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The structural stability of soil is a physical characteristic that affects soil degradation processes. Calcium‐based amendments, such as calcium carbonate, calcium sulfate, and calcium oxide/hydroxide, have been shown to improve the stability of soil aggregates. This study seeks to determine which calcium‐based soil amendments, and at what concentration, are the most efficient in improving aggregate stability of sandy topsoils derived from granitic and metamorphic parent materials, and to analyze the mechanisms involved. In the pot experiment, soils amended with CaCO3, CaCl2, and CaSO4 did not present significant differences in aggregate stability compared to the control or among each other. In contrast, Ca(OH)2 soil amendment brought the greatest stability to the soil aggregates. A dose of 1% Ca(OH)2 significantly increased the stability of soil aggregates. This effect is due to the reaction of Ca(OH)2 with atmospheric CO2 which leads to the formation of CaCO3, a delayed reaction not showed by the other soil amendments tested. Likewise, the greater solubility of Ca(OH)2 compared to CaCO3 exerts a greater aggregation effect on soil. Thus, the mechanism of action of Ca(OH)2 is related to cementation, rather than flocculation. Future studies should be carried out to demonstrate the effectiveness of Ca(OH)2 under field conditions. [ABSTRACT FROM AUTHOR]

Abstract: Using concepts of connectivity in challenges regarding land and water management (flooding, erosion, nutrient leaching, landslides) can only be fully harnessed if knowledge is communicated well between scientists and stakeholders. Proper communication requires prior understanding of end‐users' perception of connectivity as a useful framework. Therefore, we analysed (a) perceptions of ‘connectivity’ for stakeholders involved in water and land management across Europe, (b) potential for stakeholders to apply connectivity‐related measures in their management decisions, (c) stakeholders' biggest challenges in water and land management, and (d) stakeholders' expectations for future connectivity research agendas. We studied 85 questionnaires from 19 countries using a grounded theory approach. One third of stakeholders understood connectivity in its scientific context, whereas 39% perceived connectivity indirectly through their personal experiences (e.g., water and sediment fluxes and erosion). Half of stakeholders' perceived links and challenges were related to availability of data and methods, communication, and institutions or policy, whereas others believed they were related to water quality and quantity, soil erosion and quality, and climate change. Half of the stakeholders considered connectivity management important, and one third showed high interest in managing connectivity. Adopting connectivity into management is hindered by institutional‐ and policy‐based management limitations, insufficient data and methods, and ineffective knowledge transfer. Explicitly considering heterogeneity of stakeholder perceptions is required for projects regarding management of connectivity at European, national, and local scales. [ABSTRACT FROM AUTHOR]

Abstract: Soil resources are important for the socioeconomic development of the Mediterranean area. Their durability may be threatened because of intense erosion processes that result in severe degradation in the field (on‐site effects) and downstream degradation (off‐site effects). Based on the literature and results obtained during several research projects, this paper presents the main lessons and challenges dealing with Mediterranean soil resources under global change. After a review of the main drivers of Mediterranean soil erosion and the main impacts of water erosion processes, the paper highlights that the nature and intensity of active erosion processes are as diverse as the mosaic of the Mediterranean landscape. It then discusses the expected evolution of Mediterranean soil resources under global change and illustrates the prevalent influences of land use (partly depending on climatic constraints) on the evolution of erosion risk and soil vulnerability. Finally, it details some main challenges for the future of Mediterranean soil resources dealing with a better knowledge of factors and processes involved in soil erosion, a better evaluation of soil vulnerability through a combined quantitative and qualitative soil erosion approach, and the need for a site‐specific conservation strategy for Mediterranean soil resources. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Shrink-swell soils, such as those in a Mediterranean climate regime, can cause changes in terms of hydrological and erosive responses because of the changing soil water storage conditions. Only a limited number of long-term studies have focused on the impacts on both hydrological and erosive responses and their interactions in an agricultural environment. In this context, this study aims to document the dynamics of cracks, runoff and soil erosion within a small Mediterranean cultivated catchment and to quantify the influence of crack processes on the water and sediment supplied to a reservoir located at the catchment outlet using water and sediment measurements at a cultivated field outlet as baseline. Detailed monitoring of the presence of topsoil cracks was conducted within the Kamech catchment (ORE OMERE, Tunisia), and runoff and suspended sediment loads were continuously measured over a long period of time (2005-2012) at the outlets of a field (1.32 ha) and a catchment (263 ha). Analysis of the data showed that topsoil cracks were open approximately half of the year and that the rainfall regime and water table level conditions locally control the seasonal cracking dynamics. Topsoil cracks appeared to seriously affect the generation of runoff and sediment concentrations and, consequently, sediment yields, with similar dynamics observed at the field and catchment outlets. A similar time lag in the seasonality between water and sediment delivery was observed at these two scales: although the runoff rates were globally low during the presence of topsoil cracks, most sediment transport occurred during this period associated with very high sediment concentrations. This study underlines the importance of a good prediction of runoff during the presence of cracks for reservoir siltation considerations. In this context, the prediction of cracking effects on runoff and soil erosion is a key factor for the development of effective soil and water management strategies and downstream reservoir preservation. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Reservoir siltation because of water erosion is an important environmental issue in Mediterranean countries where storage of clear surface water is crucial for their economic and agricultural development. The high density of gully systems observed in Mediterranean regions raises the question of their contribution to reservoir siltation. In this context, this study quantified the absolute and relative contributions of rill/interrill and gully/channel erosion in sediment accumulation at the outlet of small Tunisian catchments (0·1-10 km2) during the last 15 years (1995-2010). To this end, a fingerprinting method based on measurements of caesium-137 and total organic carbon combined with long-term field monitoring of catchment sediment yield was applied to five catchments in order to cover the diversity of environmental conditions found along the Tunisian Ridge and in the Cape Bon region. Results showed the very large variability of erosion processes among the selected catchments, with rill/interrill erosion contributions to sediment accumulated in outlet reservoirs ranging from 20 to 80%. Overall, rill/interrill erosion was the dominant process controlling reservoir siltation in three catchments whereas gully/channel erosion dominated in the other two catchments. We identified the presence of marly gypsum substrates and the proportion of catchment surface covered by soil management/conservation measures as the main drivers of erosion process variability at the catchment scale. These results provided a sound basis to propose guidelines for erosion mitigation in these Mediterranean environments and suggested to apply models simulating both rill/interrill and gully/channel erosion in catchments of the region. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Aggregate stability is a key property affecting the movement and storage of water, seedling emergence, and soil sensitivity to erosion. Many studies have shown that aggregate stability changes through time. Field monitoring studies performed with a relatively large (monthly) time step showed the seasonal trend of aggregate stability. However, shorter time step monitoring is required to explore dynamics of aggregate stability at short term. For now, biological activity was recognized to be the main factor of aggregate stability dynamics, but previous studies were currently based on the external stimulation of aggregate stability. The objectives of this study were to assess variations in aggregate stability at short time steps in the field and to identify the factors controlling these variations of stability. A 6-mo field monitoring was performed at short time step (2-5 d) on a bare field of Luvisol without organic amendment. Aggregate stability was measured for both on surface and subsurface materials by the ISO 10930 (2012) method. Rain amount and intensity, air temperature and humidity, soil temperature, water content and hydric history, and soil water repellency were measured as explanatory factors. The results showed that aggregate stability varied greatly (up to 40%) over a few days for both surface and subsurface. Short term dynamics of aggregate stability were already shown by laboratory experiments, but such dynamics was never observed in the field for a bare soil without external stimulation of biological activity. For the surface, short time step variations of surface aggregate stability were primarily controlled by soil water content (WC0 and WC1/2), hydric history (ΔWC4 and API), and rain intensity. While large changes in aggregate stability were found for the subsurface, explanatory factors remain to be found. [ABSTRACT FROM AUTHOR]

The sedimentological connectivity of agricultural catchments may be affected by anthropogenic structures (land management practices) established to reduce sediment exportation from agricultural plots to water streams. Distributed erosion models may in theory provide information about where and how these structures should be installed in catchments to reduce sediment exportation. The interaction between sediment exportation and land management practices is very complex from both theoretical and experimental points of view. Vegetated filters are a widely used land management practice. They interact with water flow, change turbulence conditions, and ultimately affect sediment transport and deposition processes. Experimental results have shown that the efficiency of sediment trapping in vegetated filters is influenced by flow characteristics, sediment size, and vegetation type, as well as by the slope and width of the filter in the streamwise direction. At the catchment scale, the spatial organisation of management practices is crucial for the global sedimentological connectivity. Present-day erosion models propose different approaches to simulate the influence of management practices on soil loss and sediment export for agricultural catchments. Some of them use the Sediment Delivery Ratio (SDR) or P-factor to describe sediment transport from source to sink areas. Others, such as in the TRAVA and VSFMOD, rely on process-based descriptions involving changes in roughness and infiltrability along flow paths to study the effect of management practices. From the literature review conducted herein, we identified the lack of an approach of intermediate complexity, that would be more physically relevant than SDR and P-factor approaches, but simpler and easier to spatialise than TRAVA and VSFMOD-type models. Copyright © 2010 John Wiley and Sons, Ltd. [ABSTRACT FROM AUTHOR]

Splash is an essential process in interrill erosion because it detaches soil fragments front their substrate and transports them. However, splash measurements are difficult to interpret and relatively little is known about the influence of particle characteristics on the spatial distribution of splash. The objective of this work is to study the splash distribution of different size fractions for aggregated soils. We used a recently proposed theory for spatial distribution by splash to interpret experimental data on the radial distribution of soil fragments splashed by simulated rainfall. A laboratory device with five concentric rings was used to determine average splash lengths for 16 fragment size fractions (0.05 to >2000 μm) of rout soils. Sieved soil (3- to 5-mm size fraction) was exposed to simulated rainfall at 29 mm h-1 and with a time-specific kinetic energy of 252 J m-2 h-1. We interpreted the measured masses of fragments splashed into the different rings using an approximate solution of the exponential splash distribution theory applied to the experimental design. We demonstrated that the theory is valid for hulk aggregated soil as well as for individual fragment size fractions. The derived average splash lengths ranged from 4 to 23 cm, depending on the fragment size and soil. Splash lengths were greatest for soil fragments of 100 to 200 μm, and decreased for finer and coarser size fractions. Comparison of these findings with physically-based theory suggests that the coarser fragments, 50 to 2000 μm, are transported as single airborne particles, whereas the smaller ones. <50 μm, are transported in groups in splash droplets. This interpretation is consistent with observations reported in the literature. [ABSTRACT FROM AUTHOR]

Various interactions, particularly those existing between the rainfall intensity, the slope gradient, the slope length, and the tillage supposedly can affect the runoff features for interrill erosion. Despite numerous studies, their effect on runoff production and pathways and the resulting soil losses have seldom been analyzed. This is especially true under field and tillage conditions. This study investigated the effect of rainfall intensity, slope length, and gradient on runoff amount and pathways for interrill erosion in tilled fields. Runoff features and soil losses were evaluated on bounded plots of 1- and 5-m length located on 4 to 8% slope gradients, and under natural and simulated rainfalls with intensities ranging from 1.5 to 30 mm h[sup -1]. Runoff coefficients (R) ranged from 34 to 98% whereas sediment concentrations (SC) varied from 2.9 to 49 g l[sup -1]. The runoff coefficient was affected by all three factors: rainfall intensity (r = 0.48; P < 0.0001), slope gradient (r = 0.51; P < 0.0001) and slope length (r = 0.29; P = 0.02); whereas SC was correlated with only rainfall intensity (r = 0.48; P < 0.0001) and slope length (r = 0.44; P = 0.0004). The runoff coefficient and SC ratios between 1- and 5-m long plots were systematically greater for the intermediate rainfall intensity. Runoff features mainly affected by tillage implements may explain higher interrill erosion at longer and steeper slopes. Lower differences between 1- and 5-m plots at high rainfall intensity may reflect greater ponded runoff absorbing raindrop kinetic energy and lowering detachment and transport processes. Finally, the effects of rainfall intensity, slope length, and gradient and tillage are discussed in respect of possible erosion processes operating in the experiments. [ABSTRACT FROM AUTHOR]

Because soil surface structure has a considerable influence on infiltration rate, the sealing process is postulated to have a significant effect on herbicide loss through runoff. We evaluated the effect of degraded soil surface structures on herbicide loss in runoff, and used the experimental data to test the uniform mixing zone concept and two‐site sorption kinetics for modeling herbicide transfer to runoff. The experiments were done with simulated rainfall on 10‐m2 plots in the field and 0.25‐m2 plots in the laboratory after a surface application of 1.5 kg ha−1 of isoproturon [3‐(4‐isopropylphenyl)‐1,1‐dimethylurea] and 0.187 kg ha−1 of diflufenican [2′,4′‐difluoro‐2‐(α,α,α‐trifluoro‐m‐tolyloxy) nicotinanilide]. Isoproturon (IPU) and diflufenican (DFF) concentrations were very high in the first runoff (up to 60 mg L−1 for IPU and 2 mg L−1 for DFF) when simulated rainfall was applied 24 h after the treatment. The concentrations decreased very rapidly with total rainfall depth. Degradation of the structural state of the soil surface increased the ratio of pesticide loss to application rate from 0.3 to 10% for IPU and from 0.7 to 7.8% for DFF for a runoff depth of less than 1 mm. The structural state of the soil surface influences the rapidity at which runoff begins after the onset of rain, and the runoff coefficient at steady state. Furthermore, the development of a surface seal seems to limit the depth of soil–runoff interaction and thus influences the dynamics of herbicide mobilization. Concentrations of IPU in the runoff were satisfactorily described with a model incorporating a uniform mixing zone and two‐site sorption–desorption. [ABSTRACT FROM AUTHOR]