E. Álvarez

Heavy metals in the dump of an abandoned mine in Galicia (NW Spain) and in the spontaneously occurring vegetation.

The concentrations of different forms of heavy metals (Fe, Mn, Zn, Cu, Cr, Ni, Cd and Pb) were determined in a mine dump material rich in chalcopyrite. The concentrations were compared with those of the natural vegetation colonising the dump. Samples taken from the dump are acid (pH(H(2)O) between 3.0 and 5.0), have carbon contents lower than 0.5%, N lower than 0.2%, effective cation exchange capacity between 0.74 and 4.96 cmol(+)kg(-1) and percent Al saturation in the exchange complex higher than 20% in 85% of the samples. Iron was the most abundant heavy metal, in both total and bioavailable forms, and the relative abundance of metals was: Fe>Cu>Mn>Zn>Cr. The total Fe concentrations ranged between 4315 and 31578 mg x kg(-1), the total Cu between 273 and 5241 mg x kg(-1), the total Mn between 294 and 2105 mg x kg(-1), the total Zn between 73 and 894 mg x kg(-1) and total Cr between 0.01 and 30 mg x kg(-1). Ni, Cd and Pb were below the analytical detection limits. The concentration of bioavailable Fe ranged between 40 and 1550 mg x kg(-1); Zn was the least abundant metal in this fraction (between 2 and 100 mg x kg(-1)). Copper was the most abundant heavy metal in the exchange complex and in the aqueous extracts, followed by Zn, Mn and Fe. Exchangeable Cu ranged between 17.7 and 1866 mg x kg(-1), whereas the maximum concentrations of exchangeable Zn, Mn and Fe did not exceed 140 mg x kg(-1). The Cu concentration in the aqueous extracts varied between 0.1 and 8.3 mg x l(-1) and the concentration of Fe was always less than 0.52 mg x l(-1). The heavy metal contents in the spontaneously occurring vegetation in the dump ranged between: 150 and 900 mg Fe x kg(-1), 84 and 2069 mg Mn x kg(-1), 20.5 and 106 mg Cu x kg(-1) and between 35 and 717 mg Zn x kg(-1), when considering all the plant samples analysed. Festuca sp. accumulated Fe, Salix atrocinerea accumulated Zn and Mn, and Frangula alnus and Quercus robur accumulated Mn. These native plant species may contribute to decrease the heavy metal contents in the dump material.

Dynamics of glyphosate and aminomethylphosphonic acid in a forest soil in Galicia, north-west Spain

Residues of the herbicide glyphosate (N-phosphonomethylglicine) and its main metabolite, aminomethylphosphonic acid (AMPA), were determined in a forest soil in north-west Spain, previously treated with 5 and 8 l ha(-1) of glyphosate. Both products were monitored in the solid and liquid soil phases for an 8-week period after the treatment. Soil samples were extracted by KH2PO4. Concentrated extracts and liquid phase samples were derivatized with 9-fluorenylmethyl chloroformate (FMOC) before determination by HPLC using an anion exchange column and spectrofluorometric detection. The treated soil peaked at 6.9 microg g(-1) of glyphosate, whereas soil water samples peaked at 0.74 microg ml(-1) of glyphosate. One month after the treatment, both glyphosate and AMPA concentrations in soil and water samples were almost negligible. AMPA peaked at 0.77 microg ml(-1) in soil water samples. Glyphosate and AMPA exhibited high vertical mobility in the treated soil, quickly reaching high concentrations in subsurface horizons where the degradation is slower.

Aluminium fractionation in Galician (NW Spain) forest soils as related to vegetation and parent material

Aluminium extracted by acid oxalate, pyrophosphate, CuCl2 and NH4Cl, as well as concentration and speciation of aluminium in the soil solution, were studied in soils from the province of Lugo (Galicia, Spain). Soils, developed from different parent materials (granodiorite, shale and limestone), differ also in type of vegetation (oak (Quercus robur), pine (Pinus radiata) and eucalypt (Eucalyptus nitens)) and degree of evolution. Soils developed from limestone, highly developed and acid, showed the highest contents of all forms of non-crystalline and organically bound aluminium. The tree species affected significantly the contents of the most labile aluminium forms (exchange and solution aluminium), which were highest in soils developed from limestone and bearing pine vegetation.

Evaluation of Mehlich 3 reagent as a multielement extractant in mine soils

The usefulness of Mehlich 3 (M3) reagent was evaluated as a method to extract numerous elements from coalmine soils in As Pontes (Spain) showing a wide range of physicochemical properties. Critical levels (deficiency and/or toxicity) were established for plant available elements extracted by this reagent. The M3 method was compared to 1M NH4Cl, Olsen, acid oxalate, and DTPA methods as extractants for exchangeable Ca, Mg and K, available P, non-crystalline aluminium, and available heavy metals, respectively. The M3 method correlated significantly to NH4Cl for Ca, Mg and K (r=0·76, 0·84 and 0·87, respectively), to Olsen P (r=0·77) and to oxalate Al (r=0·77). Significant correlations were found between Fe, Cu, Zn and Cd extracted by M3 and DTPA; for Mn, Ni, Co and Pb different relationship between methods were obtained for acid and alkaline samples, so that critical levels were established for M3 metals as a function of soil pH. Copyright

Speciation and solubility control of Al and Fe in minesoil solutions

Abstract Solutions obtained from minesoils originating from the opencast lignite mine dump at As Pontes (Galicia, NW Spain) were studied. Spoils were very heterogeneous and there were a wide range of environments. Generally, solutions showed high electrical conductivity, often with large quantity of weathering products derived from pyrite oxidation (Fe, SO 4 2− , H + ), as well as Al and Si originating from mineral alteration. The Al fractioning showed (a) in the most acid areas (pH 4 was the dominant complexeand Al 3+ was the second most common; (b) at pH values between 5.0 and 6.0, AlF monomers were the most abundant complexes; (c) at pH values > 6.0, AlOH species were most common. The distribution of Fe species was chiefly determined by the EhpH conditions and SO 4 2− contentss in the solution. Generally, in areas with a pH 600 mV, Fe was found as FeSO 4 complexes, while in areas with a pH > 6.0 the only species present were Fe-hydroxy-monomers. The Al 3+ activity in soil solution seems to be controlled by a jurbanite-type mineral at pH 3 seems to exercise this control at pH > 5.0. With regards to Fe, in the most acid (pH 4 ·7H 2 O being the mineral phase closest to the equilibrium.

Use of Mussel Shells as a Soil Amendment: Effects on Bulk and Rhizosphere Soil and Pasture Production

Abstract Large quantities of mussel shells (66 000–94 000 t year −1 ), an alkaline material that can be used as a soil amendment, are generated as waste in Galicia, NW Spain. A field trial was carried out by planting different pasture species in a Haplic Umbrisol using a randomized block design with four blocks and six treatments (not amended control or soil amended with lime, finely ground shell, coarsely ground shell, finely ground calcined shell or coarsely ground calcined shell) to compare the effects of lime and mussel shells additions on a soil with a low cation exchange capacity and high Al saturation. The trial was established in March 2007, and samples of plants and soil were collected when plots were harvested in summer 2008 (separating the bulk and rhizosphere soil). The soils were analyzed for pH, total C, total N, available P, exchangeable cations, effective cation exchange capacity and available micronutrients. Dry matter yield was measured in all plots and plants were analyzed for nutrients. Application of mussel shells and the commercial lime resulted in an increase in pH and exchangeable Ca and a decrease in exchangeable Al and Al saturation. The stability of pH over time was high. These effects were most noticeable in the rhizosphere. The amendment also had a positive effect on dry matter yield and concentration of Ca in the plant.

Fluorine sorption by soils developed from various parent materials in Galicia (NW Spain)

Fluorine is a phytotoxic element that can reach the soil from various industrial activities. Fluorine sorption by soil is crucial to protect water and food chain from fluorine pollution. In Galicia (NW Spain), various activities emit fluorine into the atmosphere, mainly ceramic industries and an aluminium smelter. This study, aiming to investigate fluorine sorption by Galician soils, was conducted on natural soil horizons representative of the area. Most soils were acid and rich in organic matter and showed strong fluorine sorption. The lowest sorptions were exhibited by a near-neutral serpentinite-derived soil (1001 mg kg(-1)) and the B horizons of soils developed from quartz schist (989 mg kg(-1)), and the highest by the A horizons of amphibolite-derived soils (1783 mg kg(-1)). In soils developed from quartz schist, biotitic schist and amphibolite, A horizons sorbed more fluoride than the corresponding B horizons (average 1621 and 1324 mg kg(-1), respectively), while the opposite is true in granite-derived soils (average 1644 and 1324 mg kg(-1), respectively). In the A horizons, the F sorption significantly correlated to soil pH (r=-0.79), pH in NaF (r=0.83) and oxalate Al (r=0.81). In the B horizons, sorption correlated to soil pH (r=-0.78), oxalate Fe (r=0.71) and organic C (r=0.66). F sorption can be described by both the Langmuir and Freundlich equations. The concentration of free fluoride in the equilibrium solutions increased above pH 6.

Rhizosphere chemistry in acid forest soils that differ in their degree of Al-saturation of organic matter

&NA; The objective of this research was to study the rhizosphere of tree species of acid forest soils derived from amphibolite (AMP) and granite (GR) rocks, so that the influence of the type of pedogenesis (generated by these materials) on its chemistry could be established. Umbric A1 horizons were sampled in three AMP soils (Lithic Hapludands, Andic Dystrudept), under oak, pine, and eucalyptus stands, and in three nearby GR soils (Typic Dystrudepts) under identical stands. The A1 GR horizons had a lower pH (4.2 vs 4.6), and greater aqueous soluble Al (0.40 vs 0.06 mmol kg−1) and NH4Cl‐extractable Al contents (6.8 vs 2.6 cmolc kg−1) than the A1 AMP horizons. Mean values of sodium pyrophosphate extractable‐Al (Alp) and ammonium oxalate extractable‐Al (Alo) in the A1 AMP horizons were 12.0 and 16.2 g kg−1, respectively, and the molar ratio between Alp and sodium pyrophosphate extractable‐C (Cp) ranged between 0.1 and 0.2. Mean values of Alp, Alo, and Alp/Cp in the A1 GR horizons were significantly (P < 0.05) smaller (5.2 g kg−1, 5.3 g kg−1, and 0.06, respectively). In the A1 GR horizons, we observed a lower pH (significant at P < 0.05) in the rhizosphere than in the bulk soils, a pattern which was not observed in the A1 AMP horizons. The balance of nutritive cations and anions between rhizosphere and bulk soils did not explain the patterns of pH change. Based on the relationships found among organic acids, soil pH, and Alp/Cp, we propose that, in the A1 GR horizons, where organic matter is Al‐undersaturated, the increased organic acidity produced in the rhizosphere cannot be completely buffered by Al alkalinity, whereas in the AMP soils, where mineral amorphous Al coexists with Al‐humus complexes, organic compounds become stabilized with reactive Al surfaces, maintaining organic acidity at low levels, even in the rhizosphere (whenever the stabilization capacity of these surfaces is not exceeded). Our results imply that both variations in organic matter content and the degree of metal saturation of the organic matter need to be considered when investigating the causes behind changes in soil pH in the rhizosphere of acid forest soils.

Limestone particle size and liming scheduling influence soil properties and pasture production.

Liming is a common practice in Galician (NW Spain) soils devoted to pasture production. Although many studies have established the right liming rates, there is a lack of information concerning the ideal particle size for optimal agronomic results. This study aims to evaluate the effects of particle size (2-4, 0.5-2, 0.25-0.5, <0.25 mm) of magnesium limestone as well as the application schedule (in a single application or split in 3 yearly applications) on the proprieties of an acid soil in Galicia and on the yield and quality of pasture growing on the soil during the 2 years after liming. The soil proprieties were monitored seasonally, and the pasture yield and nutritional contents were determined in summer and autumn. The soil analysis showed that the plots treated with a single application of the finest limestone exhibited the highest pH (pH water 5.05-5.53), and the lowest exchangeable Al (<10% Al saturation throughout the period of study), the highest concentrations of exchangeable Ca (8.40-10.18 cmol(+) kg−1) and Mg (1.39-1.71 cmol(+) kg−1) and the highest effective cation exchange capacity (11.2-13.7 cmol(+) kg−1). In contrast, plots treated with the coarsest limestone had values similar to control plots. The highest production of total dry matter and, especially, the highest yield of sown species were found in the plots receiving the finest limestone (0.75-1.10 t ha−1 dry matter in summer harvest versus 0.30-0.75 t ha−1 in control plots). Available P, exchangeable cations (K and Ca), and pH explain a high percentage of the variance of these parameters. The Mg concentrations and the total contents of Ca and Mg in plant tissues were significantly higher in the plots treated with the finest limestone.

Influence of fluoride addition on the composition of solutions in equilibrium with acid soils.

Abstract Atmospheric emissions of fluoride from an aluminium smelter-alumina refinery located on the northern coast of Galicia, NW Spain, increase the content of fluorine in soils and vegetation in the vicinity of the complex. The effects of the addition of fluoride solutions on the chemical properties of soil samples from the area surrounding the complex were investigated in laboratory experiments. Addition of fluoride to soils resulted in increases in pH and concentrations of Fe, Al, and organic matter in the equilibrium solutions and decreases in concentrations of Ca, Mg, and K. No consistent effects were observed on the Cu, Mn, or Zn concentrations. Most of the Al in solution was bound to organic matter. Within the fraction “labile aluminium”, the concentration of Al-OH complexes decreased and the Al-F complexes increased, especially AlF3 and AlF−4, which are less toxic than Al3+ and Al-OH species.