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Small headwater catchments deliver large quantities of suspended sediment (SS) to the ocean. However, there are relatively few studies focused on the study of patterns and dynamics of suspended sediment in headwater catchments over the long-term (10 year or more). In this study, the dynamics of suspended sediment transport were examined at different time scales in a small headwater catchment in NW Spain, based on a 12-year dataset from high-resolution monitoring. The results revealed that, similar to other humid catchments, the hydrological response was highly dependent on initial conditions, especially in autumn and summer. However, in winter and spring the hydrology was more influenced by rainfall amount. The annual suspended sediment was 117 Mg, which equates to a suspended sediment yield of 10 Mg km −2 y −1 . The SS yield in the Corbeira catchment is related to runoff generation and flooding, which play a key role in sediment yield from the catchment. About 80% of the annual SS was transported over 12% of the study period. Rainfall and discharge at the beginning of the events were the most important factors in explaining the hydrological response at event scale. Suspended sediment transport in this catchment is determined by event magnitude, while the SS is mainly influenced by variables related to runoff erosivity.

Paper of 6th World Multidisciplinary Earth Sciences Symposium 7-11 September 2020, Prague, Czech Republic [Abstract] Understanding both the concentration and distribution of aluminum (Al) in agricultural soils is essential to provide a benchmark on the productivity of such soils. In this study, a combination of sequential chemical extraction and mineralogical investigation of the fine fraction was used in order to evaluate Al pools in agricultural soils in Galicia (NW Spain), an Atlantic European region where the wet climate favors leaching of soil basic cations. Determination of Al (soluble/exchangeable/specifically adsorbed, bound to manganese oxides, associated with amorphous compounds, bound to oxidizable organic matter, associated with crystalline iron oxides, and residual fraction) in the topsoil samples was performed to evaluate its potential environmental availability in the study area. Aluminum contents were determined by flame atomic absorption spectrophotometry and the mineralogy of the fine fraction of these soils was studied by X-ray diffraction (XRD). The results showed that Al is mainly in the residual phase, which represents Al incorporated in the lattice minerals, and consequently the threat of toxicity to plants and the environment is reduced. The XRD results showed the presence of hydroxy-Al interlayered vermiculites and kaolinite, accompanied by small amounts of goethite, mica, and quartz. This paper is a contribution to the Project CGL2014-56907-R of the National Program of Research, Development and Innovation Oriented to the Challenges of Society, which was funded by the Spanish Ministry of Economy and Competitiveness. M. L. Rodríguez-Blanco has been awarded a postdoctoral research contract (Juan de la Cierva Programme), which was funded by the Spanish Ministry of Economy and Competitiveness.

Producción Científica, Observational trend analysis is fundamental for documenting changes in river flows and placing extreme events in their longer-term historical context. Observations from near-natural catchments, i.e., with little or no alteration by humans, are of great importance in detecting and attributing streamflow trends. The purpose of this study is to analyze the annual and seasonal trends of stream discharge (mean, low and high flows) in a headwater catchment in NW Spain, i.e., in the wettest corner of the Iberian Peninsula. The results showed no significant decrease in the mean annual stream discharge. However, significantly lower summer and autumn mean stream discharge and an increase in low flow period were detected, in addition to lesser autumn high flow. The rainfall pattern followed an upward trend, but was not significant. This different pattern shown by rainfall and discharge indicates that is not sufficient to explain the observed trend in stream discharge. Air temperature, most notably by enhancing evapotranspiration, may explain the altered patterns of stream discharge., Xunta de Galicia (Proyecto CGL2014-56907-R), Ministerio de Economía, Industria y Competitividad (Proyecto CGL2014-56907-R)

Understanding the metal dynamics in natural waters is critical to assessing the process and flow pathways that deliver these constituents to the stream network. Metal dynamics can be addressed by an analysis of concentration-discharge relationship across a large spectrum of hydrological conditions. However, metal-discharge responses have only been studied in detail for short periods or a few selected events. In this study, a detailed analysis of the hysteresis loops exhibited by metal concentration-discharge relationship was undertaken to assess the Al, Fe, Mn and Cu dynamics and factors controlling changes in metal concentrations in a small scale rural catchment. Metal (sediment-associated and dissolved) concentrations were measured at high temporal resolution during storm events in a small rural headwater catchment in Galicia (NW Spain). Hysteresis analysis indicated a contrasting concentration-discharge dynamic for sediment-associated and dissolved metals, highlighting a strong decoupling between the two due to their different sources or delivery pathways. For sediment-associated metals, clockwise hysteresis (56%) was the predominant pattern, highlighting the rapid sediment-associated metal mobilisation via surface runoff from sources located near the stream channel. In contrast, dissolved metal showed predominantly anticlockwise hysteresis (58% of storm events), emphasising the role of subsurface flow and soil leaching processes. The different flushing mechanisms between sediment-associated and dissolved metals imply that different catchment management strategies should be implemented for the control of metal export.

[Abstract] The content of metals in soils depends on the combined effect of several factors, which include the properties of the metals themselves and their concentrations in the soil, environmental conditions and soil components. Topsoil samples from different plots of a rural area, which combines reforestation (forests soils) with agriculture (pasture and cultivation soils) and livestock in the Galicia region, NW Spain, were analyzed for total Cu and Zn, pH, organic matter content, and particle size distribution. The geological substrate of the study area is mainly biotitic schist. The aims of this study were to investigate the total Cu and Zn concentrations in the topsoil samples, and to examine the relationship of these metals with the mentioned physicochemical properties using a correlation analysis. Soils were characterized by conventional analytical methods. Total Cu and Zn contents were determined by atomic absorption spectrophotometry after wet digestion with a hot mixture of nitro-perchloric-hydrofluoric acids. The results showed that the soils have on average moderately acid pH, considerable organic fraction and clay loam texture. The total Cu and Zn concentrations were low (mean about 25 mg kg-1 and 78 mg kg-1 respectively), which reveals that these topsoils are not contaminated. The statistical analysis showed positive correlations between the sum of the clay and silt contents, and the total Cu and Zn concentrations. There are no significant correlations between total Cu and Zn, and organic matter content. Xunta de Galicia; 10MDS103031 Ministerio de Economía y Competitividad; CGL2014-56907-R

Este artículo contiene 16 páginas, 6 figuras, 2 tablas., Soil degradation by water is a serious environmental problem worldwide, with specific climatic factors being the major causes. We investigated the relationships between synoptic atmospheric patterns (i.e. weather types, WTs) and runoff, erosion and sediment yield throughout the Mediterranean basin by analyzing a large database of natural rainfall events at 68 research sites in 9 countries. Principal Component Analysis (PCA) was used to identify spatial relationships of the different WTs including three hydro-sedimentary variables: rainfall, runoff, and sediment yield (SY, used to refer to both soil erosion measured at plot scale and sediment yield registered at catchment scale). The results indicated 4 spatial classes of rainfall and runoff: (a) northern sites dependent on North (N) and North West (NW) flows; (b) eastern sites dependent on E and NE flows; (c) southern sites dependent on S and SE flows; and, finally, (d) western sites dependent on W and SW flows. Conversely, three spatial classes are identified for SY characterized by: (a) N and NE flows in northern sites (b) E flows in eastern sites, and (c) Wand SW flows in western sites. Most of the rainfall, runoff and SY occurred during a small number of daily events, and just a few WTs accounted for large percentages of the total. Our results confirm that characterization by WT improves understanding of the general conditions under which runoff and SY occur, and provides useful information for understanding the spatial variability of runoff, and SY throughout the Mediterranean basin. The approach used here could be useful to aid of the design of regional water management and soil conservation measures., This research was supported by projects funded by the MINECOFEDER: CGL2014-52135-C3-3-R, CGL2014-59946-R, CGL2015-65569- R, CGL2015-64284-C2-2-R, and PCIN-2017-061/AEI. When this manuscript was first submitted Estela Nadal-Romero and Damià Vericat received a “Ramón y Cajal” postdoctoral contract (RYC-2013-14371 and RYC‐2010‐06264, Spanish Ministry of Economy and Competitiveness, MEC). Damià Vericat is now a Serra Húnter Fellow at the University of Lleida. María Fernández-Raga received a “José Castillejo” postdoctoral grant (Spanish Ministry of Education, Culture and Sports). Carla Ferreira was supported by a post-doctoral research grant from the Portuguese Science and Technology Foundation (SFRH/ BPD/120093/2016). Mariano Moreno-de las Heras received a Juan de la Cierva postdoctoral contract (IJCI-2015-26463) from the MEC. José Andrés López-Tarazón received a Vicenç Mut postdoctoral fellowship from the Autonomous Balearic Government (CAIB PD/038/2016). José Andrés López-Tarazón and Ramon Batalla also acknowledge the Secretariat for Universities and Research of the Department of the Economy and Knowledge of the Autonomous Government of Catalonia for supporting the Consolidated Research Group 2014 SGR 645 (RIUSFluvial Dynamics Research Group), and the CERCA Programme. This paper has benefited from the Lab and Field Data Pool created within the framework of the COST action CONNECTEUR (ES1306).

Transport of suspended sediment (SS) and phosphorus (P) via surface runoff from soils to surface waters is a major problem of water quality degradation in many European rivers and in other parts of the world. This problem is especially serious during wet periods, which can produce twice the P loads of dry periods. In this study, the SS load and particulate phosphorus (PP) exported from a small catchment located in NW Spain (in which cultivated soils had different degrees of vegetation cover) were analyzed during two rainy periods of February 2006 and February 2007. The SS and PP loads were calculated from the data of discharge, and SS and PP concentrations were measured in water samples collected at the catchment outlet. SS and PP loads were higher in 2006 than in 2007, while there was higher rainfall and stream flow in 2007. Differences in the degree of vegetation cover in the cultivated fields with good connectivity with the stream, which was the main source area of sediment in this catchment, e...

Land use may modify certain soil properties while soil physicochemical characteristics can influence metal partitioning in soils. Therefore, the total content and various forms of aluminum (Al) in solid phase of schist-developed topsoils (0–20 cm) in NW Spain under different land uses (i.e., forest, pasture, and cultivation) were evaluated to identify the Al-bearing phases. Aluminum fractionation was performed, using a six-step sequential extraction procedure with ammonium acetate, hydroxylamine hydrochloride, ammonium oxalate in darkness, hydrogen peroxide, ammonium oxalate under ultraviolet radiation, and acid digestion. Mean concentrations of total Al were similar in the soils under three land uses. Mean percentage of the various Al forms in all soils were in the following order: residual fraction > amorphous compounds > crystalline compounds > water-soluble/exchangeable/specifically adsorbed > bound to oxidizable organic matter > manganese oxides. The forest soils contained considerably higher...

Comprehensive studies that examine the transfer of metals across soil-river bed sediment systems at the basin scale are scarce. An understanding of the distribution of metals among various fractions of soils and sediments within a basin is fundamental to understand their environmental behavior and, thus, to define watershed management plans. This study aims to determine the distribution of metals (Fe, Mn, Cu, and Zn) in topsoils under different land uses (cultivation, pastures, and forests) and river surface sediments in the upper Mero River basin (NW Spain) and to assess these metals' mobility and bioavailability in both environmental compartments to detect potential threats to crops and the water quality. Sequential extraction is used to fractionate the four metals into six fractions: soluble/exchangeable/specifically adsorbed, metals that are bound to Mn oxides, amorphous compounds, metals that are bound to organic matter, crystalline Al and Fe oxides, and residual metals (metals within the crystal lattices of minerals). The fractionation results for both soils and sediment indicate an abundance of metals in the residual fraction (except for Mn in soils) followed by relatively high percentages of oxide-bound fractions (mostly crystalline Fe oxides for both Fe and Zn, amorphous for Cu, and Mn oxides for Mn). On average, the Mn residual fraction in soils (30.2%) is only slightly exceeded by the Mn oxide fraction (34.7%). The land uses do not affect the sequence of metal-binding phases in soils, except for Mn, which is only slightly altered. The results also suggest that Fe, Mn, Cu and Zn in both soils and sediments are not readily mobile under current environmental condition and hence pose no threat to crops or the water quality. In overall terms, the mobility and bioavailability of the four metals (considering the sum of the three least mobile fractions, namely, organic matter, crystalline Al and Fe oxides, and residual) in the soils decrease in the following order: Mn > Cu > Fe > Zn. The same sequence occurs in the sediments, but the order between Fe and Zn is reversed. The soils and sediments that are studied cannot be considered polluted in terms of these metals because of their low levels and prevalence in the residual fraction, which is typical of contributions from natural sources and indicates the pedogenic/lithologic origin of these metals.

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.

This study assesses the possible use of suspended sediment as an indirect measurement of phosphorus (P) concentrations in a rural headwater catchment located in NW Spain. Particulate P accounted for about 70 percent of the P export, indicating that P transport is linked to sediment in this catchment. The relationship between P and suspended sediment concentrations showed that particulate P was strongly dependent on suspended sediment, although the relationship is not consistent throughout seasons. The particulate P–suspended sediment relationship behaved differently at low flow and runoff events; the relationship was only significant during runoff events. This is because low flow is dominated by dissolved P and by pathways that do not mobilize or transport sediment. The particulate P–suspended sediment ratio was lower during runoff events than during low flow, which is consistent with enrichment ratio effects.

Nadal-Romero...[et.al.], Precipitation has been recognized as one of the main factors driving soil erosion and sediment yield (SY), and its spatial and temporal variability is recognized as one of the main reasons for spatial and temporal analyses of soil erosion variability. The weather types (WTs) approach classifies the continuum of atmospheric circulation into a small number of categories or types and has been proven a good indicator of the spatial and temporal variability of precipitation. Thus, the main objective of this study is to analyze the relationship between WTs, runoff, soil erosion (measured in plots), and sediment yield (measured in catchments) in different areas of the Iberian Peninsula (IP) with the aim of detecting spatial variations in these relationships. To this end, hydrological and sediment information covering the IP from several Spanish research teams has been combined, and related with daily WTs estimated by using the NMC/NCAR 40-Year Reanalysis Project. The results show that, in general, a few WTs (particularly westerly, southwesterly and cyclonic) provide the largest amounts of precipitation; and southwesterly, northwesterly and westerly WTs play an important role in runoff generation, erosion and sediment yield as they coincide with the wettest WTs. However, this study highlights the spatial variability of erosion and sediment yield in the IP according to WT, differentiating (1) areas under the influence of north and/or north-westerly flows (the north coast of Cantabria and inland central areas), (2) areas under the influence of westerly, southwesterly and cyclonic WTs (western and southwestern IP), (3) areas in which erosion and sediment yield are controlled by easterly flows (Mediterranean coastland), and (4) lastly, a transitional zone in the inland northeast Ebro catchment, where we detected a high variability in the effects of WTs on erosion. Overall results suggest that the use of WTs derived from observed atmospheric pressure patterns could be a useful tool for inclusion in future projections of the spatial variability of erosion and sediment yield, as models capture pressure fields reliably. © 2014 Elsevier B.V., Support for this research was provided by the projects: HIDROCAES (CGL2011-27574-C02-01 and 02), INDICA (CGL2011-27753-CO2-01 and 02), and CGL2010-21754-C02-01 of the Spanish Ministry of Science and Technology funded by the Spanish Ministry of Economy and Competition and FSE. Thanks to the AEMeT for the rainfall data, and to Roberto Serrano for his helpful assistance in the precipitation analysis. Thanks to the reviewers and the editor for their detailed work to improve this article. E. Nadal-Romero was the recipient of a research contract (Spanish Ministry of Economy and Competition, Programme Juan de la Cierva), and now she is a Marie Curie postdoctoral researcher supported by the UE (project “MED-AFFOREST” PIEF-GA-2013-624974).

The temporal variability in nitrogen (N) transport in the Corbeira agroforestry catchment (NW Spain) was analysed from October 2004 to September 2008. Nitrate (NO3–N) and total Kjeldahl nitrogen (TKN) loads and concentrations were determined at various timescales (annual, seasonal and event). The results revealed a strong intra-annual and inter-annual variability in N transport influenced by weather patterns and consequently by the hydrological regime. Mean annual export of total N in the catchment was 5.5 kg ha−1 year−1, with NO3–N being the dominant form. Runoff events comprised 10% of the study period but contributed 40 and 61% of the total NO3–N and TKN loads, respectively. The NO3–N and TKN concentrations were higher during runoff events than under baseflow conditions, pointing to diffuse sources of N. The mobilization of TKN during runoff events was attributed to surface runoff, while NO3–N might be related to subsurface and groundwater flow. Runoff events were characterized by high variability in N loads and concentrations. Higher variability was observed in N loads than in N concentrations, indicating that event magnitude plays an important role in N transport in this catchment; event magnitude explained approximately 96% of the NO3–N load. However, a combination of variables related to runoff event intensity (rainfall, discharge increase and kinetic energy) explained only 66% of the TKN load. Copyright © 2014 John Wiley & Sons, Ltd.

Monitoring was conducted in a basin with a history of agricultural pollution (mainly due to the spreading of livestock slurry) to evaluate the response of stream water ion concentrations to the change from agricultural land use to forest. We measured pH, electrical conductivity (EC), and major dissolved elements [phosphate (PO4) phosphorus (P), nitrite (NO2) nitrogen (N), nitrate (NO3) N, ammonium (NH4) N, silicon (Si), sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), sulfate (SO4), and chloride (Cl)] in the stream water during the period 1997–2002 at irregular time intervals. Median values were significantly greater in the agricultural period than in the forest period (P

This study determines the seasonal variability of metal partition coefficients [aluminium (Al), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn)] and analyses the importance of suspended sediments (SS), dissolved organic carbon (DOC) concentrations, pH, and discharge (Q) on the seasonal variability of metal partition coefficients (KDs) in the headwaters of the Mero River catchment, which drains an agroforestry area in northwestern Spain. Metal partition coefficients were used as an approach to relate dissolved and particulate fractions. Water samples were collected over 3 years (2005–2008) at the catchment outlet. The mean metal dissolved concentrations were: Fe (43.5 μg L−1) > Al (23.3 μg L−1) > Zn (1.8 μg L−1) > Mn (1.2 μg L−1) > Cu (0.3 μg L−1). Partition coefficients followed the order Mn > Al > Fe > Zn > Cu, and their values exhibited low variability. Al, Cu, and Zn partition coefficients presented the greatest values in summer, except during 2007–2008, when the greatest KDs value was observed i...

Pollution assessment in a given area depends mostly on the precise determination of the so-called background values. In this work, enrichment factors (EFs) for iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in suspended solids (SS) of a stream draining a rural catchment (NW Spain) were determined to assess whether the observed concentrations of these metals represent natural or contaminated levels. Aluminum was used as a normalizer element. Four approaches were used for defining background values used in the EF analyses: a local background value for metals concentrations in SS, a local background value for metals concentrations in C-horizon soils, mean crust values, and mean shale values. The most satisfactory result was obtained when using local background values for metals concentrations of SS, suggesting that on average the Fe, Mn, Cu, and Zn concentrations measured represent natural levels. However, some signs of enrichment were observed (16–28 percent of the samples with EF > 1.5).

In this study, the concentrations and loads of different forms of nitrogen [nitrate nitrogen (NO3-N), total Kjeldahl nitrogen (TKN), and total nitrogen (TN)] in the headwater catchment of the Mero River (NW Spain) were analyzed. The TN concentrations were relatively low (mean: 2.57 mg L−1). Nitrate was the predominant form of N in the Mero catchment, accounting for 76.65 percent of the TN concentration. Measured NO3-N concentrations were always lower than the maximum allowed drinking water concentration. An annual TN load of 61.2 Mg was computed, representing an export of 0.94 Mg km−2 y−1, whereas annual exports NO3-N and TKN were of 0.79 and 0.15 Mg km−2 y−1, respectively.

Hydrological signatures are indices that help to describe the behavior of catchments. These indices can also be used to transfer information from gauged to ungauged catchments. In this study, different approaches were evaluated to determine volumetric runoff coefficients in 18 small/medium experimental gauged catchments of the Iberian Peninsula and to fit runoff calculations based on precipitation data for gauged and ungauged catchments. Using data derived from 1962 events, rainfall-runoff relationships were characterized and compared in order to evaluate the various hydrological response patterns. Volumetric runoff coefficients and cumulative runoff and precipitation ratios of the events that generated runoff (R cum ) minimized the root mean square error. A linear fit for the estimation of R cum in ungauged catchments was based on mean annual precipitation, rates of infiltration, the fraction of forest-land use, and the catchment channel length. Despite high catchment heterogeneity, R cum resulted in a suitable parameter to evaluate hydrological variability in rural gauged and ungauged catchments. In 50% of the catchments, the precipitation accounted for less than 50% of the runoff variation. Annual precipitation, antecedent rainfall, and base flow did not have a high significance in rainfall-runoff relationships, which illustrates the heterogeneity of hydrological responses. Our results highlight the need for signature characterizations of small/medium rural catchments because they are the sources of runoff and sediment discharge into rivers, and it is more economical and efficient to take action to mitigate runoff in rural locations., This research was supported by the research projects CGL2015-64284-C2-2-R, CGL2015-64284-C2-1-R, CGL2014-52135-C3-3-R, CGL2015-65569-R, CGL2014-56907-R, and AGL2015-65036-C3-1 funded by the MINECO-FEDER (Spanish Ministry of Economy and Competitiveness). E.N.-R. is the beneficiary of a Ramón y Cajal postdoctoral contract (Spanish Ministry of Economy and Competitiveness).

This paper examines sediment and metal (Al, Fe, Mn, Cu, and Zn) exportation at different timescales (annual, seasonal and event) during a 3-year period (2005–2008) in the Mero River headwater, a rural catchment under humid temperate climate. Interannual differences were found both in annual loads and their distributions throughout the year. At annual scale, sediment and particulate metal loads followed the same trend as streamflow, while dissolved metals showed different patterns. Runoff events contributed to 63% of the total sediment load, whereas particulate and dissolved loads in events accounted for between 38–61 and 27–49%, respectively. Runoff events were characterized by high variability in sediment and metal loads, a few events representing a high percentage of the metal exported. Sediment loads were related to maximum and initial discharge. Particulate metal loads were highly correlated with sediment loads, runoff being the hydrological variable that best explains the load of these metals. Dissolved metal loads displayed different patterns. Dissolved Al, showed a great correlation with runoff, while dissolved Mn with maximum discharge.

Metal loads were determined from water samples collected under different streamflow conditions (baseflow and storm events) in a rural catchment (NW Spain) during 4 years. A study at annual, seasonal and storm-event scales was carried out. In all analysed scales, the export order was Fe > Al > Mn > Zn > Cu. A high inter-annual, seasonal and storm-event scale variability of metal load was observed. The total metal loads in stream were higher during baseflow conditions than during storm events, which only represented 4% of the duration of the study period and 25% of streamflow. During storm events, both Al and Fe loads accounted 45% of the total load of the study period, whereas Mn, Cu and Zn loads represented 42%, 33% and 24%, respectively. This highlights the role of high flows on metal export. Only four big events exported around 30% of load of each metal transported in events. At all time scales, a prevalence of export of particulate metals over dissolved metals was observed, more pronounced for Al, Fe and Mn than for Cu and Zn. The export of metals in the Corbeira catchment is influenced by runoff and, to a lesser extent, by the rainfall amount. Copyright © 2014 John Wiley & Sons, Ltd.

Headwater stream, draining from a rural catchment in NW Spain, was sampled during baseflow and storm-event conditions to investigate the temporal variability in dissolved and particulate Al, Fe, Mn, Cu and Zn concentrations and the role of discharge (Q), pH, dissolved organic carbon (DOC) and suspended sediment (SS) in the transport of dissolved and particulate metals. Under baseflow and storm-event conditions, concentrations of the five metals were highly variable. The results of this study reveal that all metal concentrations are correlated with SS. DOC and SS appeared to influence both the metal concentrations and the partitioning of metals between dissolved and particulate. The SS was a good predictor of particulate metal levels. Distribution coefficients (KD) were similar between metals (4.72–6.55) and did not change significantly as a function of discharge regime. Stepwise multiple linear regression analysis reveals that the most important variable to explain storm-event KD for Al and Fe is DOC. The positive relationships found between metals, in each fraction, indicate that these elements mainly come from the same source. Metal concentrations in the stream were relatively low.

Natural fluvial sediments are predominantly composed of river transported debris resulting from weathering and erosion of the basin. Understanding both the concentration and the distribution of metals in the river bed sediments in headwaters is essential to provide a scientific reference for the protection of water resources and the control of water pollution downstream. Sequential chemical fractionation studies of elements in various phases in the environment are widely used in investigating the effects of a particular element in the ecosystem. In this study, determination of aluminum (Al) bound to six phases operationally defined (soluble/exchangeable/specifically adsorbed, bound to manganese oxides, associated with amorphous compounds, bound to oxidizable organic matter, associated with crystalline iron oxides, and residual fraction) in the river bed sediment samples was performed in order to evaluate its potential environmental availability in the monitoring area. Aluminum contents were determined by flame atomic absorption spectrophotometry. The pattern of fractionation of Al in the sediments that are studied suggests that this element does not pose a risk to the aquatic environment under the current environmental conditions since it is mainly part of the potentially less bioavailable geochemical fractions.

This work examined P loss from a mixed land use catchment in northwest Spain and how it was related to hydrological factors. A stream draining a mixed land use catchment of 16 km in northwest Spain was monitored for 5 yr. Water samples were taken more frequently with increased stream flows. A total of 132 runoff events of different magnitudes were analyzed in this study. Mean annual P loss from the catchment was 11.5 kg km, about 68% being transported during runoff events, which only contributed to 29% of the flow. The contribution of runoff events to particulate P and dissolved P losses was 76 and 46% of total losses during the study period, respectively. A high interannual variability in P loss was observed, the differences being related to rainfall amount and distribution. At a seasonal scale, the highest P loads and concentrations were observed during rainy seasons; the lowest P loads occurred in summer because they occurred with stream flow. Particulate P accounted for the greatest proportion (74%) of transported P. There was a high variability in P transported between runoff events, with maximum discharge and discharge increase being the most important variables explaining total P concentration in these events through their effect on suspended sediment concentration.

This paper presents the results of an integrated study that considered the relationship between erosion and stream sediment yield in an agroforestry catchment (16 km2) in NW Spain. The study combined measurements of soil erosion by concentrated flow at field scale with sediment yield measured at the catchment outlet during winter 2007/08. The results indicate that concentrated flow erosion, i.e., rills and ephemeral gullies, occurred on unprotected crop fields. Erosion by concentrated flow was highly discontinuous within the catchment, both spatially and temporally. Soil loss differed significantly from event to event. About 68% of soil loss took place in a single event with a sediment yield of 8.5 Mg, i.e., about 30% of the winter sediment load. Soil losses measured at the Corbeira catchment outlet (28.53 Mg) were indeed more than 5 times lower than those measured on the fields (140.5 Mg of rills and ephemeral gullies and 15.6 Mg for estimated interrill erosion) due to sediment deposition along the route from field to catchment outlet. The sediment delivery ratio was 22%. This value is relatively low due to the presence of abundant vegetation-induced sediment deposition. Sediment delivery to the catchment outlet was determined to a great extent by the spatial distribution of land use, as well as by the poor connectivity between erosion areas and the stream. This catchment is characterized by mosaic vegetation with the grasslands located at the bottom of cropped fields, making sediment delivery to the stream difficult. The results of this study suggest that in the Corbeira catchment soil loss cannot be estimated from the sum of individual field soil losses. Our observations reveal that soil erosion rates measured at one scale are not representative of sediment yield at another scale level.

Using data collected at the Mero catchment during three hydrological years (2005/06–2007/08), an analysis of rainfall–runoff relationships was performed at annual, seasonal, monthly, and event scales. At annual scale, the catchment showed low runoff coefficients (23–35%), due to high water storage capacity soils as well as high runoff inter-annual variability. Rainfall variability was the main responsible for the differences in the inter-annual runoff. At seasonal and monthly scales, there was no simple relationship between rainfall and runoff. Seasonal dynamics of rainfall and potential evapotranspiration in conjunction with different rainfall distribution during the study years could be the key factors explaining the complex relationship between rainfall and runoff at monthly and seasonal scale. At the event scale, the results revealed that the hydrological response was highly dependent on initial conditions and, to a lesser extent, on rainfall amount. The shapes of the different hydrographs, regardless of the magnitude, presented similar characteristics: a moderate rise and a prolonged recession, suggesting that subsurface flow was the dominant process in direct runoff. Moreover, all rainfall–runoff events had a higher proportion of baseflow than of direct runoff. A cluster-type analysis discriminated three types of events differentiated mainly by rainfall amount and antecedent rainfall conditions. The study highlights the role of the antecedent rainfall and the need for caution in extrapolating relationships between rainfall amount and hydrological response of the catchment. Copyright © 2013 John Wiley & Sons, Ltd.

Summary In this study the water draining from a mixed land use catchment of 16 km 2 in NW Spain was monitored over a 5-year period (2004/2005–2008/2009) to determine the temporal variability in phosphorus (P) transport, to examine the P fluxes and controlling factors, and to analyse the relationships between discharge and P (PP: particulate phosphorus and DP: dissolved phosphorus) at event scale. A total of 132 runoff events was analysed, providing an extensive dataset on P values under different hydrological conditions. Mean annual P export from the catchment amounted to 184 kg equivalent to 11.5 kg km −2 , a value relatively lower than those obtained in other mixed land use catchment. The PP accounted for 74% of the total phosphorus (TP). The intra- and inter-annual variability in P transport was high due to the fact that most of P was discharged during a short-time period: 35% of PP load and 19% of DP load occurred in only 2% of the time. Runoff events contributed to 68% of P exported during the period of study. A high variability in P transport during different runoff events was observed. Phosphorus export increased with the magnitude of runoff events and rainfall amount, suggesting that these could be the key factors controlling P yield. Erosion was also an important driving force behind P export in the catchment. The relationships between PP and DP and discharge resulted in different hysteresis patterns. The relationship PP-discharge was mainly characterised by clockwise behaviour, linked to sediment in the surface runoff, while DP-discharge was predominately anticlockwise due to transport in subsurface flow, showing different pathways of transport between PP and DP.

In this study the temporal variability of nitrogen (N) transport in a small rural agroforestry catchment (16 km2) located in NW Spain is analyzed. Total annual N loss was 20.34 t, and the specific N yield was 8.16 kg ha−1 y−1. This rate is low in relation to rural catchments in other regions with similar size and distribution of land use. Nitrate (N-NO3), which represents about 78% of the N transported, was mainly mobilized during baseflow (59%), whereas most of the total Kjeldahl nitrogen (TKN) export occurred during runoff events (54%). A significant difference in the transport of N-NO3 and TKN within the catchment was observed. The relationship between N-NO3 concentrations and discharge within runoff events was mainly dominated by anticlockwise hysteresis loops, whereas in the case of TKN clockwise hysteresis loops predominated.

This work describes the influence of soil use on the evolution of nutrients [ammonium (NH4), nitrate (NO3), nitrite (NO2), phosphate (PO4) phosphorus (P)] and major ions [calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), silicon (Si), chloride (Cl), sulfate (SO4)] concentrations in drainage water of a catchment with two consecutive land uses: first agricultural and then forest. This is a small catchment with previous agricultural diffuse and accidental pollution mainly due to the spreading of slurry. Ion concentrations were monitored over a period of approximately 6 years at the catchment outlet. Agricultural land use was replaced by eucalyptus plantations from mid-July 1998. Great temporal variability was observed for each ion and also among ions. The mean concentrations of studied ions were greatest during the agricultural period. The most pronounced differences occurred for NH4, PO4-P, NO2, and K. All presented the greatest concentration peaks in the agricultural phase, with the exception of Ca...

This article examines the impact of antecedent hydrologic conditions on runoff response and phosphorus (P) export for 132 events measured over a 5-year period (2004/05–2008/09). The study was conducted in the Corbeira catchment, a small agroforestry catchment (16 km2) located in NW Spain, under temperate humid climate. Phosphorus export response to antecedent flow conditions is complex and nonlinear, making it difficult to predict patterns of P export using linear relationships. It has been shown that other factors such as erosion on cultivated land as well as the timing of mineral fertilizer and manure applications play important roles in the P export in this catchment. This work also demonstrates the need to examine larger data sets when the relationships between hydrologic conditions and P export are analyzed to capture the high variability shown in these types of catchments.

This study aims to determine aluminum fractions in the fine earth of acidic soils under different land uses (forest, pasture and cultivation) and in the river bed sediments of the headwater of the Mero River in order to identify and quantify Al-bearing phases to assess Al mobility and potential bioavailability (environmental availability) in the monitoring area. Sequential extraction is used to evaluate the Al partitioning into six fractions operationally defined: soluble/exchangeable/specifically adsorbed, bound to manganese oxides, associated with amorphous compounds, aluminum bound to oxidizable organic matter, associated with crystalline iron oxides, and residual fraction (aluminum within the crystal lattices of minerals). The mean concentration of total aluminum (24.01 g kg-1) was similar for the three considered uses. The mean percentage of the aluminum fractions, both in soils and sediments, showed the following order: residual fraction ≫ amorphous compounds ≈ crystalline iron oxides > water-soluble/exchangeable/specifically adsorbed > bound to oxidizable organic matter ≈ Mn oxides. However, in the soils, the amorphous compounds and water-soluble/exchangeable/specifically adsorbed fraction showed considerable differences between some types of uses, the percentage of aluminum linked to amorphous compounds being higher in forest soils (16% of total Al) compared to other uses (mean about 8% of total Al). The highest values of water-soluble/exchangeable/specifically adsorbed Al were also found in forest soils (mean 8.6% of the total Al versus about 4% of pasture and cultivation), which is consistent with the lower pH and higher organic matter content in forest soils. Nevertheless, the potentially bioavailable fraction (sum of the first three fractions) is low, suggesting very low geoavailability of this element in both soils and sediments; hence, the possibility to affect the crops and water quality is minimal.

[Abstract] Soil losses and the subsequent sediment delivery constitute significant environmental threats. Climate change is likely to have an impact on the availability of water and therefore on sediment yield in catchments. In this context, quantifying the sediment response to an increased atmospheric CO2 concentration and climate change is of utmost importance to the proper management of rural catchments. However, quantitative assessment of climate change impact remains a complex task. In this study, the potential medium (2031–2060) and long-term (2069–2098) impacts of projected changes of temperature, rainfall and CO2 concentration on sediment yield in a small rural catchment located in NW Spain were evaluated using the Soil and Water Assessment Tool (SWAT) model. Climate change scenarios were created using future climate data projected by regional climate models from the ENSEMBLES project and two CO2 concentration scenarios (550 and 660 ppm). The results showed that climate change would have a noticeable impact on suspended sediment if the forecast temperature, rainfall and CO2 concentration changes included in this study were met. Overall, suspended sediment is expected to decrease (2031–2060: −11%, 2069–2098: −8%) compared to the baseline period (1981–2010), mainly due to decreased streamflow. However, an increase in sediment transport in winter is predicted, possibly associated with increased erosion in cultivated areas (11%–17%), suggesting that, at this time of the year, the effect of soil detachment prevails over sediment transport capacity. Consequently, management practices aimed at reducing soil erosion in cultivated areas should be carried out, because these are the main source of sediment in the study area. Galicia. Consellería de Economía e Industria; 10MDS103031 Ministerio de Economía y Competitividad; CGL2014-56907-R

Suspended sediment and sediment-bound pollutants deteriorate the ecological status of many freshwater bodies around the world. Maintaining and restoring the ecological status require planning strategies that strongly rely on integrated basin models that correctly identify the main sources of sediment within the catchment and quantify the sediment yield. This study assesses the applicability of the SWAT (Soil and Water Assessment Tool) model to simulate sediment yield in a small (16-km2) rural catchment (Corbeira) in northwest Spain and determines the contribution of different land uses to sediment export at the catchment outlet. The SWAT model was calibrated and validated for monthly sediment yield using measured sediment yield data obtained at the catchment outlet from 2005 to 2010. The results showed good agreement between measured and simulated monthly sediment values (R2 values of 0.67 and 0.84, percent bias values of 6% and 12%, and Nash-Sutcliffe efficiency values of 0.48 and 0.50 during the calibration and validation periods, respectively), indicating that SWAT is a useful tool for simulating sediment yield under the conditions prevailing in the Corbeira catchment. Therefore, the validated model can be used to evaluate the influence of alternate soil management practices in controlling erosion and sediment yield in this catchment. Cultivated lands (4% of total catchment area) were the largest contributors (79%) of sediment yield in the study area, where the soil formation rate for conditions prevailing in Europe was slightly exceeded.

Geochemical processes related to dissolved organic carbon (DOC) under baseflow are studied in Corbeira Stream (northwestern Spain). The stream drains a catchment occupied by forest and agricultural fields. Dissolved organic carbon and other chemical parameters were analyzed. Seasonally, DOC values show a gradual rising background beginning in late spring to summer, finishing with major anomalies in the early to middle autumn. Suspended solids (SS) values exhibit a steady to falling background. The greatest DOC peaks seem be a function of rising temperatures and degradation of organic matter in wet soils. Divergent DOC and SS backgrounds in dry season and synchronicity between DOC-SS peaks associated with negative correlation of SS to pH in autumn seem be conspicuous geochemical signatures in perennial streams under temperate climates. The first one indicates the predominance of subsurface flows in streams, and the second one indicates the predominance of overland runoff.

The hydrological response of a small agroforestry catchment in northwest Spain (Corbeira catchment, 16 km2) is analysed, with particular focus on rainfall events. Fifty-four rainfall–runoff events, from December 2004 to September 2007, were used to analyse the principal hydrological patterns and show which factors best explain the hydrological response. The nonlinearity between rainfall and runoff showed that the variability in the hydrological response of the catchment was linked to the seasonal dynamics of the rainfall and, to a lesser extent, to evapotranspiration. The runoff coefficient, estimated as the ratio between direct runoff and rainfall volume, on an event basis, was analysed as a function of rainfall characteristics (amount and intensity) and the initial catchment state conditions prior to an event, such as pre-event baseflow and antecedent rainfall index. The results revealed that the hydrological response depends both on the soil humidity conditions at the start of the event and on...

Major cations [calcium (Ca), magnesium (Mg), sodium (Na), potassium (K)], anions [nitrite (NO2), nitrate (NO3), choride (Cl), sulfate (SO4)], dissolved copper (Cu) and zinc (Zn), total nitrogen (TN), dissolved phosphorous (DP), total phosphorus (TP), suspended solids (SS), chemical oxygen demand (COD), dissolved organic carbon (DOC), and O2 were analyzed in a small stream draining an agroforestry catchment located in northwest Spain. The mean concentrations found were relatively low compared to global “average” values. The results are consistent with the low population density and the nonintensive agriculture developed in the catchment. The nutrient balance offers relatively low loss rates for nitrogen (N) and phosphorus (P) (14.6% and 1.8%, respectively), although losses could have been underestimated by the use of regular sampling. Moreover, soil analysis reveals a possible P accumulation in cultivated fields of the catchment. Correlation analysis shows that components with a greater presence in fertili...

Data on dissolved copper (Cu), zinc (Zn), manganese (Mn), iron (Fe), and aluminum (Al) are presented for surface waters from an agricultural catchment transformed into forest in northwest Spain. The use and management types carried out in the catchment were as follows: agricultural catchment with spreading of slurries using a conventional tank, agricultural catchment with intensive slurry application, and reforested catchment without slurry application. Concentrations of the metals in the runoff ranged widely (Al, 18–204; Fe, 7–374.5; Mn, 1.5–680; Cu, 0.29–121.6; Zn, 2.8–164.3 μg L–1). The mean concentrations of studied metals were greatest in the agricultural period. They all present the greatest concentration peaks in the agricultural catchment phase with massive slurry application. This period especially affected the concentrations of dissolved Cu and Mn, as well as those of Zn and to a lesser extent those of Al and Fe. Temporal variations in trace elements at the catchment outlet suggest that dissolve...

This study focuses on the role of runoff events in influencing concentrations and export of suspended sediments and phosphorus in a headwater stream draining an agroforestry catchment in northwestern Spain. Large differences exist between suspended sediment and phosphorus (P) concentrations measured during base-flow conditions and runoff events, with a higher delivery during runoff events. Suspended sediment and phosphorus exports were 29.44 and 0.08 kg ha−1 y−1 respectively, with more than 50% delivered during runoff events (12% of the year). The relative contributions of phosphorus forms to the total annual export were 75% and 25% as particulate and dissolved phosphorus, respectively. Soil erosion is the main source of suspended sediment and phosphorus in the stream.

This article examines the metal [aluminum (Al), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn)] runoff dynamics in the Mero River (northwestern Spain). At the catchment outlet, metal concentrations, suspended solids, dissolved organic carbon, pH, and discharge were determined during three runoff events. The river drains an agroforestry catchment of 65 km2 with relatively high livestock density. Dissolved and particulate metal concentrations increased during the events with respect to pre-event concentrations, but the increase of the dissolved fraction is relatively small compared to that of the particulate fraction. The dissolved metal concentration peaks appeared after the hydrograph peak, suggesting transport associated with subsurface flow. For particulate metals, peaks usually occurred during the falling limb of hydrograph, implying distant-river source of metals. Particulate forms represented more than 90% of total Al, Fe, and Mn load, whereas for Cu and Zn its contributions were 52–76% and 31...

This paper presents preliminary results from an analysis of hydrological variability of a catchment located in Galicia (NW Spain), with particular focus on the effects of climate variability (temperature and precipitation), using daily streamflow data for the period October 2004 to September 2009. The climate variability has been studied by means of data obtained in a meteorological station on the area. The analysis is based on the examination of statistical parameters, flow duration characteristics, baseflow separation and the relationship between measured streamflow and precipitation. The results show that daily, monthly and annual streamflow are highly variable in this catchment. At seasonal scale about 65% of the water flows in winter (33%) and spring (32%) months, although with significant differences between years. This seasonality essentially relates to distribution and characteristics of precipitation episodes. However, there is not a narrow relationship between precipitation and streamflow, because soil moisture conditions have an important role in the hydrological behaviour of the catchment. The baseflow contribution to total streamflow is quite high, with baseflow index values above 0.69, which is consistent with the characteristics of the study area, such as geology (dominated by schist), soils (Umbrisols and Cambisols), vegetation cover (over 65% forest area) and precipitation characteristics (heavy, long duration and low intensity). The flow duration analysis also reveals that the flow regime is dominated by baseflow, recording high flow peaks during a limited period of the year. The study reveals that the major cause of streamflow variability in this catchment is related to precipitation distribution and soil moisture conditions. The results suggest that the Corbeira stream undergoes a reduction in low streamflows and an increase in the frequency of high flows, hence producing an increase in the risks associated with these changes.

Catchment scale suspended sediment (SS) transport studies in northwest Spain are of special interest as little research at this scale has been done in this region. However, the role of sediments in the transfer of nutrients and contaminants to coastal areas in this region has been highlighted. Data were collected from the Corbeira catchment during a 3-year period and the variability in SS load at different temporal scales (within-events variability, monthly/seasonal, and annual) was analyzed. The statistical relationship between discharge and suspended sediment concentration (SSC) from samples obtained every 15 days as well as during runoff events in October 2004 to September 2007 showed a marked scatter of points. Hence, the rating curve method does not seem appropriate to estimate SSC in this catchment. The results also demonstrated that at the within-events scale, most of the SS peaks preceded the discharge peaks (70% of runoff events), implying that zones nearby or well connected to the stream are the dominant sediment source areas. In some cases, rills and ephemeral gullies developed in cropland were the main source of sediment delivered to the stream. Furthermore, a reduction in SSC was observed in sequences of events, which can be mainly linked to a phenomenon of sediment exhaustion. At the seasonal scale, most of the total annual SS load was transported during the autumn months, the period in which, generally, the largest number of events occurred, while in the summer, total annual SS load was very low

A study was carried out on a rural catchment located in northwest Spain to examine the sediment yield from the catchment by measuring suspended sediments during rainfall events. Within the catchment regular surveys were conducted to obtain data on the suspended sediment sources. Important variations in sediment load were detected at event scale (0·3–21·0 Mg); some of these can be explained in terms of event size, antecedent conditions, rainfall distribution and soil surface erosion. To study the variables controlling suspended sediment yield during the events in the catchment, several event and pre-event variables were calculated for all events. The sediment load is strongly influenced by discharge variables. During the events discharge–suspended sediments were also analysed. When the soil surface was unprotected, the formation of rills and ephemeral gullies on agricultural land at the catchment head was an important source of suspended sediments in the catchment. Copyright © 2010 John Wiley & Sons, Ltd.

This study was conducted to evaluate the factors controlling sediment and phosphorus export in a small agroforestry catchment located in NW Spain. At the catchment outlet discharge was continuously measured and suspended sediment (SS) and total (PT), particulate phosphorus (PP) and dissolved phosphorus (DP) were determined during seven rainfall events occurred in autumn. Sediment and sediment-associated P export differed significantly between events. Particulate P was a greater portion of P transported in runoff. A large proportion of SS and PP exported from the catchment occurred from a relatively small portion of the catchment and during only two events. Rills and gullies delivered most of the eroded sediment directly to the stream, which contribute to high sediment and phosphorus exportation at the catchment outlet. Strong correlations between P and SS concentrations suggest that erosion processes are important in P fluxes. The highly significant correlation between SS and P concentrations in the stream enables to estimate transported P using SS in the Corbeira catchment. Copyright © 2009 John Wiley & Sons, Ltd.

This article reports the contribution of four rain events to the metal load [aluminum (Al), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn)] reaching a small stream draining an agroforestry catchment in northwestern Spain. During events and at base flow, the mean total metal contents present in the following order of abundance: Fe > Al > Mn > Zn > Cu. In general, the mean total metal concentrations in the stream were always higher during the rain events than during base flow. The contribution of dissolved metals to the total metal concentrations during events was less than 10% for Al, Fe, and Mn, whereas for Cu, and especially for Zn, its contribution was much higher and for Zn exceeded 50% in some events. Particulate fractions of Al, Mn, and Fe during rainfall events showed significant positive correlations with flow rate and suspended solids. Overall, it can be concluded that the amounts of Al, Fe, and Mn reaching the stream during rainfall events were related to the amount of soil erosion occurri...

Patterns of phosphorus (P; dissolved and particulate) and nitrate (NO3) delivery were compared between times of base flow and events in a stream draining a small agroforestry catchment in Galicia, northwest Spain. Nutrient concentrations were low during base flow, and only nitrate shows a clear seasonal pattern. In general, particulate phosphorus (PP) was the dominant fraction of the total P. Particulate P concentrations increased significantly during storms, with maximum concentrations occurring on the rising limb of the hydrograph (clockwise hysteresis). The rapid response of PP suggests a near‐stream source of PP during events. The surface runoff is the mainly route to transport PP to the stream, whereas for the dissolved phosphorus (DP) and NO3 the subsurface path is also important.

The construction of a large reservoir on the Parana River (Selviria, MS, Brazil) disturbed the soil of an extensive agricultural area in which between 5 and 8 m of topsoil were removed. In this area, a restoration process was carried out using revegetation with green manure without or with amendments (for 4 years), crops (2 years), and Brachiaria decumbens cultivation for 6 years. The following treatments were used: control plots, T0 (residual subsoil) and T1 (soil tillage without culture); plots with green manure and without amendments: T2 (velvet bean) and T3 (pigeon pea); plots with green manure and with amendments: T4 (limed + velvet bean), T5 (limed + pigeon pea); T6 (limed + gypsum + velvet bean) and T7 (limed + gypsum + pigeon‐pea). They were arranged in randomized blocks. After 13 years of rehabilitation process, when the soil was cultivated with brachiaria, the structural stability in three depths was evaluated. Organic‐matter content and others chemical properties did not show any relationship w...