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Abstract: Basin management demands a sound understanding of sediment dynamics, particularly in Mediterranean mountain catchments with badlands, which affect water bodies and freshwater ecosystems. Connectivity has emerged as a framework for understanding how sediments move between geomorphic zones. We analyse the feasibility of excess lead‐210 (210Pbex) to study sediment connectivity in a 4‐km2 Mediterranean mountain basin with badlands (Vallcebre research catchments, Eastern Pyrenees) by applying mass‐balance models for hypothesis generation and experimental testing. Badlands in the area are weathered by freezing during the winter and are eroded in summer by high‐intensity showers. The eroded sediments may remain deposited within the streams from months to years. Application of 210Pbex balance models in our basin suggests: (i) a saw‐tooth seasonal pattern of badland surface 210Pbex activities (increasing from October to May, and depleted in summer) and (ii) a downstream increase in sediment activity due to fallout lead‐210 accumulation in stream‐bed sediment deposits. Our experimental results (obtained during 2013 and 2014) showed low sediment 210Pbex concentrations, illustrating the fresh‐rock origin of sediments, but also hampering their study due to high measurement uncertainty (especially for sediments with d50 > 20 μm) and dependence on sampling methods. Suspended sediment 210Pbex activity reproduced the simulated seasonal activity patterns for the badland surfaces. However, sediment activity decreased downstream, suggesting that flushing of fine sediments by flooding prevents fallout lead‐210 accumulation on the stream bed. Overall, high sediment connectivity was revealed between the badlands, streams and outlet of the basin, as well as the fast transmission of 210Pbex by the finest sediment fraction. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Purpose: First flushes can be crucial to sediment transport in fluvial systems of drylands, as temporary streams are a characteristic feature of Mediterranean basins. After a wildfire, storm flows may enhance runoff delivery to channels, so increasing the first-flush effect. Cs and Pb were used as tracers for recognizing the first post-fire flush effect on the source ascription of bed sediments temporarily stored in a Mediterranean temporary stream severely affected by a wildfire. Materials and methods: Thirty sediment source samples were collected along one of the tributaries of a catchment (4.8 km) located in Mallorca during a field campaign some weeks after the wildfire. The sample collection took into account effects of the wildfire and distinguished between soil surface and channel bank. To measure the source contribution temporarily stored with the bed sediment, five sediment samples-deposited during the first storm, occurring 3 months after the wildfire-were collected from the bed of the main channel. The Cs and Pb concentrations were measured by gamma spectrometry. Then, a linear mixing model was used to establish the contribution of each source type to the bed sediments along the main stream. Results and discussion: First post-fire flush effect was generated by a torrential event with a suspended sediment concentration peak of 33,618 mg L, although transmission losses under a very low runoff coefficient (1%) promoted sediment deposition. Significant differences were observed in fallout radionuclide concentrations between burned surface soil and burned channel bank samples ( p < 0.05), as well as between burned and unburned sources in the downstream part of the catchment ( p < 0.01). The radioactivity concentrations in bed sediment samples were statistically similar ( p > 0.05). Source ascription in bed sediments upstream shows that 67% was generated from burned hillslopes, reaching 75% in the downstream part, because downstream propagation of the sediment derived from the burned area. Conclusions: Bed sediments were mostly generated on burned surface soils because of the fire's effect on soil and sediment availability, high-intensity rainfall, and the limited contribution of channel banks, because these are fixed by dry-stone walls. This hydro-sedimentary response indicates an association between these factors driving erosion and sediment delivery, generating effective slope-to-channel sediment connectivity. The integration of the short-term response with the medium- and long-term analysis will allow for the analysis of the evolution of catchment sediment sources in future studies, determining if fire modifies the catchment sensitivity to that specific disturbance. [ABSTRACT FROM AUTHOR]

• Alteration of sediment properties during transport and storage in a temporary stream. • The spatial variability of soil properties was higher than the in-channel variability. • Colour properties showed the highest temporal and spatial stability. • Results are relevant for future sediment fingerprinting studies. Soil properties used as tracers in sediment fingerprinting studies are assumed to remain stable or vary in a predictable way in their transfer from sources to sinks, allowing a comparison with suspended sediment properties. Attention to the conservative behaviour of soil properties has largely focused on the differences in the particle size and organic matter content between sources and target sediments. However, in-channel biochemical alterations are also known to occur, and their magnitude is still poorly understood. An experiment to investigate the in-channel variations of soil properties during transport and storage was carried out with the most common soil properties used as tracers in sediment fingerprinting studies (i.e. colour, fallout radionuclides and geochemical elements). Twenty-eight soil samples collected from different land uses were introduced into an intermittent stream channel of a small Mediterranean catchment. Samples were recovered at different time intervals over one year. The changes in soil properties (average coefficient of variation 8.1 ± 8.8 %) were generally lower than the spatial variability of each source within the catchment (average coefficient of variation 16.3 ± 18.5 %). No significant differences were observed between samples from different land use types or when recovered at different time intervals. Soil properties that showed higher in-channel coefficients of variation were S, 137Cs, 210Pb ex , As, Mo and Na, with annual coefficients of variation > 19 %. Conversely, carbon (C) and colour properties were the most stable in time (average coefficient of variation 2.1 ± 0.4 % and 2.6 ± 2.2 %, respectively). The results presented will be informative with regard to performing future suspended sediment fingerprinting studies in Mediterranean catchments, providing a better understanding of which soil properties are more sensitive to in-channel biochemical alterations. [ABSTRACT FROM AUTHOR]

Soil erosion and sediment transport are controlled by complex factors promoting variable responses in catchment's erosion rates and sediment yields. To mitigate eventual negative effects derived from altered fluxes, integrated catchment management plans should assess the sediment cascade from upstream erosive processes, sediment mobilization through hillslopes and within the channel, up to downstream sediment yields. This study links hydro-sedimentary dynamics with sediment fingerprinting source ascription in a mid-mountainous Mediterranean catchment during five hydrological years (2013–2018). Soil colour parameters and fallout radionuclides were used as tracers to predict dominant suspended sediment sources using (i) a Bayesian mixing model (MixSIAR) and (ii) an End Member Mixing Analysis (EMMA). MixSIAR suggested that crops were the dominant source in most of the collected samples. EMMA showed similar results, clustering all except one sediment samples close to the crop and channel bank signatures. In addition, a quantitative hysteresis index was calculated and floods were clustered in function of their hydro-sedimentary characteristics. Despite different patterns were associated to each of the four identified clusters (e.g. different sediment loads and maximum suspended sediment concentrations), correlation between sediment origin and hydro-sedimentary variables was not significant due to the little seasonal variation in source type ascription. • Combination of continuous water and sediment monitoring with sediment fingerprinting were tested as catchment management tools. • The MixSIAR Bayesian mixing model and End Member Mixing Analysis showed similar results. • End Member Mixing Analysis provided valuable insights to determine dominant suspended sediment sources. • Source ascription homogeneity did not allow the link of hydro-sedimentary response to sediment source contributions. [ABSTRACT FROM AUTHOR]

Accelerated soil erosion by water has been identified as the most severe threat to soils across Europe. Land use and/or cover change and changing precipitation patterns are the main drivers for the loss of soil in agricultural landscapes. Soil erosion modeling allows to estimate the sediment yield and the effect of distinct agricultural land use practices on soil erosion. Additionally, under different climatic scenarios, soil erosion models can provide insights into future challenges and directions on how land use management and policy could be adapted. In this presentation, the main drivers of soil erosion processes in two small agricultural catchments in contrasting climatic regions (i.e. Mediterranean and Central European temperate climate) of Europe are identified. Furthermore, future climate scenarios, especially in terms of precipitation are investigated. The two small agricultural catchments are sub-catchments of the Fugnitz River in Lower Austria and the Na Borges River in the center of Mallorca, Spain. The widely used Water Erosion Prediction Project (WEPP) and its geospatial interface (GeoWEPP) application are utilized to model soil erosion processes on hillslope and sub-catchment scale. The input data needed to run the WEPP/GeoWEPP applications is topography, soil, land use and climate. Model verification and validation is realized by using event-based in situ data for individual hillslopes, based on high-resolution digital elevation models of difference compiled by aerial photography and terrestrial laser scanning. At catchment scale, the model calibration and evaluation are conducted with runoff and suspended sediment yield data. Geomorphologic and connectivity maps further support the validation of the modeled flow paths within the respective catchments.The soil erosion model identifies hotspot areas prone to high erosion rates and land use practices with high sediment loss; i.e. conventional tillage and monoculture. Different climate change scenarios elucidate how the soil erosion processes of these catchments in the two climatic regions are distinctly affected by changes in precipitation patterns, as the extent and the processes of soil erosion are depending on the environmental settings of the respective catchment. Our study further demonstrates the importance of studying soil erosion on small spatial scales with high resolution topography data, providing a better understanding of the main drivers of soil erosion in the investigated catchments helping to improvements in management practices and reduce soil erosion. [ABSTRACT FROM AUTHOR]