained may serve to adjust the soil water content at the beginning of a hydrological year and to use the scrub cover as an indicator of the soil water balance in the area for a given year.

Remote Sensing for Agriculture, Ecosystems, and Hydrology XIV, 2012

ABSTRACT In Mediterranean regions, where the water shortage is a serious and recurrent problem, i... more ABSTRACT In Mediterranean regions, where the water shortage is a serious and recurrent problem, it is essential to know the behaviour and evolution of the snow. Satellite remote sensing is widely used to find out the evolution of the snow cover extension at medium-large scales. But these techniques pose some constraints if snow is heterogeneously distributed, as they do not correctly represent the physical processes that occur on a smaller scale than the satellite image. In such cases, terrestrial photographs, whose resolution can be more easily adapted to the required resolution for these study cases, are an economic and also efficient alternative. This work presents a methodology for the georeferencing and automatic detection of snow in terrestrial photography, as an alternative to the use of satellite images for the study of the snow cover evolution in small areas. This methodology has been evaluated during the snowmelt period in the spring of 2009 at a study site in Sierra Nevada Natural Park (Southern Spain). The resulting snow maps have been compared with the results available for that period obtained from the analyses of four Landsat images. The results show that the use of Landsat generally overestimated the extension of the snow cover in the study area.

Remote Sensing for Agriculture, Ecosystems, and Hydrology XV, 2013

ABSTRACT The albedo of snow affects the shortwave radiative flux at the land-atmosphere interface... more ABSTRACT The albedo of snow affects the shortwave radiative flux at the land-atmosphere interface, so that it therefore plays an important role in the snow mass and energy balance. In semiarid areas, their particular climate conditions enhance the spatiotemporal variability of the snow albedo during the snow cover periods, increasing its difficulty in being measured and monitored. Satellite remote sensing is a powerful tool for measuring snow albedo evolution. Ten years of Landsat-5 and Landsat-7 Thematic Mapper images were analysed to determine a trend in the albedo evolution throughout the year in a Mediterranean site, Sierra Nevada Mountain (Southern Spain). A pattern in snow albedo from all the snow pixel in each Landsat scene was obtained. It ranges from 0.8 in new snow to 0.4 in old dirty snow, with a decreasing rate of 0.003 albedo per day. This trend was validated with 5 specific location, where the snow is more persistent while the pixel remains well-illuminated.

Journal of chromatography. A, Jan 30, 2003

Headspace solid-phase microextraction, followed by GC-MS analysis is presented as a suitable tech... more Headspace solid-phase microextraction, followed by GC-MS analysis is presented as a suitable technique for the determination of musk compounds in sewage treatment plant sludge. Five polycyclic musks (celestolide, phantolide, traseolide, galaxolide and tonalide) and four nitro musks (musk xylene, musk moskene, musk tibetene and musk ketone) were considered in the optimisation of the analytical method. The influence of extraction temperature, fibre coating, agitation, pH and salting out on the efficiency of the extraction along with the extraction kinetics were studied. An extraction temperature of 100 degrees C and sampling the headspace over the stirred sludge sample using polydimethylsiloxane -divinylbenzene as fibre coating lead to effective extraction. The method proposed is very simple and yields high sensitivity, good linearity and repeatability for all the analytes with limits of detection at the sub-ng/g level. The total analysis time, including extraction and GC analysis, was only 40 min, and no manipulation of the sample was required.

Journal of chromatography. A, Jan 18, 2006

A solid-phase microextraction (SPME) method has been developed for the determination of pentachlo... more A solid-phase microextraction (SPME) method has been developed for the determination of pentachlorophenol (PCP) in paper and board samples. The analytical procedure involves direct extraction of PCP from paper and board samples and determination by gas chromatography with electron capture detection (GC-ECD). Two kinds of commercially available fibres; 100 m polydimethylsiloxane (PDMS), apolar, and 85 m polyacrylate (PA), quite polar, were evaluated to determine the extraction efficiency of pentachlorophenol. Parameters affecting the extraction process, such as temperature and time, were studied. Moreover, time of desorption and the effect of addition of salt were also investigated. The optimized procedure was applied to the analysis of pentachlorophenol (PCP) in five samples of virgin and recycled paper and board. The PCP content was determined by GC-ECD. To evaluate the effectiveness of the proposed method, it was compared with conventional extraction method with liquid-liquid extraction and derivatization. Detection limit of 0.015 g/g for PCP in paper was achieved with a RSD of 14%.

Analytical and bioanalytical chemistry, 2007

A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron ca... more A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron capture detection for determining trace levels of nitro musk fragrances in residual waters was optimized. Four nitro musks, musk xylene, musk moskene, musk tibetene and musk ketone, were selected for the optimization of the method. Factors affecting the extraction process were studied using a multivariate approach. Two extraction modes (direct SPME and headspace SPME) were tried at different extraction temperatures using two fiber coatings [Carboxen-polydimethylsiloxane (CAR/PDMS) and polydimethylsiloxane-divinylbenzene (PDMS/DVB)] selected among five commercial tested fibers. Sample agitation and the salting-out effect were also factors studied. The main effects and interactions between the factors were studied for all the target compounds. An extraction temperature of 100°C and sampling the headspace over the sample, using either CAR/PDMS or PDMS/DVB as fiber coatings, were found to be the experimental conditions that led to a more effective extraction. High sensitivity, with detection limits in the low nanogram per liter range, and good linearity and repeatability were achieved for all nitro musks. Since the method proposed performed well for real samples, it was applied to different water samples, including wastewater and sewage, in which some of the target compounds (musk xylene and musk ketone) were detected and quantified.

Journal of Chromatography A - J CHROMATOGR A, 2005

A solid-phase microextraction method (SPME) coupled to gas chromatography–mass spectrometry (GC–M... more A solid-phase microextraction method (SPME) coupled to gas chromatography–mass spectrometry (GC–MS) has been developed for the determination of the six phthalate esters included in the US Environmental Protection Agency (EPA) Priority Pollutants list in water samples. These compounds are dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), butylbenzyl phthalate (BBP), di-2-ethylhexyl phthalate (DEHP) and di-n-octyl phthalate (DOP). Detailed discussion of the different parameters, which could affect the extraction process, is presented. Main factors have been studied and optimized by means of a multifactor categorical design. Different commercial fibers, polydimethylsiloxane (PDMS), polydimethylsiloxane–divinylbenzene (PDMS–DVB), polyacrylate (PA), Carboxen–polydimethylsiloxane (CAR–PDMS) and Carbowax–divinylbenzene (CW–DVB), have been investigated, as well as the extraction mode, exposing the fiber directly into the sample (DSPME) or into the headspace over the sample (HS-SPME), and different extraction temperatures. The use of this experimental design allowed for the evaluation of interactions between factors. Extraction kinetics has also been studied. The optimized microextraction method showed linear response and good precision for all target analytes. Detection limits were estimated considering the contamination problems associated to phthalate analysis. They were in the low pg mL−1, excluding DEHP (100 pg mL−1). The applicability of the developed SPME method was demonstrated for several real water samples including mineral, river, industrial port and sewage water samples. All the target analytes were found in real samples. Levels of DEP and DEHP were over 1 ng mL−1 in some of the samples.

Journal of the Science of Food and Agriculture, 1992

Abstract: Several multivariate statistical methods (principal component, cluster, stepwise discri... more Abstract: Several multivariate statistical methods (principal component, cluster, stepwise discriminant and multiple linear regression analysis) were applied to analytical data obtained by conventional methods and to analytical data for free amino acids, in an attempt to distinguish between ...

Journal of Environment Quality, 2006

The residual pollution after the Aznalcóllar (southwestern Spain) pyrite mine spill is still a th... more The residual pollution after the Aznalcóllar (southwestern Spain) pyrite mine spill is still a threat due to the continuing oxidation of sulfuric minerals. The objective of this paper was to analyze the combined effect of pyrite oxidation, sugar beet foam applications, and meteorological conditions on the spatiotemporal evolution of the pH and EDTA-extractable Zn concentration, using non co-located data from 11 sampling dates between June 1999 and March 2002. Median pH values ranged from 4.4 at the beginning of the monitoring period to 7.6 at the end, although values near 2.5 were observed throughout the entire period, despite of two sugar beet foam (SBF) applications. Zinc distributions were positively skewed and median concentrations ranged from 17 to 94 mg kg(-1). The inverse relationship between pH and Zn became weaker toward the end of the monitoring period as a consequence of the precipitation and posterior dissolution of newly formed minerals from the reaction products of the pyrite oxidation. Normal score maps showed that after the SBF applications only 0.5% of the monitored area was below the pH = 4 threshold, while on other dates up to one-third of the area remained below this value. The better performance of the second SBF application could be explained in terms of pyrite oxidation pathways and environmental conditions. From this analysis, with data obtained under uncontrolled field conditions, it is concluded that SBF should be applied before or during the wet and cold season to alleviate acidification, caused by the oxidation of pyrite or other sulfuric minerals.

Journal of Environment Quality, 2006

Monitoring of soil chemical properties for pollution assessment generally requires destructive so... more Monitoring of soil chemical properties for pollution assessment generally requires destructive soil sampling and results in spatiotemporal datasets where data from different sampling dates are non co-located. The objective of this study was to assess the spatial distribution of residual pyrite sludge at a reclaimed site, using temporally non co-located data on pH; soil oxidizable fraction (SOF); and EDTA-extractable Fe, Zn, and Cu from six different sampling dates over a period of 2 yr. During this period spatially averaged pH and Zn concentrations ranged, respectively, from 4.4 to 6.6 and from 60 to 140 mg kg(-1), with minimum pH values of below 2.7. The data were merged into a single dataset for each chemical property after applying a normal score (ns) transform. Normal score pH was significantly negatively correlated with the ns metal concentrations. A principal component analysis (PCA) showed that normal score pH, Zn, and Fe were associated with the residual contamination, while ns Cu, SOF, and elevation were related with historic contamination. The spatial dependence between the properties was found to be scale-dependent. The best ns estimates were produced by ordinary kriging with an anisotopic variogram model, for the properties related with Principal Component (PC) I, while those associated with PC II were best estimated using simple kriging with varying local means. A classified ns pH map showed that 33% of the study area reached at least once values of below 4 during the 2-yr period. This part of the area should be excluded to ensure successful revegetation.

Journal of Chromatography A, 2006

A depletion solid-phase microextraction (SPME) method based on multiple SPME extraction was appli... more A depletion solid-phase microextraction (SPME) method based on multiple SPME extraction was applied to estimate fibre coating-water distribution constants (Kfs) of brominated flame retardants. Several polybrominated diphenyl ethers (PBDEs) including compounds present in the commercial mixture "Pentamix", and two polybrominated biphenyls (PBBs) were considered as target analytes. One hundred-micrometer poly(dimethylsiloxane) (PDMS) coating fibre was selected to estimate partition coefficients. SPME kinetics studies at 25 and 100 degrees C were performed. Kfs values obtained at both temperatures for brominated flame retardants were compared with the corresponding octanol-water partition coefficients (Kow) values found in literature. A linear log-log relationship between Kow with Kfs was found. To the best of our knowledge, this is the first study where brominated flame retardants Kfs values are estimated.

Journal of Agricultural and Food Chemistry, 2004

The anthocyanin pigments in rosé (Vitis vinifera cv. Garnacha) and blanc de noir (V. vinifera cv.... more The anthocyanin pigments in rosé (Vitis vinifera cv. Garnacha) and blanc de noir (V. vinifera cv. Monastrell) base and sparkling wines were studied by LC-DAD/ESI-MS. Anthocyanins of grape origin and pyranoanthocyanins resulting from C-4/C-5 cycloaddition of the former ones with pyruvic acid, acetaldehyde, 4-vinylphenol, 4-vinylguaiacol, and 4-vinylcatechol were identified in the different wines. Rosé wines presented a higher total pigment content than blanc de noir wines. Pyranoanthocyanins represented 68.9-76.0% of total pigment content in rosé wines and 49.4-60.7% in blanc de noir wines. Malvidin 3-glucoside-pyruvate was the most abundant pigment in both rosé and blanc de noir base wines. Important qualitative and quantitative changes were observed in terms of the anthocyanin and pyranoanthocyanin pigments after the second (bottle) fermentation and 9 months of aging on yeast lees, but not after a further time (3-9 additional months) of aging on lees. Evaluation of the wine color characteristics was consistent with a greater color stability for the rosé sparkling wines that could be associated with the high content, structural diversity, and spectroscopic features of the pyranoanthocyanins present in these wines.

Clinical Neurophysiology, 2003

Objective: Increased distractibility is a common impairment in alcoholism, but objective evidence... more Objective: Increased distractibility is a common impairment in alcoholism, but objective evidence has remained elusive. Here, a task designed to investigate with event-related brain potentials (ERPs) the neural mechanism underlying distraction was used to show abnormal involuntary orienting of attention in chronic alcoholism.

Analytical and Bioanalytical Chemistry, 2007

A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron ca... more A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron capture detection for determining trace levels of nitro musk fragrances in residual waters was optimized. Four nitro musks, musk xylene, musk moskene, musk tibetene and musk ketone, were selected for the optimization of the method. Factors affecting the extraction process were studied using a multivariate approach. Two extraction modes (direct SPME and headspace SPME) were tried at different extraction temperatures using two fiber coatings [Carboxen-polydimethylsiloxane (CAR/PDMS) and polydimethylsiloxane-divinylbenzene (PDMS/DVB)] selected among five commercial tested fibers. Sample agitation and the salting-out effect were also factors studied. The main effects and interactions between the factors were studied for all the target compounds. An extraction temperature of 100°C and sampling the headspace over the sample, using either CAR/PDMS or PDMS/DVB as fiber coatings, were found to be the experimental conditions that led to a more effective extraction. High sensitivity, with detection limits in the low nanogram per liter range, and good linearity and repeatability were achieved for all nitro musks. Since the method proposed performed well for real samples, it was applied to different water samples, including wastewater and sewage, in which some of the target compounds (musk xylene and musk ketone) were detected and quantified.

Methods, Models, Simulations And Approaches Towards A General Theory Of Change, 2012

Methods, Models, Simulations And Approaches Towards A General Theory Of Change, 2012

Ecological Indicators, 2014

ABSTRACT Abstract This paper investigates the use of the vegetative state of natural covers as an... more ABSTRACT Abstract This paper investigates the use of the vegetative state of natural covers as an indicator of soil moisture conditions at the end of the dry season in order to evaluate the cumulative effect of the hydrological regime. To achieve this, the three major vegetation covers in a mountainous semiarid environment in southern Spain were selected. Temporal and spatial trends of NDVI from Landsat-TM images were computed and related to the different hydrological patterns of variables in the study site, which were obtained with the hydrological WiMMed model. The heterogeneity in the hydrological behavior during the study period (914.5 mm of annual rainfall in the wettest year (2009–2010) and 284.4 mm in the driest year (2004–2005)) was reflected in the annual differences in NDVI values with steady mean NDVI values in coniferous vegetation (0.5–0.6) and more variable values in scrub cover. Both Correlation Analysis and Principal Component Analysis showed correlations among the different states of the vegetation cover, the variables involved in the soil water balance and those related to the snow dynamics of the antecedent year. Exponential fits were obtained between the mean annual soil water content and NDVI values with Pearson r2 coefficients of over 0.7 in scrub cover. In certain years, the best fits were also found in scrub cover with r2 values of up to 0.9. These results demonstrate the relationship between soil water content, the vigor of the natural vegetation and the hydrological characteristics of the antecedent year. The expressions obtained may serve to adjust the soil water content at the beginning of a hydrological year and to use the scrub cover as an indicator of the soil water balance in the area for a given year.

Remote Sensing for Agriculture, Ecosystems, and Hydrology XIV, 2012

ABSTRACT In Mediterranean regions, where the water shortage is a serious and recurrent problem, i... more ABSTRACT In Mediterranean regions, where the water shortage is a serious and recurrent problem, it is essential to know the behaviour and evolution of the snow. Satellite remote sensing is widely used to find out the evolution of the snow cover extension at medium-large scales. But these techniques pose some constraints if snow is heterogeneously distributed, as they do not correctly represent the physical processes that occur on a smaller scale than the satellite image. In such cases, terrestrial photographs, whose resolution can be more easily adapted to the required resolution for these study cases, are an economic and also efficient alternative. This work presents a methodology for the georeferencing and automatic detection of snow in terrestrial photography, as an alternative to the use of satellite images for the study of the snow cover evolution in small areas. This methodology has been evaluated during the snowmelt period in the spring of 2009 at a study site in Sierra Nevada Natural Park (Southern Spain). The resulting snow maps have been compared with the results available for that period obtained from the analyses of four Landsat images. The results show that the use of Landsat generally overestimated the extension of the snow cover in the study area.

Remote Sensing for Agriculture, Ecosystems, and Hydrology XV, 2013

ABSTRACT The albedo of snow affects the shortwave radiative flux at the land-atmosphere interface... more ABSTRACT The albedo of snow affects the shortwave radiative flux at the land-atmosphere interface, so that it therefore plays an important role in the snow mass and energy balance. In semiarid areas, their particular climate conditions enhance the spatiotemporal variability of the snow albedo during the snow cover periods, increasing its difficulty in being measured and monitored. Satellite remote sensing is a powerful tool for measuring snow albedo evolution. Ten years of Landsat-5 and Landsat-7 Thematic Mapper images were analysed to determine a trend in the albedo evolution throughout the year in a Mediterranean site, Sierra Nevada Mountain (Southern Spain). A pattern in snow albedo from all the snow pixel in each Landsat scene was obtained. It ranges from 0.8 in new snow to 0.4 in old dirty snow, with a decreasing rate of 0.003 albedo per day. This trend was validated with 5 specific location, where the snow is more persistent while the pixel remains well-illuminated.

Ecological Indicators, 2014

ABSTRACT Abstract This paper investigates the use of the vegetative state of natural covers as an... more ABSTRACT Abstract This paper investigates the use of the vegetative state of natural covers as an indicator of soil moisture conditions at the end of the dry season in order to evaluate the cumulative effect of the hydrological regime. To achieve this, the three major vegetation covers in a mountainous semiarid environment in southern Spain were selected. Temporal and spatial trends of NDVI from Landsat-TM images were computed and related to the different hydrological patterns of variables in the study site, which were obtained with the hydrological WiMMed model. The heterogeneity in the hydrological behavior during the study period (914.5 mm of annual rainfall in the wettest year (2009–2010) and 284.4 mm in the driest year (2004–2005)) was reflected in the annual differences in NDVI values with steady mean NDVI values in coniferous vegetation (0.5–0.6) and more variable values in scrub cover. Both Correlation Analysis and Principal Component Analysis showed correlations among the different states of the vegetation cover, the variables involved in the soil water balance and those related to the snow dynamics of the antecedent year. Exponential fits were obtained between the mean annual soil water content and NDVI values with Pearson r2 coefficients of over 0.7 in scrub cover. In certain years, the best fits were also found in scrub cover with r2 values of up to 0.9. These results demonstrate the relationship between soil water content, the vigor of the natural vegetation and the hydrological characteristics of the antecedent year. The expressions obtained may serve to adjust the soil water content at the beginning of a hydrological year and to use the scrub cover as an indicator of the soil water balance in the area for a given year.

Remote Sensing for Agriculture, Ecosystems, and Hydrology XIV, 2012

ABSTRACT In Mediterranean regions, where the water shortage is a serious and recurrent problem, i... more ABSTRACT In Mediterranean regions, where the water shortage is a serious and recurrent problem, it is essential to know the behaviour and evolution of the snow. Satellite remote sensing is widely used to find out the evolution of the snow cover extension at medium-large scales. But these techniques pose some constraints if snow is heterogeneously distributed, as they do not correctly represent the physical processes that occur on a smaller scale than the satellite image. In such cases, terrestrial photographs, whose resolution can be more easily adapted to the required resolution for these study cases, are an economic and also efficient alternative. This work presents a methodology for the georeferencing and automatic detection of snow in terrestrial photography, as an alternative to the use of satellite images for the study of the snow cover evolution in small areas. This methodology has been evaluated during the snowmelt period in the spring of 2009 at a study site in Sierra Nevada Natural Park (Southern Spain). The resulting snow maps have been compared with the results available for that period obtained from the analyses of four Landsat images. The results show that the use of Landsat generally overestimated the extension of the snow cover in the study area.

Remote Sensing for Agriculture, Ecosystems, and Hydrology XV, 2013

ABSTRACT The albedo of snow affects the shortwave radiative flux at the land-atmosphere interface... more ABSTRACT The albedo of snow affects the shortwave radiative flux at the land-atmosphere interface, so that it therefore plays an important role in the snow mass and energy balance. In semiarid areas, their particular climate conditions enhance the spatiotemporal variability of the snow albedo during the snow cover periods, increasing its difficulty in being measured and monitored. Satellite remote sensing is a powerful tool for measuring snow albedo evolution. Ten years of Landsat-5 and Landsat-7 Thematic Mapper images were analysed to determine a trend in the albedo evolution throughout the year in a Mediterranean site, Sierra Nevada Mountain (Southern Spain). A pattern in snow albedo from all the snow pixel in each Landsat scene was obtained. It ranges from 0.8 in new snow to 0.4 in old dirty snow, with a decreasing rate of 0.003 albedo per day. This trend was validated with 5 specific location, where the snow is more persistent while the pixel remains well-illuminated.

Journal of chromatography. A, Jan 30, 2003

Headspace solid-phase microextraction, followed by GC-MS analysis is presented as a suitable tech... more Headspace solid-phase microextraction, followed by GC-MS analysis is presented as a suitable technique for the determination of musk compounds in sewage treatment plant sludge. Five polycyclic musks (celestolide, phantolide, traseolide, galaxolide and tonalide) and four nitro musks (musk xylene, musk moskene, musk tibetene and musk ketone) were considered in the optimisation of the analytical method. The influence of extraction temperature, fibre coating, agitation, pH and salting out on the efficiency of the extraction along with the extraction kinetics were studied. An extraction temperature of 100 degrees C and sampling the headspace over the stirred sludge sample using polydimethylsiloxane -divinylbenzene as fibre coating lead to effective extraction. The method proposed is very simple and yields high sensitivity, good linearity and repeatability for all the analytes with limits of detection at the sub-ng/g level. The total analysis time, including extraction and GC analysis, was only 40 min, and no manipulation of the sample was required.

Journal of chromatography. A, Jan 18, 2006

A solid-phase microextraction (SPME) method has been developed for the determination of pentachlo... more A solid-phase microextraction (SPME) method has been developed for the determination of pentachlorophenol (PCP) in paper and board samples. The analytical procedure involves direct extraction of PCP from paper and board samples and determination by gas chromatography with electron capture detection (GC-ECD). Two kinds of commercially available fibres; 100 m polydimethylsiloxane (PDMS), apolar, and 85 m polyacrylate (PA), quite polar, were evaluated to determine the extraction efficiency of pentachlorophenol. Parameters affecting the extraction process, such as temperature and time, were studied. Moreover, time of desorption and the effect of addition of salt were also investigated. The optimized procedure was applied to the analysis of pentachlorophenol (PCP) in five samples of virgin and recycled paper and board. The PCP content was determined by GC-ECD. To evaluate the effectiveness of the proposed method, it was compared with conventional extraction method with liquid-liquid extraction and derivatization. Detection limit of 0.015 g/g for PCP in paper was achieved with a RSD of 14%.

Analytical and bioanalytical chemistry, 2007

A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron ca... more A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron capture detection for determining trace levels of nitro musk fragrances in residual waters was optimized. Four nitro musks, musk xylene, musk moskene, musk tibetene and musk ketone, were selected for the optimization of the method. Factors affecting the extraction process were studied using a multivariate approach. Two extraction modes (direct SPME and headspace SPME) were tried at different extraction temperatures using two fiber coatings [Carboxen-polydimethylsiloxane (CAR/PDMS) and polydimethylsiloxane-divinylbenzene (PDMS/DVB)] selected among five commercial tested fibers. Sample agitation and the salting-out effect were also factors studied. The main effects and interactions between the factors were studied for all the target compounds. An extraction temperature of 100°C and sampling the headspace over the sample, using either CAR/PDMS or PDMS/DVB as fiber coatings, were found to be the experimental conditions that led to a more effective extraction. High sensitivity, with detection limits in the low nanogram per liter range, and good linearity and repeatability were achieved for all nitro musks. Since the method proposed performed well for real samples, it was applied to different water samples, including wastewater and sewage, in which some of the target compounds (musk xylene and musk ketone) were detected and quantified.

Journal of Chromatography A - J CHROMATOGR A, 2005

A solid-phase microextraction method (SPME) coupled to gas chromatography–mass spectrometry (GC–M... more A solid-phase microextraction method (SPME) coupled to gas chromatography–mass spectrometry (GC–MS) has been developed for the determination of the six phthalate esters included in the US Environmental Protection Agency (EPA) Priority Pollutants list in water samples. These compounds are dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), butylbenzyl phthalate (BBP), di-2-ethylhexyl phthalate (DEHP) and di-n-octyl phthalate (DOP). Detailed discussion of the different parameters, which could affect the extraction process, is presented. Main factors have been studied and optimized by means of a multifactor categorical design. Different commercial fibers, polydimethylsiloxane (PDMS), polydimethylsiloxane–divinylbenzene (PDMS–DVB), polyacrylate (PA), Carboxen–polydimethylsiloxane (CAR–PDMS) and Carbowax–divinylbenzene (CW–DVB), have been investigated, as well as the extraction mode, exposing the fiber directly into the sample (DSPME) or into the headspace over the sample (HS-SPME), and different extraction temperatures. The use of this experimental design allowed for the evaluation of interactions between factors. Extraction kinetics has also been studied. The optimized microextraction method showed linear response and good precision for all target analytes. Detection limits were estimated considering the contamination problems associated to phthalate analysis. They were in the low pg mL−1, excluding DEHP (100 pg mL−1). The applicability of the developed SPME method was demonstrated for several real water samples including mineral, river, industrial port and sewage water samples. All the target analytes were found in real samples. Levels of DEP and DEHP were over 1 ng mL−1 in some of the samples.

Journal of the Science of Food and Agriculture, 1992

Abstract: Several multivariate statistical methods (principal component, cluster, stepwise discri... more Abstract: Several multivariate statistical methods (principal component, cluster, stepwise discriminant and multiple linear regression analysis) were applied to analytical data obtained by conventional methods and to analytical data for free amino acids, in an attempt to distinguish between ...

Journal of Environment Quality, 2006

The residual pollution after the Aznalcóllar (southwestern Spain) pyrite mine spill is still a th... more The residual pollution after the Aznalcóllar (southwestern Spain) pyrite mine spill is still a threat due to the continuing oxidation of sulfuric minerals. The objective of this paper was to analyze the combined effect of pyrite oxidation, sugar beet foam applications, and meteorological conditions on the spatiotemporal evolution of the pH and EDTA-extractable Zn concentration, using non co-located data from 11 sampling dates between June 1999 and March 2002. Median pH values ranged from 4.4 at the beginning of the monitoring period to 7.6 at the end, although values near 2.5 were observed throughout the entire period, despite of two sugar beet foam (SBF) applications. Zinc distributions were positively skewed and median concentrations ranged from 17 to 94 mg kg(-1). The inverse relationship between pH and Zn became weaker toward the end of the monitoring period as a consequence of the precipitation and posterior dissolution of newly formed minerals from the reaction products of the pyrite oxidation. Normal score maps showed that after the SBF applications only 0.5% of the monitored area was below the pH = 4 threshold, while on other dates up to one-third of the area remained below this value. The better performance of the second SBF application could be explained in terms of pyrite oxidation pathways and environmental conditions. From this analysis, with data obtained under uncontrolled field conditions, it is concluded that SBF should be applied before or during the wet and cold season to alleviate acidification, caused by the oxidation of pyrite or other sulfuric minerals.

Journal of Environment Quality, 2006

Monitoring of soil chemical properties for pollution assessment generally requires destructive so... more Monitoring of soil chemical properties for pollution assessment generally requires destructive soil sampling and results in spatiotemporal datasets where data from different sampling dates are non co-located. The objective of this study was to assess the spatial distribution of residual pyrite sludge at a reclaimed site, using temporally non co-located data on pH; soil oxidizable fraction (SOF); and EDTA-extractable Fe, Zn, and Cu from six different sampling dates over a period of 2 yr. During this period spatially averaged pH and Zn concentrations ranged, respectively, from 4.4 to 6.6 and from 60 to 140 mg kg(-1), with minimum pH values of below 2.7. The data were merged into a single dataset for each chemical property after applying a normal score (ns) transform. Normal score pH was significantly negatively correlated with the ns metal concentrations. A principal component analysis (PCA) showed that normal score pH, Zn, and Fe were associated with the residual contamination, while ns Cu, SOF, and elevation were related with historic contamination. The spatial dependence between the properties was found to be scale-dependent. The best ns estimates were produced by ordinary kriging with an anisotopic variogram model, for the properties related with Principal Component (PC) I, while those associated with PC II were best estimated using simple kriging with varying local means. A classified ns pH map showed that 33% of the study area reached at least once values of below 4 during the 2-yr period. This part of the area should be excluded to ensure successful revegetation.

Journal of Chromatography A, 2006

A depletion solid-phase microextraction (SPME) method based on multiple SPME extraction was appli... more A depletion solid-phase microextraction (SPME) method based on multiple SPME extraction was applied to estimate fibre coating-water distribution constants (Kfs) of brominated flame retardants. Several polybrominated diphenyl ethers (PBDEs) including compounds present in the commercial mixture "Pentamix", and two polybrominated biphenyls (PBBs) were considered as target analytes. One hundred-micrometer poly(dimethylsiloxane) (PDMS) coating fibre was selected to estimate partition coefficients. SPME kinetics studies at 25 and 100 degrees C were performed. Kfs values obtained at both temperatures for brominated flame retardants were compared with the corresponding octanol-water partition coefficients (Kow) values found in literature. A linear log-log relationship between Kow with Kfs was found. To the best of our knowledge, this is the first study where brominated flame retardants Kfs values are estimated.

Journal of Agricultural and Food Chemistry, 2004

The anthocyanin pigments in rosé (Vitis vinifera cv. Garnacha) and blanc de noir (V. vinifera cv.... more The anthocyanin pigments in rosé (Vitis vinifera cv. Garnacha) and blanc de noir (V. vinifera cv. Monastrell) base and sparkling wines were studied by LC-DAD/ESI-MS. Anthocyanins of grape origin and pyranoanthocyanins resulting from C-4/C-5 cycloaddition of the former ones with pyruvic acid, acetaldehyde, 4-vinylphenol, 4-vinylguaiacol, and 4-vinylcatechol were identified in the different wines. Rosé wines presented a higher total pigment content than blanc de noir wines. Pyranoanthocyanins represented 68.9-76.0% of total pigment content in rosé wines and 49.4-60.7% in blanc de noir wines. Malvidin 3-glucoside-pyruvate was the most abundant pigment in both rosé and blanc de noir base wines. Important qualitative and quantitative changes were observed in terms of the anthocyanin and pyranoanthocyanin pigments after the second (bottle) fermentation and 9 months of aging on yeast lees, but not after a further time (3-9 additional months) of aging on lees. Evaluation of the wine color characteristics was consistent with a greater color stability for the rosé sparkling wines that could be associated with the high content, structural diversity, and spectroscopic features of the pyranoanthocyanins present in these wines.

Clinical Neurophysiology, 2003

Objective: Increased distractibility is a common impairment in alcoholism, but objective evidence... more Objective: Increased distractibility is a common impairment in alcoholism, but objective evidence has remained elusive. Here, a task designed to investigate with event-related brain potentials (ERPs) the neural mechanism underlying distraction was used to show abnormal involuntary orienting of attention in chronic alcoholism.

Analytical and Bioanalytical Chemistry, 2007

A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron ca... more A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron capture detection for determining trace levels of nitro musk fragrances in residual waters was optimized. Four nitro musks, musk xylene, musk moskene, musk tibetene and musk ketone, were selected for the optimization of the method. Factors affecting the extraction process were studied using a multivariate approach. Two extraction modes (direct SPME and headspace SPME) were tried at different extraction temperatures using two fiber coatings [Carboxen-polydimethylsiloxane (CAR/PDMS) and polydimethylsiloxane-divinylbenzene (PDMS/DVB)] selected among five commercial tested fibers. Sample agitation and the salting-out effect were also factors studied. The main effects and interactions between the factors were studied for all the target compounds. An extraction temperature of 100°C and sampling the headspace over the sample, using either CAR/PDMS or PDMS/DVB as fiber coatings, were found to be the experimental conditions that led to a more effective extraction. High sensitivity, with detection limits in the low nanogram per liter range, and good linearity and repeatability were achieved for all nitro musks. Since the method proposed performed well for real samples, it was applied to different water samples, including wastewater and sewage, in which some of the target compounds (musk xylene and musk ketone) were detected and quantified.