Aluminium geochemistry in the bulk and rhizospheric soil of the species colonising an abandoned copper mine in Galicia (NW Spain)

Abstract

Purpose Aluminium partitioning in the solid fraction and aluminium in solution in the bulk and rhizospheric soil of different plant species colonising an abandoned Cu mine slope (Calluna vulgaris, Erica cinerea and Salix atrocinerea) and mine dump (C. vulgaris and E. cinerea) were investigated. The aim of the study was to determine the changes that the species induce in the Al forms in the rhizosphere in order to adapt to heterogeneous substrates. Materials and methods Al was extracted from the solid phase with different solutions: ammonium oxalate (Alo), sodium pyrophosphate (Alp), copper chloride (Alcu), lanthanum chloride (Alla) and ammonium chloride (AlNH 4 ). The following Al fractions were obtained: inorganic non-crystalline Al (Alop=Alo-Alp), highly stable organoaluminium complexes (Alpcu=Alp-Alcu), organoaluminium complexes of intermediate stability (Alcula= Alcu-Alla) and labile organoaluminium complexes (Alla). The concentration of Al present in the aqueous phase was also determined. Results and discussion The pH of the soil in the mine slope was close to 7, and the roots of Ericaceae caused strong acidification so that the pH of the rhizospheric soil was low (3.6-4.7). In contrast, the pH of the bulk and the rhizospheric soil of S. atrocinerea remained close to 7. In the mine dump (pH3.7), the changes in the pH of the Ericaceae rhizosphere in relation to the bulk soil were not as marked as in the mine slope. Alop predominated in the solid phase (more than 70% of the Alo), and Alpcu predominated in the organoaluminium complexes (more than 55%), followed by Alcula (13% and 47%) and Alla (3% and 21%). The concentration of Al in solution was significantly related to the concentrations of AlNH 4 (r=0.43), Alla (r=0.50) and Alcula (r=0.45). Conclusions Ericaceae species grew in dump and slope materials because they modified the pH of the rhizospheric soil, while S. atrocinerea only grew in areas where the soil conditions were close to neutral. The concentration of aluminium fractions was higher in the Ericaceae rhizosphere soil than in Ericaceae bulk soil, S. atrocinerea rhizosphere and bulk soils. Moreover, highly stable organoaluminium complexes predominated, and the dissolved Al concentration was low, despite the strong acidity.

Influence of parent material on the aluminium fractions in acidic soils under Pinus pinaster in Galicia (NW Spain)

“…The extraction sequence of the different solutions in soils of slate, mica schist and granite was Al p N Al o N Al cu N N Al la N Al NH4 . Higher concentrations of Al p than of Al o have also been found in other Galician soils (Camps Arbestain et al, 2003;Álvarez et al, 2010;Ferro-Vázquez et al, 2014) and in soils with high organic matter content (Berggren and Mulder, 1995;Drabek et al, 2003;García-Rodeja et al, 2004;Walna et al, 2005). The authors attributed this to the predominance of organo-aluminium complexes within non-crystalline Al and the possible extraction of inorganic forms by the pyrophosphate, especially low crystallinity Al(OH) 3 phases and Al of the clay interlayers.…”

“…However, these methods have been verified and used for many years (Urrutia et al, 1995;Fernández-Sanjurjo et al, 2001;Álvarez et al, 1992, 2010Drabek et al, 2003;García-Rodeja et al, 2004, 2007Matús, 2007;Frankowski et al, 2013;Ferro-Vázquez et al, 2014).…”

Efficacy of two different reclamation strategies to improve chemical properties and to reduce Al toxicity in a lignite mine dump during a 20‐year period

“…In plots treated with topsoil, as well as in control plots, IS values for that mineral were lower than 1 in year 2012 (Rivas-Pérez et al, 2016), indicating that the decrease in Al o and Al op values could not be explained by a trend to increase crystallinity but by an increase of Al in solution. Monterroso et al (1994), studying plots with pH > 5 in the same dump, found that Al 3+ activity was controlled by low crystallinity Al (OH) 3 minerals, whereas other authors pointed out that organoaluminum complexes and exchangeable Al controlled Al activity in the soil solution of soils with pH > 4.5 (Álvarez, Fernández-Sanjurjo, Otero, & Macías, 2010;Guo et al, 2006). In the present study, both mechanisms could be taking place, depending on the restoration strategy that was used.…”

Aluminium leaching response to acid precipitation in a lime-affected soil

“…Also, this form can be readily leached. However, if environmental conditions vary, solubilized Al can be reincorporated into the solid phase forming precipitates and/or complexes, or can be bound to exchange sites (Guo et al, 2007;Álvarez et al, 2010).…”