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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.

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...

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.

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.

Partitioning to suspended sediments plays an important role in controlling metal speciation in natural waters. In order to model both dissolved and particulate forms of metals, it is essential to determine possible relationships between partition coefficient (KD) and various water quality variables. This paper examines temporal variability in particulate and dissolved metals (Al, Fe, Mn, Cu, and Zn) collected from a rural stream (NW Spain) during three years under baseflow and runoff events conditions, and investigates the role of pH, suspended sediments (SS) and dissolved organic carbon (DOC) on KD of these metals. The mean concentrations of metals during events were much higher than those in baseflow (except MnD and CuD), but particulate metals were always predominant. Metal concentrations did not exhibit a seasonal pattern. Generally, a similar pattern of metals to discharge was seen for both hydrological conditions, although different metal-discharge relationships were observed depending on the type and form of the metal: negative for FeD and MnD, no relation for AlD, CuD, and ZnD, and positive correlation for all particulate metals (except for CuP and ZnP in baseflow). Partitioning results showed that SS and DOC were the main factors in controlling KD of all metals during events (except for Fe) as well as KD of Al under baseflow. SS play the most important role on KD of Cu and Zn in baseflow, and DOC on KD of Fe (regardless of the discharge regime). For all the above-mentioned findings, this study demonstrates the need to consider hydrological changes when we analyze geochemical factors affecting metal concentrations, even in relatively unpolluted environments.

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.

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.

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...

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

This study discusses the soil surface conditions under which crusting and runoff are generated. A field survey was conducted in three agricultural districts in the province of A Coruña (Galicia, Spain), where the soils, developed over basic schists in a temperate-humid climate, are prone to crusting. A total of 168 freshly tilled surfaces and the cumulative natural rainfall since the last tillage operation were studied. The agricultural situations corresponded to primary and secondary tillage, crop seedbeds and pasture seedbeds. Stages of soil crusting were recorded by visual assessment, based on the estimation of the extent of structural, transitional and sedimentary crusting. The runoff was estimated by measuring the maximum distance reached by soil particles carried by the runoff and then deposited on the soil surface where there were no incisions on soil. Surface crusting was observed in all agricultural situations. The amount of accumulated rainfall required to form a fully sedimentary crust was variable, depending largely on the initial soil surface roughness. On average, 50, 150 and 350 mm of accumulated rainfall were required for soil surfaces with a low, medium and high roughness, respectively. The combination of three soil surface conditions (crusting stage, roughness and vegetation cover) was primarily responsible for the start of runoff formation.

In this study, the water draining a catchment of 65 km2 in NW Spain was monitored over a 3-year period to examine temporal variability of five metal concentrations (Al, Fe, Mn, Cu, and Zn) in dissolved form and also in suspended solids (SS), under two different hydrological conditions—in baseflow and stormflow events. pH, SS and dissolved organic carbon (DOC) were also examined as possible factors affecting metal transport mechanisms. The results showed that AlD, CuD, and ZnD were significantly (p

Concentrations of Al, Fe, Mn, Cu and Zn (dissolved and particulate), suspended sediment, dissolved organic carbon, and pH and discharge were determined during a 3-year period in a stream water of an agroforestry catchment in Galicia (NW Spain). The objective of this study is to investigate the role of these variables in the control of dissolved and particulate concentrations of each metal in the stream water. The soils in the catchment are developed on metamorphic schist. Stream water samples were collected at the catchment outlet every 15 days and more frequently with increased stream flows. Metal concentrations were measured by ICP- MS. Pearson correlation coefficients were calculated to examine the possible associations between metals and the four variables under consideration. Stepwise multiple regressions were applied to determine which predictor variables have the strongest influences on controlling concentrations of each metal in the stream. The results showed that metal concentrations were relatively low (Fe > Al > Mn > Zn > Cu), but particulate metals were predominant over those dissolved. Stepwise multiple regression analysis revealed that the most important variable to explain dissolved concentrations for Al, Fe and Cu was the dissolved organic carbon, whereas the suspended sediment was for dissolved Zn and the discharge was for dissolved Mn. The suspended sediment was also a good predictor of particulate metal levels.