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Natural landscapes are spatial-temporal ensembles of landforms and species in interaction with their physical environment. Ecosystems are simply their arbitrary, yet coherent subsets, where the individual components are grouped into functional compartments linked by energy and matter transfer and species interaction. Ecosystems can only persist through a cascade of energy, from higher levels (e.g., solar radiation) to heat, where multiple forms of work can be performed, and without any further work, can only dissipate. Because ecosystems must increase their organization to prevent such an inexorable flow towards degradation and disorder, we say that they can only exist far from equilibrium.

Badlands are landforms that occur all over the World. In the Mediterranean region, badlands are found in both dry (arid and semi‐arid) and wet (subhumid and humid) environments, and are characterized by complex hydro‐geomorphological dynamics, high intense erosion processes and extreme sediment yield. Understanding the impact of Global Change is key to predict the on‐site and off‐site effects on badland dynamics, particularly its consequences on bedrock weathering, on sediment yield and delivery and on plant colonization. Here, conducting a systematic literature review, we analyzed an extensive database and identified the main climate‐drivers affecting the hydro‐geomorphological dynamics in Mediterranean badlands (based on non‐metric multidimensional scaling and structural equation modeling analysis). Later, we examined the main impacts expected from climate change forecasting in the near future, and we explored the interactions between badlands response to climate variation. In Mediterranean badlands, weathering processes are mainly related to wetting–drying cycles and freeze–thaw cycles in dry and wet badlands, respectively. In both environments, rainfall amount appears as the main driver for runoff response, and rainfall amount and rainfall intensity for erosion dynamics. Future climate scenarios forecast a decrease in annual rainfall, number of rainfall events and frost days, and in soil moisture, and an increase in rainfall intensity. These changes will have direct hydro‐geomorphological implications with direct and indirect effects on badland dynamics. This may result in a decrease in annual runoff in dry badlands, but the occurrence of more frequent extreme events would increase soil erosion and could negatively affect biological soil crust. In wet badlands, weathering and erosion processes may decrease, and a stabilization of the slopes, with consequently improved vegetation growth, may be expected. In addition, the forecasted changes must be taken into acco

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Arid and semi-arid ecosystems are characterized by patchy vegetation and variable resource availability. The interplant spaces of these ecosystems are very often covered by cyanobacteria-dominated biocrusts, which are the primary colonizers of terrestrial ecosystems and key in facilitating the succession of other biocrust organisms and plants. Cyanobacterial biocrusts regulate the horizontal and vertical fluxes of water, carbon and nutrients into and from the soil and play crucial hydrological, geomorphological and ecological roles in these ecosystems. In this paper, we analyze the influence of cyanobacterial biocrusts on water balance components (infiltration-runoff, evaporation, soil moisture and non-rainfall water inputs (NRWIs)) in representative semiarid ecosystems in southeastern Spain. The influence of cyanobacterial biocrusts, in two stages of their development, on runoff-infiltration was studied by rainfall simulation and in field plots under natural rainfall at different spatial scales. Results showed that cover, exopolysaccharide content, roughness, organic carbon, total nitrogen, available water holding capacity, aggregate stability, and other properties increased with the development of the cyanobacterial biocrust. Due to the effects on these soil properties, runoff generation was lower in well-developed than in incipient-cyanobacterial biocrusts under both simulated and natural rainfall and on different spatial scales. Runoff yield decreased at coarser spatial scales due to re-infiltration along the hillslope, thus decreasing hydrological connectivity. Soil moisture monitoring at 0.03 m depth revealed higher moisture content and slower soil water loss in plots covered by cyanobacterial biocrusts compared to bare soils. Non-rainfall water inputs were also higher under well-developed cyanobacterial biocrusts than in bare soils. Disturbance of cyanobacterial biocrusts seriously affected the water balance by increasing runoff, decreasing soil moisture and

El objetivo de este proyecto ha sido analizar el contenido en gluten en diferentes tipos de panes comercializados en España. El gluten está relacionado con varias intolerancias: celiaquía, alergias y sensibilidad al gluten no celíaca. La celiaquía, enfermedad autoinmune, se caracteriza por una inflamación de la mucosa del intestino delgado consecuencia de la ingestión de gluten. Estas intolerancias se han incrementado en los últimos años. Entre las causas de este incremento se ha sugerido el elevado contenido en gluten de las harinas. Este estudio se ha realizado en panes tipo Baguette, Barra gallega (barra artesana o chapata), pan integral, pan de espelta y pan de centeno. Los tipos de panes fueron seleccionados de los supermercados: Aldi, Mercadona, Carrefour, Lidl e Hipercor. Para llevar a cabo este proyecto, se trocearon las muestras de pan, se deshidrataron y se obtuvo el peso seco. Una vez molidas, a partir de la harina obtenida se cuantificó el gluten mediante HPLC de fase reversa y mediante el anticuerpo monoclonal R5 (Estándar de referencia del CODEX alimentario). Los datos obtenidos mostraron que todos los panes contienen gluten por encima del valor de referencia de 20 ppm (20 mg/kg = 20 ug/g) para ser apto para celíacos. Se observa una buena correlación entre los valores medidos por el HPLC y el R5 para los panes tipo baguette, barra artesana y barra integral, pero no para los que contienen espelta y especialmente los que contienen centeno. En este último caso, los valores medidos por R5 son muy superiores a los del HPLC. En general, en los productos de todos los supermercados se observa esta tendencia, como ejemplo ponemos los cinco productos de Mercadona, dónde se observa perfectamente la correlación mencionada. Al comparar el contenido en gluten, tanto por HPLC y por R5, se obtuvo que la baguette, barra artesana y barra integral tienen en promedio el mismo contenido en gluten para ambos tipos de cuantificación. Los panes que contienen centeno son los q

Aims: A possible approach to restore drylands is to recover biocrusts by inoculating cyanobacteria. Many studies have demonstrated the ability of cyanobacteria to successfully colonize soil and improve its functions. However, most studies have focused on the abiotic factors influencing the inoculation success, overlooking biotic factors. We examined the influence of the soil indigenous community on the inoculated cyanobacteria by sterilizing soils and analyzing its effects on several key soil properties. Methodology: Nostoc commune was inoculated under laboratory conditions on two soil types with different levels of degradation and under two watering frequencies. All treatments were carried out in natural and sterilized soils. Results: The analysis of the cyanobacterial coverage (30–50% in all inoculated soils), chlorophyll a, visible albedo, roughness, water repellency, organic carbon (OC) and exopolysaccharides (EPS) content showed that cyanobacterial inoculation succeeded, improving soil properties that varied depending on the soil type. The sterilization of soils had little effect: in less degraded soils, the results suggest a faster growth of the indigenous community reaching coverage values of 10% and an interaction with the inoculum that led to a decrease in 2 and 0.3 g Kg of OC and TB-EPS, respectively; in more degraded soils, the community reduced the cyanobacterial coverage around 11%, suggesting competitive interactions. Conclusions: N. commune can be employed to restore lifeless soils. Also, the analysis of native soil community should be considered before field inoculation to plan appropriate methodologies.

Biological soil crust, or biocrust communities, are the dominating life form in many extreme habitats, such as arid and semiarid badlands, where water scarcity and highly erodible substrates limit vegetation cover. While climate, soil and biotic factors have been described as environmental filters influencing biocrust distribution in such biomes, little is known about the effect of terrain attributes on creating specific microhabitats that promote or restrict biocrust colonization. This study aimed to identify the main terrain attributes controlling biocrust distribution in the driest badland system in Europe, the Tabernas Badlands (SE Spain). To do this, we analysed the influence of different terrain attributes related to landscape stability and microclimate formation on the spatial distribution of lichen and cyanobacteria, using field measurements and topographical information from a LiDAR survey. Our results showed that the spatial distribution of cyanobacteria-dominated biocrusts, which are physiologically and morphologically adapted to extreme drought and high UVA radiation, was mostly associated with areas of high potential incoming solar radiation. The exception was bare south-aspect hillslopes with very high sediment transport potential, where bare physically crusted soils were the dominant ground cover. Lichen-dominated biocrusts, in contrast, colonized near the top of north-aspect hillslopes, characterized by low potential incoming solar radiation and potential evapotranspiration, and their cover decreased downstream, as conditions became good enough for vascular plants. © 2019 John Wiley & Sons, Ltd.

Runoff processes are of paramount importance in badland systems which act as runoff sources with significant effects on and off-site. Badland surfaces are highly dynamic in space and time, generating a wide variety of interacting factors and processes that determine runoff generation and flow paths. Understanding these runoff generation processes is critical to answering basic issues in badlands, such as water erosion and flash flood generation, and will further increase our ability to predict runoff and its off-site effects under the impact of future climate and land use. A global perspective of the factors and processes and the interactions driving badland runoff response and its variability are described here. The main impacts expected from forecast climate change on badland runoff under the different conditions in which badlands exist are also examined. Furthermore, the main gaps in knowledge of badland responses to rainfall and their impacts under current and global change scenarios are identified.

In recent years, soil inoculation with cyanobacteria has become one of the most promising biotechnological strategies for restoring soil functionality in degraded drylands because of their critical role in increasing soil fertility and preventing erosion. Nevertheless, in order to fully exploit this biotechnology on a large scale, it must still be shown whether inoculated cyanobacteria are capable of developing in soils with different physicochemical properties, and new candidates adapted to desert conditions must be explored. To evaluate the potential of cyanobacteria for restoring soil functions of degraded dryland soils, in this laboratory study, we analyzed the effect of inoculating three native N-fixing species (Nostoc commune, Scytonema hyalinum, and Tolypothrix distorta), individually and as a consortium, on soil properties from three different semiarid ecosystems in southeast Spain. The biocrust colonization was monitored by determining chlorophyll a content (the typical surrogate used for biocrust biomass). Other methodologies, such as the analysis of soil spectral response and image classification were also applied for cover estimation of the biocrust. After 3 months, all inoculated soils showed cyanobacteria cover of up to 50%, lower albedo and higher chlorophyll a content. Cyanobacterial inoculation also improved soil functions, as they promoted a significant gain in total organic carbon and total nitrogen in all soils. Among inoculation treatments, Nostoc commune and the mixture of all three species promoted the most cyanobacteria coverage, chlorophyll content, and surface darkening, as well as organic carbon and total nitrogen gains in the soil, highlighting their excellent performance in biocrust development.

Land degradation by erosion is especially important in drylands, which are among the most vulnerable to disturbance by human activity or climate change. Biocrusts are an essential surface component of these ecosystems and one of the most important contributors to surface resistance and stability, and therefore, keeping soil fertile in these nutrient-limited-environments. Loss of biocrusts can result in increased sediment losses and subsequent loss of soil organic carbon (SOC) and other soil resources, which are vital for vegetation and general ecosystem functioning. Despite their importance, the consequences of biocrust loss on sediment and SOC losses in drylands have been poorly analysed. In this study, we examined the influence of two biocrust types (cyanobacteria and lichen-dominated biocrusts) and biocrust removal on runoff and sediment yield, from natural rainfall during one hydrological year in a semiarid badlands catchment (Tabernas, SE Spain). The influence of biocrust type and biocrust removal on SOC losses from water erosion (dissolved and sediment organic carbon losses, DOC and SdOC, respectively) was also analysed. Our results show that sediment yield significantly increased after biocrust removal, especially during the first rain after biocrust removal, when particles were left directly exposed to raindrop impact and easily washed away by runoff. Annual sediment yield was 465, 75 and 24 g m− 2 in biocrust-removed, cyanobacteria-covered and lichen-covered soil, respectively, and the first event represented 87% of annual sediment losses on biocrust-removed plots. Biocrust removal was accompanied by a significant increase in both DOC and SdOC mobilisation. Total organic carbon (TOC) mobilisation was the highest in soils where the biocrust had been removed and decreased as the biocrust was more developed. Annual TOC mobilisation was 10.2, 3.0 and 1.4 g m− 2 in biocrust-removed, cyanobacteria-covered and lichen-covered soil, respectively. TOC mobilisation wa

No-till management and the establishment of plant cover have been implemented in olive crops in recent years in order to prevent soil erosion and increase soil organic carbon. However, the effect of these conservation practices on the net CO2 exchange at the ecosystem scale has not been explored so far. In this study, we analyze the influence of resident vegetation cover (hereafter weeds) on the net ecosystem CO2 exchange (NEE) in an irrigated olive orchard located in Jaén (SE Spain) by using the eddy covariance technique. NEE was measured in the olive orchard under two treatments, one with weed cover in the alleys from autumn to spring, and another where weed growth was avoided by the application of a glyphosate herbicide. Our study demonstrates that the presence of weeds in the alleys increased carbon assimilation in the weed-cover treatment during the weed growing period (from December to April). However, the net ecosystem CO2 uptake decreased in the weed-cover treatment during late spring (May and June), after weeds were cut and left on the soil, compared to the weed-free treatment, probably due to an increase in soil respiration. On an annual basis, weed removal decreased net carbon uptake by 50% compared to the weed-cover treatment. The annual NEE was −140 g C m−2 y−1 in the weed-cover treatment and −70 g C m−2 y−1 in the weed-free treatment. In summary, our study demonstrates that, during the first year of differential treatment, maintenance of weed cover in olive groves has a positive effect on CO2 uptake and enhances the capacity of the agro-system to act as a net CO2 sink.

Terrestrial laser scanning (TLS), widely known as light detection and ranging (LiDAR) technology, is increasingly used to provide highly detailed digital terrain models (DTM) with millimetric precision and accuracy. In order to generate a DTM, TLS data has to be filtered from undesired spurious objects, such as vegetation, artificial structures, etc., Early filtering techniques, successfully applied to airborne laser scanning (ALS), fail when applied to TLS data, as they heavily smooth the terrain surface and do not retain their real morphology. In this article, we present a new methodology for filtering TLS data based on the geometric and radiometric properties of the scanned surfaces. This methodology was built on previous morphological filters that select the minimum point height within a sliding window as the real surface. However, contrary to those methods, which use a fixed window size, the new methodology operates under different spatial scales represented by different window sizes, and can be adapted to different types and sizes of plants. This methodology has been applied to two study areas of differing vegetation type and density. The accuracy of the final DTMs was improved by ~30% under dense canopy plants and over ~40% on the open spaces between plants, where other methodologies drastically underestimated the real surface heights. This resulted in more accurate representation of the soil surface and microtopography than up-to-date techniques, eventually having strong implications in hydrological and geomorphological studies.

Biocrusts play crucial roles in hydrological processes by controlling soil water availability and regulating water redistribution from source to sink areas. Most studies have examined the influence of biocrusts on isolated components of the soil water balance, but few have addressed this matter from an integrated point of view, involving their influence on all components together. Such integration is crucial to elucidate the overall effects of biocrusts on the soil water balance. The aim of this study was to review the role of biocrusts in the soil water balance, by examining their influence on infiltration, evaporation and soil moisture at plot scale, in two contrasting ecosystems of SE Spain. Our results show that biocrust infiltration was higher in flat soils with sandy loam texture than in steep soils with silty loam texture. The influence of biocrusts on infiltration depended on rainfall intensity. Biocrusts increased infiltration with respect to biocrust-removed soils during low intensity rainfalls but showed similar or even lower infiltration than biocrust-removed soils during high-intensity events. As a result of the increase in infiltration and a decrease in evaporation during wet cold periods, biocrusts increased soil moisture when compared with biocrust-removed soils. However, during warm periods, biocrusts and biocrust-removed soils lost water very quickly, thus resulting in similar water losses and moisture content under both types of surfaces. We conclude that biocrusts increase water input by increasing infiltration and soil moisture, and reduce water output by reducing soil evaporation, thus eventually enhancing the available water to plants.

Soil sealing and crusting are common, widespread processes in arid and semiarid soils that strongly affect runoff and erosion. In these soils, biological soil crusts (BSCs) are an essential surface component known to have an important role in water processes, and are also strong erosion protection agents. However, these crusts are also highly vulnerable to disturbances, which seriously affect their pedological and ecological roles. The aims of this study were to examine whether penetration resistance (PR) depends on BSC developmental stage and how removal of BSCs affects PR, under dry and wet soil conditions, and to analyse the relationship between PR and runoff and soil detachment in these soils. This research was conducted in two semiarid ecosystems representative of crusting processes in SE Spain (El Cautivo and Las Amoladeras, Almeria province). Four pairs of plots containing the main BSC types identified at both sites were selected and two treatments were considered, one in each plot in the pair: i) unaltered BSC and ii) BSC removal by scraping. Two intense rainfall simulation experiments were performed one after another in these plots. Runoff was measured during both, and water samples were collected for further determination of sediment yield. PR was measured in undisturbed BSC and scalped soil on dry soil prior to rainfall, on wet soil after the first and second rainfalls, and on dry soil seven months after BSC removal. Crust PR was higher at Las Amoladeras (3.13 ± 0.54 kg cm− 2) than at El Cautivo (1.52 ± 0.74 kg cm− 2) due to soil compaction from trampling by livestock in the former. PR varied with BSC development, with less developed cyanobacteria BSCs showing higher resistance (under dry and wet conditions) than more developed lichen BSCs. BSC removal was followed by the formation of a new seal (physical crust) upon raining, which however, did not result in increased PR. No significant relationship was found between PR and runoff, but there was a weak ne

In arid and semiarid ecosystems, plant interspaces are frequently covered by communities of cyanobacteria, algae, lichens and mosses, known as biocrusts. These crusts often act as runoff sources and are involved in soil stabilization and fertility, as they prevent erosion by water and wind, fix atmospheric C and N and contribute large amounts of C to soil. Their contribution to the C balance as photosynthetically active surfaces in arid and semiarid regions is receiving growing attention. However, very few studies have explicitly evaluated their contribution to organic carbon (OC) lost from runoff and erosion, which is necessary to ascertain the role of biocrusts in the ecosystem C balance. Furthermore, biocrusts are not resilient to physical disturbances, which generally cause the loss of the biocrust and thus, an increase in runoff and erosion, dust emissions, and sediment and nutrient losses. The aim of this study was to find out the influence of biocrusts and their removal on dissolved and sediment organic carbon losses. One-hour extreme rainfall simulations (50 mm h-1) were performed on small plots set up on physical soil crusts and three types of biocrusts, representing a development gradient, and also on plots where these crusts were removed from. Runoff and erosion rates, dissolved organic carbon (DOC) and organic carbon bonded to sediments (SdOC) were measured during the simulated rain. Our results showed different SdOC and DOC for the different biocrusts and also that the presence of biocrusts substantially decreased total organic carbon (TOC) (average 1.80±1.86 g m-2) compared to physical soil crusts (7.83±3.27 g m-2). Within biocrusts, TOC losses decreased as biocrusts developed, and erosion rates were lower. Thus, erosion drove TOC losses while no significant direct relationships were found between TOC losses and runoff. In both physical crusts and biocrusts, DOC and SdOC concentrations were higher during the first minutes after runoff began and decreas

This article presents an overview on the formation and development of this suburb, emphasizing on its most relevant features, especially from the archaeological point of view., En el presente artículo se pretende hacer un recorrido por la génesis y desarrollo del arrabal, poniendo el acento en alguno de sus rasgos más distintivos, tal y como se vienen definiendo desde la arqueología, fundamentalmente.

The interplant soil surfaces in most arid and semiarid ecosystems are covered by biological soil crusts (BSCs). These crusts regulate water inputs and losses through soils and play major roles in local hydrological regimes. In recent years, the role of BSCs in infiltration and runoff has gained increasing importance and better knowledge of their effects on these processes has been acquired. However, the role of BSCs in other important components of the water balance, such as evaporation or soil moisture has hardly been studied, so their effects on these processes remain unknown. The aim of this study was to explore the influence of BSCs on soil moisture regimes in the top layer of the soil in two semiarid ecosystems in SE Spain with different particle-size distributions. At both study sites, soil moisture was monitored at 0.03 and 0.10. m under two types of BSCs, a cyanobacteria-dominated BSC and a lichen-dominated BSC, and in adjacent soils where they had been removed. Our results showed that during wet soil periods, removal of BSCs led to decreased soil moisture, especially in the upper layer (0.03. m), compared to soils covered by BSCs. Decrease in soil moisture was more noticeable after removal of lichens than cyanobacterial BSCs, and more so in fine than in coarse-textured soils. Soil water loss was also generally faster in soils with no BSCs than in soils covered by them. However, no difference was found in soil moisture under either crusted or scalped soils during soil drying periods. The type of BSC influenced soil moisture differently depending on soil water content. During wet soil periods, soil water loss was faster and soil moisture lower under cyanobacterial than under lichen BSCs. On the contrary, during soil drying periods, soils covered by lichens lost water faster and showed lower moisture than those covered by cyanobacteria. Our results show the major role of the presence of BSCs, as well as the types, in soil water content in semiarid ecosystems.

Evaporation of soil moisture is one of the most important processes affecting water availability in semiarid ecosystems. Biological soil crusts, which are widely distributed ground cover in these ecosystems, play a recognized role on water processes. Where they roughen surfaces, water residence time and thus infiltration can be greatly enhanced, whereas their ability to clog soil pores or cap the soil surface when wetted can greatly decrease infiltration rate, thus affecting evaporative losses. In this work, we compared evaporation in soils covered by physical crusts, biological crusts in different developmental stages and in the soils underlying the different biological crust types. Our results show that during the time of the highest evaporation (Day 1), there was no difference among any of the crust types or the soils underlying them. On Day 2, when soil moisture was moderately low (11%), evaporation was slightly higher in well-developed biological soil crusts than in physical or poorly developed biological soil crusts. However, crust removal did not cause significant changes in evaporation compared with the respective soil crust type. These results suggest that the small differences we observed in evaporation among crust types could be caused by differences in the properties of the soil underneath the biological crusts. At low soil moisture (<6%), there was no difference in evaporation among crust types or the underlying soils. Water loss for the complete evaporative cycle (from saturation to dry soil) was similar in both crusted and scraped soils. Therefore, we conclude that for the specific crust and soil types tested, the presence or the type of biological soil crust did not greatly modify evaporation with respect to physical crusts or scraped soils.

Soil surface roughness has a strong influence on runoff and erosion, affecting surface storage capacity, water flow routing and velocity, and modifying runoff rates. It also reduces soil detachment by raindrops and the shear effect of water flow on the soil surface. In arid and semiarid ecosystems, biological soil crusts (BSCs) commonly appear in clearings between plants. Depending on the dominant component in the BSC community, the roughness of the soil surface may vary considerably, changing the hydrologic and erosive response of the soil. The aim of this study is to determine the effect of physical and biological crusts on soil surface roughness and their influence on runoff and erosion. For this purpose, we set up open plots containing different BSC types and treatments and recorded runoff and total erosion from all the events for 18 months. Micro-topographic indexes were calculated from high-resolution digital surface models of the plots built from terrestrial laser scanner height data. After comparing different spatial resolutions and indexes, we concluded that only the local Random Roughness index in a 40-mm moving window provided a precise estimation of the roughness induced by BSCs, though it did not have a direct effect on runoff response. The best relationship between microtopography and runoff on biologically crusted soils was found for surface storage capacity, which appears as a powerful predictor of the runoff coefficient on long temporal scales. Sediment yield was not well predicted by any of the micro-topographic indexes studied. The only index that was significantly related to sediment yield was the local Random Roughness in a 40 mm moving window, but even this explained only a third of the erosion variance.

Soil crusts influence many soil parameters that affect how water moves into and through the soil, and therefore, critically influence water availability, erosion processes, nutrient fluxes, and vegetation distribution patterns in semiarid ecosystems. Soil crusts are quite sensitive to disturbance, and their alteration can lead to modification of the local hydrological regime, thus affecting general functioning of the ecosystem. The aim of this study was to analyze the influence of different types of soil crusts, physical, and biological in different developmental stages, as well as the impact of their disturbance, on infiltration. This was assessed by means of rainfall simulations conducted in two semiarid ecosystems in southeast Spain characterized by different lithologies, topographies, and soil crust distributions. Two consecutive rainfall simulation experiments (50 mm h−1 rainfall intensity), the first on dry soil and the second on wet soil, were carried out in microplots (0.25 m2) containing the most representative soil crust types at each site, each crust type subjected to three disturbance treatments: (a) undisturbed, (b) trampling, and (c) removal. Infiltration in the crusts was higher on coarse- than on fine-textured soils and almost two times greater on dry than on wet soil. Biological soil crusts (BSC) showed higher infiltration rates than physical soil crusts (PSC). Within BSC, infiltration increased as cyanobacterial biomass increased and was the highest in moss crusts. However, late-successional crustose and squamulose lichen crusts showed very low infiltration rates. Trampling reduced infiltration rates, especially when soil was wet, whereas crust removal enhanced infiltration. But this increase in infiltration after removing the crust decreased over time as the soil sealed again due to raindrop impact, making runoff rates in the scraped microplots approach those registered in the respective undisturbed crust types. Our results demonstrate that water

Runoff in arid and semiarid areas is characterized by high spatial and temporal variability. The spatial component is largely associated with the high spatial heterogeneity of soil surface attributes, such as vegetation and rock fragment covers, topography, and soil crust typology. Biological soil crusts (BSCs) are a common soil cover in arid and semiarid areas, and they play an essential role in local hydrological processes, since they affect many soil surface attributes associated with hydrologic properties. Although several publications have reported on the influence of BSCs on runoff at microplot spatial scales, only a few have examined their influence on larger spatial scales. Moreover, very few studies have analyzed the effect of BSCs on runoff under natural rain conditions. This is difficult, since a complex pattern of interactions among rainfall properties, BSC characteristics and some local characteristics, such as topography or type of soil is expected. In addition, in order to achieve a realistic model of how BSCs and rainfall affect runoff, it would be necessary to consider the level of human-driven degradation of BSCs. In this study, runoff was analyzed in plots with varying cover of cyanobacterial and lichen BSCs at microplot and small hillslope scales for two hydrological years in badlands in SE Spain. Structural equation modelling (SEM) was applied to test both direct and indirect relationships of BSC cover, slope gradient, rainfall characteristics and runoff. Our model showed that rainfall characteristics were the main factors controlling runoff yield. The slope positively affected runoff at small hillslope scales, but did not influence runoff at microplot scales. Runoff decreased at both scales with increased lichen-BSC cover. However, this effect was only significant during low-intensity events. Under high rainfall intensities, neither the BSC cover nor the slope had a causal effect on runoff. Our results suggest that incorporation of BSC-crusted

Water and nutrients are scarce resources in arid and semiarid ecosystems. In these regions, biological soil crusts (BSCs) occupy a large part of the soil surface in the open spaces surrounding patches of vegetation. BSCs affect physicochemical soil properties, such as aggregate stability, water retention, organic carbon (OC) and nitrogen (N) content, associated with primary ecosystem processes like water availability and soil fertility. However, the way BSCs modify soil surface and subsurface properties greatly depends on the type of BSC. We hypothesised that physicochemical properties of soil crusts and of their underlying soils would improve with crust development stage. Physicochemical properties of various types of soil crusts (physical crusts and several BSC development stages) and of the underlying soil (soil layers 0–1 cm and 1–5 cm underneath the crusts) in two semiarid areas in SE Spain were analysed. The properties that differed significantly depending on crust development stage were aggregate stability, water content (WC) (at −33 kPa and −1500 kPa), OC and N content. Aggregate stability was higher under well-developed BSCs (cyanobacterial, lichen and moss crusts) than under physical crusts or incipient BSCs. WC, OC and N content significantly increased in the crust and its underlying soil with crust development, especially in the first centimetre of soil underneath the crust. Our results highlight the significant role of BSCs in water availability, soil stability and soil fertility in semiarid areas.

Biological soil crusts (BSCs) are increasingly recognized as common features in arid and semiarid ecosystems and play an important role in the hydrological and ecological functioning of these ecosystems. However, BSCs are very vulnerable to, in particular, human disturbance. This results in a complex spatial pattern of BSCs in various stages of development. Such patterns, to a large extent, determine runoff and erosion processes in arid and semiarid ecosystems. In recent years, visible and near infrared (Vis-NIR) diffuse reflectance spectroscopy has been used for large-scale mapping of the distribution of BSCs. Our goals were (i) to demonstrate the efficiency of Vis-NIR spectroscopy in discriminating vegetation, physical soil crusts, various developmental stages of BSCs, and various types of disturbance on BSCs and (ii) to develop a classification system for these types of ground cover based on Vis-NIR spectroscopy. Spectral measurements were taken of vegetation, physical crusts and various types of BSCs prior to, and following, trampling or removal with a scraper in two semiarid areas in SE Spain. The main spectral differences were: (i) absorption by water at about 1450 nm, more intense in the spectra of vegetation than in those of physical crusts or BSCs, (ii) absorption features at about 500 and 680 nm for the BSCs, which were absent or very weak for physical crusts, (iii) a shallower slope between about 750 and 980 nm for physical crusts and early-successional BSCs than for later-successional BSCs and (iv) a steeper slope between about 680 and 750 nm for the most developed BSCs. A partial least squares regression-linear discriminant analysis of the spectral data resulted in a reliable classification (Kappa coefficients over 0.90) of the various types of ground cover and types of BSC disturbance. The distinctive spectral features of vegetation, physical crusts and the various developmental stages of BSCs were used to develop a classification system. This will be

[ES] Las costras físicas (CFS) y biológicas (CBS) del suelo ocupan una gran extensión en zonas áridas y semiáridas de todo el mundo. En estos medios, el encostramiento del suelo tiene una gran influencia sobre los procesos hidrológicos y erosivos. Los objetivos que se persiguen en este trabajo son: analizar las características de las costras que influyen en la infiltración y en la erosión e identificar cuáles de estas características tiene una mayor influencia sobre estos procesos. En dos áreas semiáridas representativas en la provincia de Almería se identificaron los principales tipos de costras físicas y biológicas. Para cada tipo de costra, se analizaron las características físicas y químicas de la propia costra y del material subyacente, así como su rugosidad, hidrofobia, resistencia a la penetración y cobertura de diferentes comunidades de organismos. Para analizar la influencia de las costras sobre la infiltración y la erosión, se llevaron a cabo simulaciones de lluvia en parcelas con la costra intacta y para examinar los efectos de las características del material subyacente a la costra, los experimentos de simulación de lluvia se realizaron tras retirar la costra. La respuesta hidrológica de las áreas encostradas estudiadas se ve afectada no solo por las características de la costra, sino también por las características del suelo sobre el que se desarrollan estas costras y especialmente por la pendiente que aparece como una variable altamente predictiva para la infiltración y la erosión. Entre las características del material subyacente, resalta la influencia de la textura, el contenido en carbono orgánico y la conductividad eléctrica, y entre las características de la costra, la cobertura y rugosidad son las variables más predictivas que explican las diferencias en las tasas de infiltración y erosión entre ambos sitios., [EN] Physical soil crusts and biological soil crusts occupy a wide extension in arid and semiarid areas all over the world. In these regions, soil crusting has a very strong influence on local hydrologic regimes and erosion. The main purposes of this paper are: 1) to examine how crust characteristics influence infiltration and erosion and 2) to identify the most influential crust characteristics on runoff and erosion processes. Two semiarid areas in the province of Almería were chosen and the most representative physical and biological soil crusts were identified at both sites. For each crust type, physical and chemical characteristics of the crust and the soil underneath the crust were analysed, as well as other crust properties like roughness, hydrophobicity, resistance to penetration and cover. To analyse the influence of the crust on infiltration and erosion, rainfall simulations were conducted on plots with the intact crust, and in order to examine the influence of the soil underlying the crust, rainfall simulations were conducted on plots after removing the crust. The hydrological response of the studied encrusted areas is affected, not only by the characteristics of the crust itself, but also by the characteristics of the soil in where the crust is developed and specially by the slope gradient that appears like a highly predictive variable for infiltration and erosion. Among the properties of the soil material below crusts, it is remarkable the influence of soil texture, organic carbon content and electrical conductivity, and among the properties of the crust, cover and roughness are the most predictive variables explaining the differences in infiltration and erosion between sites.

The spatial variability of soil aggregate stability and its relationship to runoff and soil erosion were examined in a catena of soils and vegetation in a semiarid environment at the Rambla Honda field site (Tabernas, Almería, SE Spain) to evaluate the validity of structural stability as a soil erosion indicator in sandy loam range soils. The influence of soil properties and topography on the variability of aggregate stability was also examined. Methods include: 1) aggregate stability assessment at 12 sites (3 repetitions per site) on the hillslope by two methods: a) aggregate size distribution by dry sieving b) water drop test; 2) soil organic carbon content; 3) particle size distribution determination; 4) terrain attributes derived from a digital elevation model (1-m resolution); 5) monitoring runoff and erosion for nearly 3 years in eight (10 × 2 m) plots distributed over the hillslope. Results: 41% of the average soil mass is formed by > 2-mm aggregates. However, wet aggregate stability is poor, with a mean (of a total of 1440 aggregates) of only 26 drop impacts necessary to break up a wet aggregate (pF = 1). Significant relationships were found in the number of water drops required for aggregate breakdown and runoff and erosion rates. However, no significant relationships between the mean weight diameter of aggregates under dry conditions and runoff or erosion rates were observed. The relationships of aggregates with other soil properties, hillslope position and proximity to plants are also analysed. The most significant correlation found was between the number of drop impacts and soil organic matter content. The stability of topsoil aggregates seems to be a valuable indicator of field-assessed runoff and inter-rill erosion of sandy loam range soils under semiarid conditions. © 2008 Elsevier B.V. All rights reserved.