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Abstract Dissolved solids (DS) and suspended sediment (SS) loads are considered relevant environmental problems. They are related to a wide range of on-site and off-site impacts, such as soil erosion or salinization of water bodies. In this study, the dynamics of DS and SS concentrations and loads were assessed in five small watersheds covering representative agricultural land uses in Navarre (Spain). To this end, discharge, DS and SS concentration data were collected during ten hydrological years at each watershed outlet, and loads were computed from discharge and concentration values. DS concentration followed a seasonal pattern imposed by the availability of water, with higher concentrations recorded in low-flow periods and lower concentration in the high-flow period. SS concentration was extremely variable, with a range of 2–4 orders of magnitude in concentration for any specific discharge. Temporal variations (both intra- and inter-annual) in DS loads were explained by differences in runoff, whereas those of SS were not, being the SS loads associated mainly with specific high flow events. These temporal patterns were observed for both agricultural (this study) and non-agricultural (literature) watersheds. From the data in the Navarrese watersheds and those available in the literature, we inferred that agricultural land use, in general, tends to increase the concentration of both DS and SS. Regarding DS and SS yields, the effects of agricultural land use on DS yields are controlled by the changes in runoff rather than the (small) changes in DS concentration. In this sense, land uses changes expected to increase runoff (i.e., a shift from forested to arable or from rainfed to irrigated agriculture) would increase DS yields. On the other hand, agricultural land use tends to increase SS yields, although the effect is highly variable depending on site-specific factors, both natural (e.g., watershed shape) and anthropogenic (e.g., degree of soil conservation practices). In the Navarrese watersheds, DS yields ranged from 1.1 to 2.2 Mg ha−1 year−1 whereas SS yields ranged from 0.3 to 4.3 Mg ha−1 year−1. DS yields seem to dominate under non-agricultural conditions and in most agricultural land uses at the small watershed scale. On the other hand, SS yields dominate in watersheds with increased soil erosion as a consequence of arable land use over erosion-prone watersheds. Highlights • Dissolved solids concentration follows a seasonal pattern. • Suspended sediment concentration was extremely variable. • Dissolved loads behave conservatively with water. • The dissolved load dominated the exportation in most of the cases. • Agricultural land use increases suspended sediment concentration and loads. [ABSTRACT FROM AUTHOR]

Changes in land use related to mining in the north-western mountains of Spain are analysed. We studied 15 representative types of mining activity in the Sil River basin (León province), including three types of mineral resources: gravel, roofing slate and coal. We use colour orthopothos of 2014 to calculate areas occupied by dumps, lagoons, open pits, auxiliary construction and access roads in mines. Also areal photographs of 1956–1957 were used to measure land uses in these years. In all cases the extraction of mineral resources by surface mining has caused the destruction of the former topography, and these alterations are irreversible. The new post-mining topography represents a drastic change in the landscape and land use in these areas. Areas occupied by coal and slate mining (around 1500 ha.) are significantly greater than gravel quarries (74 ha.). Waste material is greater in slate mining (69%) and coal mining (44%) than in gravel mining (8%). Former agricultural areas now occupied by mining were more extensive in gravel quarries (44%) than in slate quarries (10%) and coal mines (6%) because of the gentler topography in the areas where the gravel quarries are located. In six cases mining are located in natural protected areas and in other cases alter and/or eliminate valuable geological heritage. [ABSTRACT FROM AUTHOR]

Universal Soil Loss Equation USLE-based erosion models have been used extensively to complement erosion measurements, to understand the interactions of the different geophysical features into erosion processes and to assess adequate alternative management practices and scenarios analyses. Despite its proved usefulness on different land-uses around the world, there is an urgent need to set up simple tools which do not require an advanced management expertise in terms of both choose of model parameters and calculation ability and which are accurate particularly at the event scale. In this paper the suitability of the Modified USLE (USLE-M) model at the event and the annual scale were evaluated in an olive orchard catchment of 6.1 ha in Spain where a rainfall-runoff-sediment yield dataseries of over 8 years (2005–2013) was available. The model was applied dividing the catchment into morphological units, i.e. areas having a defined aspect, length and steepness. In addition, different model parameterizations of both the crop factor of the Revised USLE factor and β-coefficient of the sediment delivery ratio of each morphological unit were studied in order to describe the seasonal variability of soil conditions along the year. At event scale the best performance of the USLE-M model was obtained using a single value of the β coefficient equal to median value β e,m without considering the seasonal variability of crop factor since it is well-represented by the term rainfall-runoff erosivity index. At the annual scale, the calculation of crop factor values provided a good model performance in estimating sediment yield, with a coefficient of efficiency of 0.96. The analysis demonstrated that the USLE-M model was a useful tool to simulate soil losses at the event and annual scales and its application might provide guidelines for other users. [ABSTRACT FROM AUTHOR]

The knowledge of soil salinity and the temporal changes of its distribution in the soil profiles can give warnings for the protection of saline habitats. This study described and compared the salinity profiles of the soils from four hypersaline wetlands at inland, ill-drained depressions in NE Spain, which were sampled throughout the year in 1979–1980 and 1999–2000, and differed in land use. The halophytic communities dictated the location of sampling sites. After the saturated pastes of 404 soil samples were prepared, the electrical conductivity of the extracts (ECe) and the concentrations of major ions were measured, and additional supplementary analyses were performed. A subset of the samples was titrated for calcium carbonate equivalent and gypsum content. ECe and ion concentrations calculated for synthetic soil layers facilitated the comparisons of the vertical distribution of soil salinity among dates, depths, and sites. The shape of the mean ECe profiles over all sampling dates indicated moderate differences between the two wetlands closest to each other, Plan de Callén (PC) and Paúl de Almuniente (AL), which had similar (< ~ 10 dS m − 1 ) ECe. In contrast, the ECe profile at Paúl de Anzano (AN) ranged from 40 dS m − 1 to 50 dS m − 1 in the upper meter of the soil, which decreased steadily to 20 dS m − 1 at a 2-m depth. At Saladar de Agustín (AG), ECe was much higher and the profile had the opposite shape, ECe ~ 55 dS m − 1 at the surface and > 80 dS m − 1 at an 80-cm depth. The shape of ECe profiles at AL, PC, and AG was rather stable over time, contrasting with the measured desalination of the soil at AL after its conversion into a rice paddy. The changes in the sodium adsorption ratio (SAR) in the soil profiles at AN, PC, and AL are indicators of the potential extremes in the hydric behavior of the soils. At AG, the mineralogical clays are a minor component of these gypseous soils; therefore, the SAR, only, was used as a measure of the relative concentrations of Na + versus Ca 2 + plus Mg 2 + . The median SAR of all AG soil samples did not differ significantly among sampling sites or dates. The shorter sampling depth intervals used in 1979–80 were responsible for the greater spread in the distribution and the increase in extreme SAR values compared to the data collected in 1999–2000. [ABSTRACT FROM AUTHOR]

• We used suspended sediment data during a period of consecutive explosive cyclogenesis. • Spatial land use plays an important role in the suspended sediment yield. • Sediment concentrations are largely dependent on sediment depletion during the previous events. During the winter of 2013/2014, a sequence of explosive cyclogeneses occurred in NW Spain, causing severe flooding and substantial economic damage. Peak discharges were extremely high in many areas, with return periods in excess of 2–5 years. The heavy flow registered during these episodes provides a unique opportunity to evaluate the sedimentological effects resulting from high-magnitude flow events. Such events are relatively rare and the technical difficulties in sampling with sufficiently high frequency means that few observations on sediment transport can be gathered during the same. In this study, we present detailed hydrological and sedimentological observations across a period of consecutive explosive cyclogeneses from two small-sized catchments (i.e., the Corbeira stream and headwater of the Mero river) located in Galicia (NW Spain), in order to examine the factors controlling suspended sediment (SS) dynamics during high-magnitude flow events. The study sites are representative of the biophysical conditions (e.g. rainfall pattern, land use, vegetation cover and management practice) in NW Spain. The catchments of the Corbeira stream and headwater of the Mero river are similar with respect to climate, land use and management practice. The main differences are the distribution of land use and catchment size (Corbeira: 16 km2 and Mero: 65 km2). Large amounts of sediment were transferred in both catchments in response to flow events. A high variability in SS load during these was also observed in the two catchments, which is attributed to variation in rainfall characteristics, magnitude peak discharge, antecedent conditions controlling sediment availability, and suggests that sediment supply and transport vary widely over time. Higher concentration and variability of SS was observed in the Corbeira catchment. Differences in SS dynamics were also noted between the catchments that may be attributed to differences in the spatial distribution of land use, which influence the location of the erosion source and SS availability, and directly and indirectly affects connectivity between the sediment source area and the stream. In the Corbeira catchment, the SS load was closely linked to the hydrological response and rainfall, whereas in the Mero basin, preceding conditions, i.e. the sediment depletion during the previous events, played an important role. The results demonstrated that peak SS concentrations may coincide with, or lag behind, peak discharge, and factors other than discharge (mainly the location of the sediment source and its connectivity with the drainage network) have a major influence on SS concentrations. [ABSTRACT FROM AUTHOR]

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. • Soil redistribution and land use are key factors on nutrients stock. • Highest SOC and TN stocks occur in cropland at depositional sites. • Labile carbon is more sensitive than stable fraction to soil erosion and land use. • Cropland lowlands are important sinks of soil inorganic carbon. • 137Cs data help to understand soil nutrients pools in Mediterranean agroecosystems. [ABSTRACT FROM AUTHOR]

Abandoned fields form an integral part of the landscape of Mediterranean mountains. For centuries, very steep slopes with poor soils were cultivated to feed the local population. From the mid-20th century, agriculture on many slopes has been abandoned and secondary succession is taking place with environmental, socio-economic and landscape implications. This paper investigates the role of physical (climate variability and topography) and human (age of abandonment and field type - flat, sloping, terraced) factors in the process of secondary succession in abandoned fields in a representative Mediterranean mountain area. Aerial photographs from 1956 and 1978 were used to map the space-time process of land abandonment, and field types. Data on vegetation cover in abandoned fields was obtained in the SIOSE, the information system on land use in Spain (2006). The map was incorporated into a GIS and statistical analysis was done with R software (R, version 3.2.3). The results show that altitude and climate variability are the principal factors explaining the distribution of areas of forest and shrub. The slope and solar radiation are less important. Human management, although apparently a lesser determinant, has a strong influence. Management before abandonment conditions the spatial distribution of the seed bank and the extent of soil degradation. Management following abandonment (afforestation of conifers, shrub clearings and livestock grazing) decides where pine forest and pastures are located. The results of our case study suggest, that unlike most of cases in the literature, the age of abandonment is not the main factor explaining the natural succession processes. The knowledge about how natural and anthropogenic factors affect secondary succession should be considered a tool for land management in mountain areas. • We study the factors explaining the process of plant colonisation in abandoned fields. • Mapping of old cultivated, abandoned areas and land covers were carried out. • Altitude and climate are the main factors explaining land cover distribution. • Human management (age of abandonment and field types) has a strong influence. • Management after abandonment decides where pines and pastures are located. [ABSTRACT FROM AUTHOR]