C. D. Arbelo

Testing the validity of a Cd soil quality standard in representative Mediterranean agricultural soils under an accumulator crop

The validity of a quality standard for cadmium (Cd) in representative agricultural Mediterranean soils under an accumulator crop (Lactuca sativa L.) is evaluated in this work considering both its effect on the crop growth (biomass production) and the metal accumulation in the edible part of the plant. Four soils with different properties relevant to regulate the behaviour of heavy metals were selected from the Valencian Region, a representative area of the European Mediterranean Region. For all soils, the effective concentration of added Cd causing 50% inhibition (EC(50)) on the biomass production was much higher than the minimum legal concentration used to declare soils as contaminated by cadmium, i.e. 100 times the baseline value for Cd, in Spain (Spanish Royal Decree 9/2005). As expected, Cd toxicity in the crop was higher in the soils having less carbonate content. On the other hand, for all soils, from the second dose on, which represents 10-times the baseline value for Cd, the metal content in crops exceeded the maximum level established for leaf crops by the European legislation (Regulation EC no. 466/2001). Soil salinity and coarse textures make the accumulation of Cd in the edible part of the plant easier. Therefore, the legal baseline soil cadmium content established by the Spanish legislation seems not valid neither from the point of view of the effect on the crop growth nor from the point of view of the metal accumulation in the edible part of the plant. In order to realistically declare contaminated soils by heavy metals, soil quality standards should be proposed taking into account the soil properties. Further research in other agricultural areas of the region would improve the basis for proposing adequate soil quality standards for heavy metals as highlighted by the European Thematic Strategy for Soil Protection.

Interannual variations of soil organic carbon fractions in unmanaged volcanic soils (Canary Islands, Spain)

The stability over time of the organic C stocked in soils under undisturbed ecosystems is poorly studied, despite being suitable for detecting changes related to climate fluctuations and global warming. Volcanic soils often show high organic C contents due to the stabilization of organic matter by short-range ordered minerals or Al-humus complexes. We investigated the dynamics of different organic C fractions in volcanic soils of protected natural ecosystems of the Canary Islands (Spain) to evaluate the stability of their C pools. The study was carried out in 10 plots, including both undisturbed and formerly disturbed ecosystems, over two annual periods. C inputs to (litterfall) and outputs from (respiration) the soil, root C stocks (0–30 cm), soil organic C (SOC) fractions belonging to C pools with different degrees of biogeochemical stability –total oxidisable C (TOC), microbial biomass C (MBC), water soluble C (WSC), hot-water extractable C (HWC), humic C (HSC), – and total soil N (TN) (at 0–15 and 15–30 cm) were measured seasonally.A statistically significant interannual increase in CO2 emissions and a decrease in the SOC, mainly at the expense of the most labile organic forms, were observed, while the root C stocks and litterfall inputs remained relatively constant over the study period. The observed changes may reflect an initial increase in SOC resulting from low soil respiration rates due to drought during the first year of study. The soils of nearly mature ecosystems were more apparently affected by C losses, while those undergoing the process of active natural regeneration exhibited disguised C loss because of the C sequestration trend that is characteristic of progressive ecological succession.

Effects of a Canary pine forest wildfire (Tenerife, Canary Islands, summer 2007) on selected soil properties and their relationship with short- to medium-term soil water repellency .

Forest fires modify the soil environment, often triggering severe soil degradation. In this paper, we studied the impact of a large northern Tenerife Canariy pine forest wildfire on a set of relevant soil properties, focusing on their evolution in time and relationship with soil water repellency. To do this, soils were sampled at four sites (burned and non-burned) and several soil physical and chemical parameters were measured. The results show significant variations for soil pH, electric conductivity (CE 1:5 ), and NH 4 + -N between burned and non-burned samples, whereas non-significant increases were found in burned soils for oxidizable carbon (C ox ), total nitrogen (N tot ) , Ca 2+ , Mg 2+ , Na + and K + , and soil hydrophobicity. The differences caused by the fire were no longer evident one year later. Furthermore, in one sampling site (Vitric Leptosols under low pine forest with a mixed heath/beech tree understory) a wide variation in the content of C ox and N tot and high water repellency was observed relative to the other sites. These differences can be attributed to the composition of the understory vegetation. Significant correlations between soil hydrophobicity with CE 1:5 , aggregate stability and the contents of C ox , N tot , NH 4 + -N, Ca 2+ , Mg 2+ , Na + and K + were found.

Evolutive and regressive soil sequences for characterization of soils in laurel forest (Tenerife, Canary Islands) .

Los procesos de degradacion del suelo han alcanzado en los ultimos anos el reconocimiento de problema ambiental global y ha sido sugerido desde diversos foros y organismos internacionales que, para establecer de manera adecuada metodos de lucha contra la degradacion de los suelos, es necesario evaluar esta degradacion a nivel local y a escala detallada. La evaluacion de la degradacion de los suelos de los ecosistemas naturales a escala detallada requiere la definicion de estandares ante los que comparar esta degradacion. Para definir estos estandares y manejar adecuadamente los procesos que dan lugar a variaciones en la calidad de los suelos y en su degradacion, se necesita establecer con cierto detalle los procesos edafogenicos que tienen o han tenido lugar en un area determinada y que llevan a la formacion de un suelo maduro, al cual debe considerarse como estandar en estas situaciones y por tanto como suelo no degradado. De acuerdo con estas ideas, en este trabajo presentamos las posibles sucesiones evolutivas y regresivas de los suelos y algunos ejemplos del uso de esta metodologia para evaluar la degradacion de los mismos en el Monteverde de la isla de Tenerife (Islas Canarias, Espana). Se presentan ademas algunas caracteristicas fisicas, quimicas y mineralogicas de suelos climacicos maduros, suelos degradados y suelos de baja calidad y sus analogias y diferencias en este entorno bioclimatico y para diferentes materiales parentales. Asi, se observa, que los principales procesos de degradacion de suelos en estas zonas estan ligados a modificaciones de la cubierta vegetal, que llevan a la disminucion de la proteccion de la superficie del suelo que tiene como consecuencia, a largo plazo, el desencadenamiento de procesos de degradacion tales como: erosion hidrica, degradacion biologica, perdida de las propiedades andicas, compactacion y formacion de costras de sellado superficial, perdida de la capacidad de retencion de agua, iluviacion, etc. Los suelos climacicos que podemos encontrar en las zonas de coladas y de fuerte pendiente son Leptosoles, mientras que en las zonas de pendientes suaves aparecen Cambisoles y Andosoles. Sobre los materiales piroclasticos nos encontramos con Andosoles vitricos y Andosoles andicos, segun su grado de evolucion. Los procesos regresivos mas caracteristicos son la argiluviacion/lixiviacion, que dan lugar a Luvisoles, Lixisoles y Alisoles, y la erosion hidrica, causante de la presencia de Leptosoles secundarios.

Criterios y recomendaciones para la toma de imágenes de perfiles de suelos para crear una base de datos de imágenes .

El objetivo de este trabajo es mejorar las habilidades de los cientificos de suelos en la toma de imagenes de suelos para la docencia y la publicacion de trabajos cientificos. Los autores han compilado un conjunto de instrucciones, recomendaciones y consejos a partir de su experiencia, que van desde la captura de imagenes a la seleccion de un formato de archivo apropiado para almacenar o publicar una imagen, pasando por la edicion y el post-procesado de las imagenes. Los aspectos principales incluidos en este trabajo se refieren a la posicion fisica de la camara cuando se dispara para tomar un perfil de suelo, el ajuste basico de la camara, las acciones basicas de retoque y una lista de recomendaciones y errores que deben evitarse.