Departamento de Cristalografía, Mineralogía y Química Agrícola. Facultad de Química. Universidad de Sevilla. C/profesor García González, 1 41010 - Sevilla Spain
Abstract: Soil water repellency has been conventionally considered as a fire-induced effect, but an increasing number of works have suggested that natural background repellency occurs in many soil types, and many of them have suggested that water repellency can re-establish a time after being destroyed. An experimental fire was conducted to study changes of the soil surface during the first 18 months following intense burning. The main objectives of this paper are: [1] to investigate in situ water repellency changes at three soil depths (0, 2 and 4 cm) immediately after burning, [2] to evaluate the medium-term evolution of water repellency under field conditions, and [3] to outline the main hydrological consequences of these changes. Also, different water repellency tests (water drop penetration time, ethanol percentage test and contact angle between water drops and soil surface) were carried out with comparative purposes. Field experiments showed that soil water repellency soil water repellency was partly destroyed after intense burning. Changes were relatively strong at the soil surface, but diminished progressively with depth. Levels of water repellency were practically re-established 18 months after burning. This suggests that water repellency in the studied area is not necessarily a consequence of fire, but can instead be a natural attribute. Finally, although limited in time, destruction of soil water repellency has important consequences for runoff flow generation and soil loss rates, and, indirectly, for water quality.
Abstract: The distribution and variation with soil depth of water repellency has been studied in fire-affected sand dunes under three different vegetation types (pine forest, shrubland and sparse herbaceous vegetation) in SW Spain. The persistence and intensity of water repellency at the exposed surface of soil was measured using the water drop penetration time test and the contact angle method, respectively, in surface samples (0- 3 cm) collected at burned and unburned areas. The variation of water repellency with depth in burned areas was studied in soil profiles every 5 cm between 0 and 40 cm depth. None or slight soil water repellency was observed at unburned soil sites, whereas burned soil sites showed a high degree of repellency, especially under pines and shrubland. The spatial pattern of fire-induced soil water repellency was found to be associated to vegetation types, although it was modulated by soil acidity and the soil organic carbon content. Soil water repellency was generally higher at the soil surface, and decreased with depth. Dense pine forests and shrublands showed strong and/or severe water repellency in depth, but it was rare and limited to the first five centimeters under sparse herbaceous vegetation. The heterogeneity of moisture patterns under dense pine forests or shrublands showed the existence of wetting and water repellent three-dimensional soil patches.
Abstract: The objectives of this research are the following: [1] to study the persistence and intensity of water repellency in soil samples (0-5 cm deep) collected under different plant species, [2] to analyze the relationships between soil water repellency and environmental factors including soil organic matter content, soil acidity, and texture, and [3] to study the variations of soil water repellency measured on soil samples collected in winter (2007) and summer (2008) in the studied area. Soil water repellency has been studied in Mediterranean coniferous and eucalyptus forests, particularly after burning, but the number of studies concerning other Mediterranean forest systems is still very low. In this paper, soil water repellency was measured by using the water drop penetration time test and the ethanol percentage test on samples collected during the winter of 2007 and the summer of 2008 under different land uses (pines, cork oaks, eucalyptus, heathland and olive trees) in a Mediterranean subhumid forested area (Los Alcornocales Natural Park, C 225;diz and M 225;laga, Spain). Most of soil samples collected under heathland showed extreme water repellency, whereas soils under olive trees showed low or inexistent water repellency. The organic matter content and acidity were highly correlated with water repellency in soils under pines, cork oaks and eucalyptus, while soils under heathland or olive trees showed poorer correlations. The average soil moisture content of samples collected during winter (2007) was 20.7 177;7.9 %, and it decreased in samples collected during summer (2008) to 1.1 177;0.6 %. The persistence and intensity of water repellency varied slightly between samples collected in winter and summer in soils under all species except under heathland. Water repellency persisted in most cases during the wet and dry season, and many soils showed strong water repellency even during winter. The patchy patterns of persistence and intensity of soil water repellency is conditioned by the spatial distribution of the studied land uses, which dictate the intensity and persistence of soil water repellency, and modulated by other environmental factors. The vegetation effects on soil hydrology should be considered for afforestation work and flooding control.
Abstract: The dynamics of land use changes between 1956 and 2003 in the coastal fringe of C 225;diz province (Southern Spain) are discussed in relation to urban development, population and other factors. The analysis of the main land uses with a geographic information system shows the effects of recent farming technologies and regional agricultural or environmental policies, besides other processes, as the development of mass tourist projects and urban expansion. Buffers from specific variables (distance to roads, gravel pits/mining areas, reservoirs and urban settlements) have been used to assess transformation patterns and identify potential causes of land use change. The most important land use changes in the studied area are due to the growing and concentration of population in the cities, the coastal mass tourism, the development of infrastructures such as roads or reservoirs, and the agricultural policies that encourage the substitution of traditional rain-fed crops with irrigated crops during the second part of 20th century. The increment of productivity due to the transformation of rain-fed crops into irrigated crops is weakly related to soil capability. A part of the agricultural expansion has been observed in marginal soils, probably because of the increase in technological inputs. The loss of agricultural soil per capita in the studied area appears to be associated to an improvement of farming technologies and the lack of relationships between population and local agricultural products in a globalized context. En el presente trabajo se discute la din 225;mica de los cambios de uso entre 1956 y 2003 en la franja costera de la provincia de C 225;diz en relaci 243;n con el desarrollo urbano, la poblaci 243;n y otros factores. El an 225;lisis de los principales usos del terreno mediante un sistema de informaci 243;n geogr 225;fica muestra los efectos del desarrollo de la tecnolog 237;a agr 237;cola y las pol 237;ticas regionales agr 237;colas o medioambientales, adem 225;s de otros procesos como el desarrollo de proyectos de turismo de masas o la expansi 243;n urbana. Para estudiar los patrones de transformaci 243;n e identificar causas potenciales de cambio se han determinado 225;reas de influencia de variables espec 237;ficas (distancia a las carreteras, graveras/minas, embalses y asentamientos urbanos). Los cambios de uso m 225;s importantes en el 225;rea se deben al crecimiento y concentraci 243;n de la poblaci 243;n en las ciudades, el turismo costero, el desarrollo de infraestructuras como carreteras o embalses y las pol 237;ticas agr 237;colas que promueven el cambio del secano tradicional por regad 237;os durante la segunda mitad del siglo XX. El incremento de la productividad debido a la transformaci 243;n de secanos en regad 237;os no muestra gran relaci 243;n con la apacidad de uso del suelo. Una parte de la expansi 243;n agr 237;cola ha ocurrido sobre suelos marginales, probablemente a causa del incremento en el input tecnol 243;gico. La p 233;rdida de suelo agr 237;cola per capita en el 225;rea de estudio parece estar asociado a una mejora en las tecnolog 237;as agr 237;colas y la falta de relaciones entre la poblaci 243;n y la producci 243;n agr 237;cola local en un contexto globalizado.
Abstract: In this paper five soil profiles of a toposequence located on âSierra de Algodonalesâ (SW Spain) have been studied; developed on limestones rocks of the Jurassic Period. In that sequence they are distinguished leptosols, calcisols, kastanozems and luvisols. Special emphasis in the nature of the clayey fraction and in the mineralogical forms of the iron is done. The fraction clay of these soils has been used like an evolution index and smectite, kaolinite, vermiculite and illite, with small quantities of mixed-layer illite-vermiculite and illite-smectite have been found in this study. The fractions of total iron (Fe_t), iron extracted with dithionite (Fe_d) and iron extracted with oxalate (Fe_o) have been use as an index to differentiate the evolution of the horizons of the studied soils.
Abstract: The main objective of this paper is a detailed analysis of the physical environment of the Tepalcatepec River basin (through the states of Jalisco and Michoacan, Mexico) as a previous stage to an erosion risk map. We have used an classification system modified from Dikau et al. (1991). The results obtained let us to divide the basin of the Tepalcatepec River in five classes of main geoforms. Each class has been divided in several subclasses, so that 17 land units have been distinguished. The results show that the used method allows to identify accurately the existing land forms, and with much greater detail, an elevated number of subclasses.
Abstract: The decadence of mining activity in the Riotinto Mining District (SW Spain) during the end of the last century has led to the citrus agriculture as the new social development. This new activity has been carried out around abandoned mines without the assessment of soil pollution. The aim of this work is to study the distribution of potentially toxic elements in soils of the Riotinto mining area and compare them with the element concentration absorbed by plants, in order to assess the potential risk involved in the use of the studied soils, defining also the most dangerous areas for agricultural activities. Twenty-seven agricultural soil samples were collected from the Riotinto area. Major and trace elements were analysed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) after 4 acid (HFâHClO4âHNO3âHCl) digestion, except As, Co and Cr that were analyzed by Instrumental Neutron Activation Analysis (INAA). In general the total concentrations of the trace elements analysed exceeded the background concentration values for Andalusian soils and, on occasions, they surpassed the threshold values defined by percentile 95 for the geological domain of the South Portuguese Zone (Galán et al., 2008). Copper and Zn displayed median values of 99 and 150 mg/kg, respectively, and 44% of the samples surpassed the threshold of 147 and 173 mg/kg for Cu and Zn, respectively. Arsenic reached up to 204 mg/kg and Pb up to 598 mg/kg. The association As-Cu-Pb-Zn and their distribution close the Riotinto waste dumps (NE of the studied area) suggests an anthropogenic origin for these elements. On the contrary, Ni, Cr and Co showed also high values with median concentrations of 41, 113 and 23 mg/kg, respectively, but about 30-48% of the samples were below the baseline values proposed for these elements. The distribution of Fe-Co-Cr-Ni shows they are enriched in the SW part associated to volcanic rocks, which suggests a geogenic origin for them. In order to evaluate the potential risk, the bioavailability was assessed by acidic and EDTA extractions. Copper, Zn and Pb showed a high bioavailability in several samples of the NE part, which involve a high potential risk for agriculture in this zone. On the other hand, Co, Cr and Ni showed a low bioavailability even when they displayed high total concentration in soils. The foliar analysis of orange trees was carried out by ICP mass spectroscopy (ICP-MS), and it showed that not always bioavailable elements were absorbed by plants.
Abstract: The occurrence of water repellency is common in surface horizons from Mediterranean soils during and immediately after the dry season. Several researchers have highlighted the important role played by certain plant species in developing soil water repellency, although it cannot be assumed that these species always induce water repellency under natural conditions. Water repellency has been often described in the surface of dune sands. Water repellency in sandy soils develops as a consequence of sand particles coated with organic substances produced by fungal activity. Partially decomposed plant parts directly contribute to the development of water repellency in soils. Although the organic matter content of water repellent soils can be very low, the presence of organic substances as humic acids can induce soil hydrophobicity. Some of the consequences of soil water repellency are reduced soil infiltration rates, enhanced runoff flow and soil erosion. The importance of these effects depends upon the severity and spatial variability of hydrophobicity. Some authors have reported unstable wetting fronts in water repellent soils, in contrast with wettable soils, where water can infiltrate forming an uniform horizontal wetting front. However, water repellent soils will get wet after prolonged or recurrent rainfall, what results in a ponded and very wet topsoil layer resting on relatively dry and/or still water repellent soil body. In such case, infiltrated water may flow following different paths. In a water repellent soil body, water may flow laterally, and provide water to places where vertical flow paths are formed, resulting in fingered infiltration. These vertically directed preferential flow paths facilitate the rapid movement of water and solutes to the groundwater. Preferential flow paths create spatial variability in soil moisture affecting plant growth. The distribution and variation with soil depth of water repellency has been studied in fire-affected sand dunes under three different vegetation types (pine forest, shrubland and sparse herbaceous vegetation) in SW Spain. The persistence and intensity of water repellency at the exposed surface of soil was measured using the water drop penetration time test and the contact angle method, respectively, in surface samples (0- 3 cm) collected at burned and unburned areas. The variation of water repellency with depth in burned areas was studied in soil profiles every 5 cm between 0 and 40 cm depth. None or slight soil water repellency was observed at unburned soil sites, whereas burned soil sites showed a high degree of repellency, especially under pines and shrubland. The spatial pattern of fire-induced soil water repellency was found to be associated to vegetation types, although it was modulated by soil acidity and the soil organic carbon content. Soil water repellency was generally higher at the soil surface, and decreased with depth. Dense pine forests and shrublands showed strong and/or severe water repellency in depth, but it was rare and limited to the first five centimeters under sparse herbaceous vegetation. The heterogeneity of moisture patterns under dense pine forests or shrublands showed the existence of wetting and water repellent three-dimensional soil patches.
Abstract: En este trabajo se ha estudiado la importancia del efecto de la capa de hojarasca quemada y de cenizas sobre la hidrofobicidad del suelo, la generaci 243;n de escorrent 237;a y la erosi 243;n en el per 237;odo inmediatamente posterior a un incendio experimental en un brezal de la Sierra de Algeciras (C 225;diz). Se realizaron ensayos de lluvia simulada con una intensidad de 70 mm/h durante 60 minutos en 21 puntos dentro del 225;rea experimental de la siguiente manera: previamente al incendio, se realizaron 21 simulaciones en puntos marcados con barras verticales met 225;licas; durante la semana posterior al incendio y en puntos alejados 50 cm de las marcas, se realizaron 21 simulaciones sobre la hojarasca, 21 simulaciones retirando la hojarasca y 21 simulaciones retirando la hojarasca y la ceniza; finalmente, un a 241;o despu 233;s del incendio se realizaron 21 simulaciones en los puntos marcados. En cada caso se recogi 243; la escorrent 237;a para medir la tasa de infiltraci 243;n y la p 233;rdida de sedimentos y se anot 243; el tiempo transcurrido hasta el encharcamiento y aparici 243;n de la escorrent 237;a. Posteriormente al incendio, en cada punto se determin 243; la profundidad de la capa de cenizas y de hojarasca quemada y se analiz 243; la hidrofobicidad del suelo seg 250;n el m 233;todo de tiempo de penetraci 243;n de la gota de agua (WDPT). Los resultados mostraron que la persistencia de una gruesa capa de hojarasca y cenizas durante el per 237;odo posterior a un incendio no contribuye a aumentar la escorrent 237;a o el riesgo de erosi 243;n del suelo. Sin embargo, cuando la superficie del suelo queda expuesta, la erodibilidad puede incrementarse de manera apreciable. De ese modo, cuando la capa de cenizas es dispersada por la lluvia o el viento, las tasas de escorrent 237;a y erosi 243;n pueden incrementarse en uno y dos 243;rdenes de magnitud, respectivamente, especialmente despu 233;s de un evento de lluvia intensa. El incremento de la vegetaci 243;n natural un a 241;o despu 233;s del incendio pr 225;cticamente restableci 243; las condiciones iniciales en todas las variables. El fuego redujo la hidrofobicidad del suelo durante la semana posterior al incendio. Despu 233;s de un a 241;o, este par 225;metro volvi 243; pr 225;cticamente a los valores iniciales. La persistencia de la hojarasca y los residuos org 225;nicos en el suelo tras un incendio de baja severidad y la redistribuci 243;n de sedimentos de 225;reas vecinas tras la estaci 243;n lluviosa pueden explicar este restablecimiento.
Abstract: El objetivo del presente trabajo es estudiar la g 233;nesis e interacciones entre suelos mediterr 225;neos en una toposecuencia sobre materiales calc 225;reos jur 225;sicos (calizas y dolom 237;as) y sobre una geomorfolog 237;a anticlinoria, con retoques k 225;rsticos y puntualmente periglaciares en la Sierra de Algodonales (C 225;diz). Con esta finalidad se tomaron cinco perfiles siguiendo una ladera con direcci 243;n NW-SE del macizo, Las muestras una vez secas y tamizadas, fueron sometidas a las determinaciones f 237;sico- qu 237;micas generales. As 237; mismo, se identificaron los minerales de arcilla eliminado previamente la materia org 225;nica con per 243;xido de hidr 243;geno al 6% (v/v) y los carbonatos con 225;cido ac 233;tico diluido (0.5N). Posteriormente, se separ 243; la fracci 243;n de arcilla fina ( 60;1.2μm) que fue saturada con cloruro magn 233;sico, difract 225;ndose los agregados orientados secos al aire y saturados con etilenglicol (EG), y con cloruro pot 225;sico, calcinadas a continuaci 243;n a 550 186;C. Los perfiles se clasificaron como Leptosoles l 237;tico-m 243;licos, Kastanozems c 225;lcicos y luvic 225;lcicos y Luvisoles cromi-epil 233;ticos (Figura 1). Los Leptosoles se encuentran tanto en las laderas de pendientes elevadas como en la parte somital del macizo, como respuesta a los intensos procesos erosivos. Los Kastanozems c 225;lcicos y Kastanozems luvi-c 225;lcicos se desarrollan bajo vegetaci 243;n densa de matorral y matorral con querc 237;neas, pero en el caso de los primeros la pendiente es m 225;s acusada. Los Luvisoles se encuentran en inclusiones a media ladera, sin guardar relaci 243;n con la toposecuencia y ocupando bolsadas dejadas en las rocas por los agentes erosivos. La aparici 243;n de inclusiones de Luvisoles cr 243;micos es frecuente en climas mediterr 225;neos sobre caliza dura que han estado sometidas a per 237;odos m 225;s h 250;medos que los actuales. Ello ha permitido que el perfil se encuentre totalmente descarbonatado y que posteriormente haya desarrollado un horizonte de acumulaci 243;n de arcilla (Bt) con un 30% de caolinita posiblemente neoformada. Por otro lado, parece que el Kastanozem luvi-c 225;lcico es el resultado de un proceso poligen 233;tico, debido a que en una primera etapa pose 237;a los mismos caracteres que el anterior; pero posteriormente ha desarrollado un horizonte m 243;lico y acumulaci 243;n de carbonato de calcio en el horizonte Bt.
