Search

Abstract: Increased soil erosion, pressure on agricultural land, and climate change highlight the need for new management methods to mitigate soil loss. Management strategies should utilize comparable data sets of long‐term soil erosion monitoring across multiple environments. Adaptive soil erosion management in regions with intense precipitation requires an understanding of inter‐annual variability in sediment yield (SY) at regional scales. Here, a novel approach is proposed for analysing regional SY. We aimed to (i) investigate factors controlling inter‐ and intra‐annual SY, (ii) combine seasonality and time compression analyses to explore SY variability and (iii) discuss management implications for different Mediterranean environments. Continuous SY measurements totalling 104 years for eight small catchments were used to describe SY variability, which ranged from 0 to 271 t/ha/year and 0 to 116 t/ha/month. Maximum SY occurs in spring to summer for catchments with oceanic climates, while semi‐arid or dry summer climates experience SY minimums. We identified three time compression patterns at each time scale. Time compression was most intense for catchments with minimum SY in spring to summer. Low time compression was linked to very high soil loss, low run‐off and sediment production thresholds, and high connectivity. Reforestation, grassland and terracing changed SY magnitudes and time compression, but failed to reduce SY for large storm events. Periods with a high probability of high SY were identified using a combination of intra‐annual SY variability, seasonality analysis, and time compression analysis. Focusing management practices on monthly flow events, which account for the majority of SY, will optimise returns in Mediterranean catchments. [ABSTRACT FROM AUTHOR]

Research gaps in understanding flood changes at the catchment scale caused by changes in forest management, agricultural practices, artificial drainage, and terracing are identified. Potential strategies in addressing these gaps are proposed, such as complex systems approaches to link processes across time scales, long-term experiments on physical-chemical-biological process interactions, and a focus on connectivity and patterns across spatial scales. It is suggested that these strategies will stimulate new research that coherently addresses the issues across hydrology, soil and agricultural sciences, forest engineering, forest ecology, and geomorphology. [ABSTRACT FROM AUTHOR]

Mediterranean catchments are characterized by strong nonlinearities in their hydrological behaviour. Properly simulating those nonlinearities still represents a great challenge and, at the same time, an important issue in order to improve our knowledge of their hydrological behaviour. The main aim of this work is find out diverse modelling approaches to reproduce the observed nonlinear hydrological behaviour in a small Mediterranean catchment, Can Vila (Vallcebre, NE Spain). To this end, three hydrological models were considered: two lumped models called LU3 and LU4 of increasing complexity, and a distributed model called TETIS. The structures of these different models were used as hypotheses, which could explain and reproduce the observed nonlinear behaviour at the outlet. Four analyses were carried out: (i) goodness-of-fit criteria analysis, (ii) residual errors analysis, (iii) sensitivity analysis and (iv) multicriteria analysis based on the concept of Pareto Optimal. These analyses showed the higher capability and robustness of the distributed model to reproduce the observed complex hydrological behaviour in this catchment. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In achieving the final objective of the European Water Framework Directive, the evaluation of the 'hydrological status' of a water body in a catchment is of the utmost importance. It represents the divergence of the actual hydrological regime from its 'natural' condition and may thus provide crucial information about the ecological status of a river. In this paper, a new approach in evaluating the hydrological status of a temporary river was tested. The flow regime of a river has been classified through the analysis of two metrics: the permanence of flow and the predictability of no-flow conditions that were evaluated on monthly streamflow data. This method was applied to the Candelaro river basin (Puglia, Italy) where we had to face the problem of limited data availability. The Soil and Water Assessment Tool model was used when streamflow data were not available, and a geographic information system procedure was applied to estimate potential water abstractions from the river. Four types of rivers were identified whose regimes may exert a control on aquatic life. By using the two metrics as coordinates in a plot, a graphic representation of the regime can be visualized in a point. Hydrological perturbations associated with water abstractions, point discharges and the presence of a reservoir were assessed by comparing the position of the two points representing the regime before and after the impacts. The method is intended to be used with biological metrics in order to define the ecological status of a stream, and it could also be used in planning the 'measures' aimed at fulfilling the Water Framework Directive goals. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT The assessment of the ecological status of water bodies, as requires by the European Water Framework Directive, can raise a number of problems when applied to temporary streams. These problems are because of the particular physical, chemical and biological conditions resulting from the recurrent cessation of flow or even the complete drying of the stream beds. In such non-permanent water bodies, the reference quality standards developed for permanent streams may only be applicable under certain circumstances or may not be applicable at all. Work conducted within the collaborative EU-funded project Mediterranean Intermittent River ManAGEment (MIRAGE) has addressed most of these difficulties and has used diverse approaches to solve them. These approaches have been brought together in the so-called MIRAGE Toolbox. This toolbox consists of a series of methodologies that are designed to be used in a sequential manner to allow the establishment of the ecological and chemical status of temporary streams and to relate these findings to the hydrological status of the streams. The toolbox is intended to serve the following purposes: (i) the determination of the hydrological regime of the stream; (ii) the design of adequate schedules for biological and chemical sampling according to the aquatic state of the stream; (iii) the fulfillment of criteria for designing reference condition stations; (iv) the analysis of hydrological modifications of the stream regime (with the definition of the hydrological status); and (v) the development of new methods to measure the ecological status (including structural and functional methods) and chemical status when the stream's hydrological conditions are far from those in permanent streams. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Knowledge of soil moisture dynamics at reasonable temporal and spatial resolutions is required to improve hydrological understanding and modelling. However, in the Mediterranean area, considered as one of the most vulnerable areas to global change, there is a severe lack of detailed soil moisture data sets. The objective of this study is to investigate the inter-annual and intra-annual spatial and temporal distributions of soil moisture in a Mediterranean mountain area, using the detailed hydrological data set gathered in the Vallcebre Research catchments (NE Spain). With the use of time-domain reflectometry, soil moisture was measured weekly between 1998 and 2003 at eight representative profiles. Time series of soil moisture showed a clear seasonal pattern. Results obtained revealed that soil moisture on hillslopes under forest cover was lower than in downslope areas covered with grasses. However, differences were not persistent through the year but were minimal during the driest and wettest conditions and maximal during the drying and wetting-up periods. During the wetting-up and drying-down periods, the soil moisture distribution depended mainly on local controls. However, during wet conditions, soil moisture patterns were controlled by nonlocal factors that limited the vegetation-related variability of soil moisture. In this mountain area, forest cover is likely to increase as the climate changes, which will most probably reduce the average soil moisture at the catchment scale as well as its spatial variability. These changes may ultimately be seen as a threat to the future of water resources in this area. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article offers a study on the analysis of the relationship among the Scots pine transpiration, meteorological data, and rainfall data in the Vallcebre research catchments in Northeast Iberian Peninsula. It states that the Scots pine transpiration reactions to the rainfall variability, soil water stress, and water table depth variants from 1997-2000 was analyzed. The results show that the rates of Scots pine transpiration are restricted by the availability of soil water.

When a large number of determinations of soil water retention characteristics are required, the choice of the method used for obtaining them must be based on the compromise between the quality of the results and the effort needed for its implementation. We evaluated the use of the pedotransfer functions (PTFs) included in the ROSETTA model and compared them with ones obtained specifically for silt-loam soils. Water retention curves were obtained from unaltered samples by the ‘sand box’ and the pressure membrane methods. At the same time, physical and chemical properties of the samples were determined and then used as input variables for the ROSETTA model and for determining site-specific PTFs (SS-PTFs) by multiple regression. The pedotransfer methods were compared with water retention curves obtained by a simpler sample-averaging method. The uncertainty of each method was evaluated in terms of the mean error (ME) and the root mean square error (RMSE) of the predictions. Effort, in terms of time consumed by field sampling and laboratory determinations for the application to 100 samples, was calculated. The results indicated that the efficiencies of the methods are similar to those obtained by other authors, but we found with homogeneous soils that the ratios between quality of results and effort favour the simpler approaches. Incertitude et efficience des fouctious de pédotransfer pour l′estimation des propriétés de rétention hydrique des sols. Résumé Quand un grand nombre de déterminations des caractéristiques de rétention d’eau des sols sont nécessaires, le choix de la méthode utilisée pour leur obtention doit être basé sur un compromis entre la qualité des résultats et l’effort réalisé pour son implémentation. Nous avons vérifié l’utilisation des fonctions de pédotransfert (PTFs) inclues dans le logiciel ROSETTA et nous les avons comparées avec les fonctions développées spécifiquement pour des sols limoneux fins et limoneux fins argileux. Nous avons obtenu les courbes de rétention de l’eau avec les méthodes du bac à sable et de la membrane de pression. Dans le même temps, les propriétés physiques et chimiques des échantillons ont été analysées et utilisées ensuite comme variables d’entrée pour le modèle ROSETTA et pour la détermination de PTFs spécifiques à l’aide de régressions multiples. Enfin, nous avons comparé les méthodes de pédotransfert avec les courbes de rétention obtenues selon une méthode plus simple utilisant la moyenne d’un petit nombre d’échantillons. L’incertitude de chacune des méthodes a été estimée avec les mesures de l’erreur moyenne (ME) et de la racine carrée de la moyenne des erreurs élevées au carré (RMSE). Nous avons calculé l’effort, mesuré comme le nombre d’heures consommées pour les travaux de terrain et laboratoire, pour un nombre de 100 échantillons. Les résultats nous ont montré que les efficiences de ces méthodes sont semblables à celles obtenues par d’autres auteurs, mais nous avons trouvé que, pour des sols homogènes, la relation entre la qualité des résultats et l’effort favorise les approches les plus simples. [ABSTRACT FROM AUTHOR]

The article discusses a study about the spatial and temporal variability of the hydrological response in a small Mediterranean research catchment, Cal Rodó. The main purpose of the study is to examine the rainfall-runoff relationship in the catchment in an attempt to characterize the non-linearity of its hydrological response. The greater seasonality of the hydrological response of the catchment was manifested at the event scale. The spatial and temporal non-linearities of the rainfall-runoff relationship observed in the catchment and reported in other Mediterranean catchments have direct implications on hydrological modelling.

The Vallcebre research catchments are located in the south-eastern Pyrenees, in an area of diverse land use and varying levels of degradation, including forested hillslopes, abandoned agricultural terraces and badland areas. Outside the badlands, the hydrological response iscontrolled by saturation mechanisms. Between September and June the spatial patterns of saturated areas and soil moisture are determined by subsurface flow, modified by the premature saturation of the inner parts of agricultural terraces, and the negative soil moisture anomalies induced by forest patches overgrown in grassland areas. During summer, this behaviour ceases because of soil moisture depletion and badland surfaces are the only hydrologically active areas, producing excess runoff in response to the intense rainstorms. During the beginning and the ending of the wet season, the saturation of active areasshows a hysteretic behaviour that breaks the linearity between the mean water reserve of the basin and the relative saturated area. [ABSTRACT FROM AUTHOR]

The sediment budget of the small research catchment of Cal Parisa (Vallcebre, Eastern Pyrenees) was studied by hydrological monitoring and assessment of the erosion rates in the major sediment sources. Thisarea is characterized by clayey mudrock prone to landsliding and badland erosion, but the catchment was selected in an area free of majorbadland features, as a representative of middle mountain regions where a system of terraces and drainage ditches had been built for agricultural use but is now abandoned. Streamwater chemistry is dominated by Ca2+ and HCO3- at concentrations close to calcite saturation. Total dissolved solids show dilution during runoff peaks and positive hysteresis loops that support a slow contribution of subsurface water. Relative dissolved ion concentrationsare different for each event analysed. Particulate sediment yield isvery low and represents only about 1 per cent of gross erosion in the catchment. Mineralogical analysis of suspended sediments shows an enrichment in calcite because of precipitation. Chemical analysis of suspended sediments, using common one-litre water samples, shows higher contents of Ca, P and Mn in transported sediment than in sediment source areas, attributed to the precipitation of calcite, and enrichment in organic particulate matter during events respectively for the two first elements, whereas enrichment in Mn remains uncertain. Solid matter yield is therefore clearly dominated by dissolved transport asa result of both high calcium bicarbonate concentrations in runoff waters and strong suspended sediment conveyance discontinuities. Land conservation structures are very effective because they are in good condition whereas the soil is covered by dense permanent vegetation. Nevertheless, this state is unstable because the network of drainage ditches needs maintenance; its spontaneous breakdown after abandonmentmay result in the rearrangement of the elementary stream network andgullyi [ABSTRACT FROM AUTHOR]