Pedogenesis and nickel biogeochemistry in a typical Albanian ultramafic toposequence

Abstract

This study aimed at relating the variability of Ni biogeochemistry along the ultramafic toposequence to pedogenesis and soil mineralogy. Hypereutric Cambisols dominate upslope; Cambic Vertisols and Fluvic Cambisols occur downslope. The soil mineralogy showed abundance of primary serpentine all over the sequence. It is predominant upslope but secondary smectites dominate in the Vertisols. Free Fe-oxides are abundant in all soils but slightly more abundant in the upslope soils. Whereas serpentines hold Ni in a similar and restricted range in every soil (approx. 0.3 %), Ni contents in smectites may vary a lot and Mg-rich and Al-poor smectites in the Vertisol could hold up to 4.9 % Ni. Ni was probably adsorbed onto amorphous Fe-oxides and was also exchangeable in secondary smectites. High availability of Ni in soils was confirmed by DTPA extractions. However, it varied significantly along the toposequence, being higher in upslope soils, where Ni-bearing amorphous Fe-oxides were abundant and total organic carbon higher and sensibly lower downslope on the Vertisols: NiDTPA varied from 285 mg kg(-1) in the surface of soil I (upslope) to 95.9 mg kg(-1) in the surface of Fluvic Cambisols. Concentration of Ni in Alyssum murale shoots varied from 0.7 % (Hypereutric Cambisols) to 1.4 % (Hypereutric Vertisol). Amazingly, Ni uptake by A. murale was not correlated to NiDTPA, suggesting the existence of specific edaphic conditions that affect the ecophysiology of A. murale upslope.

Current status and challenges in developing nickel phytomining: an agronomic perspective

“…Soil Ni availability is mainly controlled by the mineralogy and Nibearing mineral phases Chardot et al 2007;Quantin et al 2001). In strongly leached ultramafic soils, such as in Ferralsols, generally the Ni phytoavailability is low (Bani et al 2014;Cheng et al 2011;Das et al 1999;Echevarria et al 2006;Massoura et al 2006;Raous et al 2010;Raous et al 2013). However, in clay-mineral rich young soils (Cambisols) and saprolite materials, the Ni phytoavailable fraction is generally high (Raous et al 2010).…”

“…The sequestration mechanisms for Ni is distinct from Ca handling or storage in Ni hyperaccumulator plants (Broadhurst et al 2004a); but a positive correlation exists in the foliar concentrations of Ca and Ni in some 'metal crop' species (van der Ent and Mulligan 2015). Nickel hyperaccumulator species absorb more Ca relative to Mg, which leads to high Ca:Mg ratio in the leaf tissues (Bani et al 2014); this selective Ca accumulation from soils with very low Ca:Mg ratios substantially reduces Mg and Ni toxicity (Kruckeberg 1991). Unless Ca is actually deficient, Ca addition has little effect on the Ni concentration in the above-ground biomass and shoot yield as well as root-to-shoot translocation of Ni, but may increase Ni tolerance (Chaney et al 2008).…”

Weathering and vegetation controls on nickel isotope fractionation in surface ultramafic environments (Albania)

“…Two soil profiles ( Fig. SI-S1) representative of ultramafic soils in Albania (Bani et al, 2014) were sampled at 1200 m.a.s.l. at Qaftë Shtamë (QA, average annual rainfall of 850 mm and T of ∼11 • C) and at 600 m.a.s.l.…”

“…The A P (0-15 cm), B S (60-70 cm) and C (100-110 cm) horizons were sampled. The soil pH for the Vertisol varies from 6.8 to 8 (Bani et al, 2014). The bedrock was also sampled at each site.…”

“…The type of soil derived, its location in the toposequence, and the Ni content of weathered serpentine clays and Fe-oxides, can all govern the availability of Ni in the different soil horizons (Lee et al, 2003). For instance, the Ni contents of primary minerals (e.g., chlorite, antigorite) are relatively low compared to secondary minerals such as goethite or smectite (Bani et al, 2014). Ni enrichment in the weathered products mainly results from adsorption and Mg-Fe substitution processes (Butt and Cluzel, 2013).…”