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12 Pags.- 5 Tabls.- 5 Figs., Several decades of intensive rainfed farming in Mediterranean mountains and later land abandonment has led to rapid land use and land cover changes. During recent centuries, the conversion of rangelands into croplands has increased the surfaces prone to erosion. In the southern Pre-Pyrenees, the process was reversed during the middle of the twentieth century, allowing the recovery of vegetation and subsequent variation in land cover. This work aims to assess how land use changes after generalised land abandonment affect some major soil properties related to soil quality. For this purpose, 98 replicate bulk soil samples were collected in a 23 km2 catchment that was mostly cultivated at the beginning of the last century. Soil samples were distributed over areas representing the main land uses (agricultural land, natural forest, pine afforestation and scrubland). Bulk density, stoniness, grain size, pH, carbonates, electrical conductivity, soil organic carbon (SOC), total nitrogen (TN), water retention capacity and magnetic properties (low frequency magnetic susceptibility (LF) and frequency dependence (FD)) were analysed in the samples from different land use areas. A past scenario was recreated using estimated data from the SPEROS-C model in order to evaluate changes in SOC over time. Furthermore, a multitemporal analysis of the Normalised Difference Vegetation Index of Landsat images was performed between 1972 and the present in order to assess the dynamics of revegetation. After land abandonment, 16.5% of the area remained as croplands, but afforestation and natural revegetation occupied 83.5% of the catchment. The highest mean value for SOC was found in the pine afforested area and the highest TN mean value was found in the natural forest. The lowest mean values for SOC and TN were recorded on the agricultural land. These results show the impact of soil changes produced by land use changes in fragile Mediterranean mountain agroecosystems., This research was financially supported by the project TRAZESCAR (CGL2014-52986-R) with the aid of a predoctoral contract (BES-2015-071780) funded by the Spanish Ministry of Science, Innovation and Universities.

46 Pags.- 8 Figs.- 5 Tabls. The definitive version is available at: https://www.sciencedirect.com/science/journal/03418162, Fallout radionuclides, such as Caesium-137, were proven to be a valuable means for studying medium-term (c.a. 50 years) soil erosion processes. In order to gain knowledge on the spatial distribution of 137Cs in volcanic soils of Andean Patagonia, 137Cs reference inventories were established along a precipitation gradient. At the subhumid sector, patterns of 137Cs gain/loss associated with land use were also determined considering native forests under grazing, a degraded rangeland and a pine plantation. Along the rising rainfall gradient (750–1400 mm), pedogenesis of volcanic ash soils, non-crystalline mineral formation, organic matter content and soil porosity varied, increasing in moister areas. Radionuclide inventories varied along the edaphoclimatic gradient, reaching mean values of 192, 267 and 576 Bq m−2, at study areas with 750, 950 and 1400 mm of annual precipitation, respectively. The 137Cs inventory followed an exponential relationship with precipitation, which could be related to the presence of allophane as the colloidal material in the soils from the rainiest area. The penetration depth reached by 137Cs varied between 15 and 25 cm, according to rain amount and soil texture. Most of the 137Cs fallout was retained in the uppermost 10 cm of the profiles and an exponential decline of 137Cs with depth, highly related to organic matter contents, was found. At the subhumid study area, both 137Cs mass activity and inventory, significantly decreased under the different land uses, with respect to reference soils. Although the pattern of 137Cs gain/loss varied according to topography, soil properties (organic matter and porosity) and vegetation cover, showing eroding and aggrading profiles, most samples had 137Cs values lower than the reference value, suggesting loss of soil as a consequence of erosion processes. Furthermore, as much as 45%, 58% and 70% of sample points from native forests, plantation and rangeland, respectively, had 137Cs values below the limit of detection. In the study transects, the loss of the upper 15 cm of soil in the subhumid sector during the last 50 years, highly exceeding tolerable erosion rates, highlights the urgent need for applying effective soil conservation measures. Reference inventories, which vary according to the edaphoclimatic gradient, and the loss of the radionuclide in sites with anthropic intervention, show the potential for using 137Cs measurements for assessing erosion processes in the Patagonian Andean Region., This research was funded by PICT-FONCyT 1715/10, CGL2014-52986-R and a Fellowship from Carolina Foundation. We aknowledge M. Calderón for his help with topographic fieldwork.

3. pdf files, with 1) Text (11Pags.); 2) Tabls. (5); 3) Figs. (4). The definitive version is available at: https://www.sciencedirect.com/science/journal/03783774, The aim of this research was to analyse the effect of rainfall intensity and slope on soil and nutrient losses by hydric erosion in soils with different hydrological characteristics. This research was carried out on soils collected from slopes with different land uses/covers (LU/LC) -forest, scrub, agricultural, afforested and barren land-, from a mountain area (Sierra de Santo Domingo in the South Pyrenean region), where intensive farming and land use changes including land abandonment and changes in soil cover have occurred. Soils were placed on erosion boxes (30 cm × 20 cm) and compacted to a bulk density similar to that measured in the field (slope values ranged between 10 and 20%). Soil properties such as organic matter content, soil texture and N and P contents were analysed (values used as concentration in the original soil). Soils were subjected to simulated rainfall with intensity values usually recorded in the area during storms. Runoff volumes were collected at 10 min intervals from the time that runoff was generated. The steady infiltration rate as well as the average runoff rates and soil losses were evaluated for each land use. In the runoff samples, sediment concentration and nutrients (N and P) were analysed using different aliquots. The comparative analysis of the results obtained under simulated rainfall in plots with soils from different land uses allowed determining the differences in contribution of each land use to soil and nutrient losses when they are subjected to similar rainfall intensities. The results showed that the maximum runoff rates were reached in agricultural soil and barren land after 40 min at low intensity and after about 20 min at high intensity. However, in soils under forest, scrub and afforestation, runoff rates were much lower for the same rainfall intensity and duration period. Soil sealing was the main factor reducing infiltration in the agricultural and in barren LU/LC soils, while in the other cases runoff was mainly produced after saturation. Soil losses were more than 10xtimes higher in barren land and in agricultural soils than in the other land uses. Nitrogen losses in agricultural soils were about 3 times higher than in forest, and scrub or in afforested LU/LC. Under high intensity rainfall, there was an enrichment ratio (ER) of nitrogen in the sediment in relation to the original soil, which was higher in scrub and agricultural lands (up to 1.33 and 1.32, respectively) than in the rest of land uses (1.1 on average). Phosphorous losses were mainly associated with soil particles and the land uses that gave rise to higher P losses was agricultural under any intensity, while P losses increased significantly in forest and afforested LU/LC at high intensity. The enrichment ratio (ER) was higher in agricultural soils (up to 1.82, increasing with intensity), forest and afforested LU/LC (1.33 and 1.16, respectively under high intensity) than in scrub (1.22) and barren lands (near 1). Information gained in this research can be of interest to manage mountain agroecosystems to limit N and P supply from headwaters to hydrological systems., This research is part of the project CGL2014-52986-R which was funded by the Spanish Ministry of Economy and Competitiveness.

11 Pags.- 2 Tabls.- 8 Figs., In Mediterranean mountain agroecosystems, soil erosion associated with the development of ephemeral gullies is a common environmental problem that contributes to a loss of nutrient‐rich topsoil. Little is known about the influence of ephemeral gully erosion on particle size distribution and its effect on soil organic (SOC) and inorganic (SIC) carbon among different sized soil particles in agricultural soils. In this study, laboratory tests were conducted using velocity settling tube experiments to examine the effects of erosion on sediment particle size distributions from an incised ephemeral gully, associated with an extreme event (235 mm). We also consider subsequent deposition on an alluvial fan in order to assess the distribution of SOC and SIC concentrations and dissolved carbon before and after the extreme event. Soil fractionation was carried out on topsoil samples (5 cm) collected along an ephemeral gully in a cultivated field, located in the lower part of a Mediterranean mountain catchment. The results of this study showed that the sediment transported downstream by runoff plays a key role in the particle size distribution and transportability of soil particles and associated carbon distribution in carbonate rich soils. The eroding sediment is enriched in clay and silt‐sized particles at upslope positions with higher SOC contents and gradually becomes coarser and enriched in SIC at the end of the ephemeral gully because the finest particles are washed‐out of the study field. The extreme event was associated with an accumulation of dissolved organic carbon at the distal part of the depositional fan. Assessment of soil particle distribution using settling velocity experiments provides basic information for a better understanding of soil carbon dynamics in carbonate rich soils. Processes of soil and carbon transport and relationships between soil properties, erodibility and aggregate stability can be helpful in the development of more accurate soil erosion models., This work was funded by the CICYT project(CGL2014-52986-R).

42 Pags.- 4 Tabls.- 6 Figs. The definitive version is available at: https://www.sciencedirect.com/science/journal/01671987, In this study, the potential effect of the selective transport and deposition by interrill erosion on the spatial distribution of eroded soil and associated soil organic (SOC) and inorganic carbon (SIC) in carbonate-rich soils was investigated in Mediterranean cultivated Calcisols. Particular attention was paid to the role of calcium carbonate in the stabilization of SOC and its impact on soil structure and the settling behavior of soil particles in suspension. The settling velocity is a key variable in controlling the transport and fate of eroded sediment and sediment-associated carbon, which accounts for soil particle / aggregate size and density. The objectives were to analyze the settling behavior of cultivated soils at two contrasting slope positions, representative of erosion and deposition sites, in an interrill area and compare with those of uncultivated and undisturbed soils (not affected by deposition or erosion processes). Besides we examined the distribution of SOC and SIC associated with different particle size classes. Soils were fractionated into five size classes (>250, 125–250, 63–125, 32–63 and ≤32 μm) using a settling tube procedure and carbon contents (SOC and SIC, %) were measured at each settling size classes. The results indicated that the particle size selectivity of interrill erosion affects the distribution of soil particles and associated SOC and SIC spatial variability. As a result of erosion processes, cultivated soil at the upper part of the slope was enriched in finer fractions compared to the lower part where mainly coarse particles were deposited and the finer material was transported and washed out. Cultivation leads to a depletion of SOC and of the >250 μm fraction in comparison with uncultivated and undisturbed soil, where the SOC content was two times higher than in cultivated soil. Lighter and smaller settling size classes (≤63 μm) had the highest SOC content in uncultivated and cultivated downslope soils. This is contrary to what occurs with SIC that acts as a cementing agent and promotes aggregation formation affecting soil structure. Therefore, sand-sized and silt-sized carbonates were accumulated in coarser size fractions in these soils, mainly in downslope positions. This study provides a first insight into the role of selective processes by interrill erosion and their impact on soil organic/inorganic carbon distribution affected by different particle selective transport process, soil aggregate size distribution and associated carbon in Mediterranean agroecosystems., This work was funded by the CICYT project (CGL2014-52986-R).

38 Pags.- 5 Figs.- 3 Tabls. The definitive version is available at: https://www.sciencedirect.com/science/journal/03418162, Patterns of erosion, transport and deposition of soil particles not only affect the distribution of mineral fraction of the soil but their organic components. The spatial variability of soil nutrients in Mediterranean mountain agroecosystems that combine complex land uses and abrupt topography is poorly documented despite emerging concerns on nutrients fate require understanding the potential impact of soil erosion on nutrients redistribution across landscapes. This study aims to assess at catchment scale the spatial patterns of soil organic and inorganic carbon (SOC, SIC), soil organic carbon fractions and total nitrogen (TN) in relation to land uses and soil redistribution. To this purpose we selected a well characterized endorheic catchment located in NE Spain where soil erosion and deposition rates derived from 137Cs measurements were previously documented and we mapped the distribution of cropland and rangeland areas. A grid of 100 × 100 m was established for collecting a total of 205 soil samples for nutrients and standard soil analyses. In both rangeland and cropland the patterns of SOC and TN stocks were clearly related to 137Cs inventories thus significantly lower nutrient stocks (SOC: 34.1 ± 18.6 Mg ha−1, TN: 2.9 ± 1.7 Mg ha−1) were found in erosional sites whereas higher stocks (SOC: 44.9 ± 24.2 Mg ha−1, TN: 3.9 ± 2.3 Mg ha−1) were recorded in depositional areas. In cropland the mean nutrients contents (SOC: 1.1 ± 0.8%, TN: 0.1 ± 0.1%) were significantly lower than in rangeland (SOC: 3.2 ± 2.1%, TN: 0.2 ± 0.1%). The highest C/N ratios (29) were found in rangeland, while in cropland they occurred in depositional areas with their values below 10 in the erosional sites. In turn, the SIC content (range 0.4 to 10.2%) was slightly lower at the depositional sites (4.9 ± 2.2%) but not significantly different from the erosional sites (5.1 ± 2.2%). Cultivated and steep slopes led to loss of soil and nutrients due to intense erosion processes also related to tillage and crop productivity. Our findings provide evidence that the combined effect of land use and soil redistribution exert an important control on the spatial distribution of nutrients, highlighting a significant decrease of SOC and TN stocks with increasing soil erosion in croplands. The information gained achieves a better understanding of soil nutrients dynamics and further knowledge for effective land management of mountain agroecosystems in the Mediterranean region., This research was funded by the project (CGL2014-52986-R) of the Spanish Ministry of Science, Innovation and Universities.