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This study aimed at assessing the effects of increased air temperature and reduced soil moisture content on the multi-generation toxicity of a soil polluted by metal/metalloid mining wastes. Enchytraeus crypticus was exposed to dilution series of the polluted soil in Lufa 2.2 soil under different combinations of air temperature (20 °C and 25 °C) and soil moisture content (50% and 30% of the soil water holding capacity, WHC) over three generations standardized on physiological time. Generation time was shorter with increasing air temperature and/or soil moisture content. Adult survival was only affected at 30% WHC (∼30% reduction at the highest percentages of polluted soil). Reproduction decreased with increasing percentage of polluted soil in a dose-related manner and over generations. Toxicity increased at 30% WHC (>50% reduction in EC 50 in F0 and F1 generations) and over generations in the treatments at 20 °C (40–60% reduction in EC 50 in F2 generation). At 25 °C, toxicity did not change when combined with 30% WHC and only slightly increased with 50% WHC. So, higher air temperature and/or reduced soil moisture content does affect the toxicity of soils polluted by metal/metalloid mining wastes to E. crypticus and this effect may exacerbate over generations. [ABSTRACT FROM AUTHOR]

Highlights: [•] CaCl2-extractable Cu was correlated with dissolved organic carbon. [•] CaCl2-extractable concentrations did not correlate with metal uptake. [•] Pinus halepensis may be used to phytostabilise metal polluted soils in semiarid areas. [•] Areas surrounding tailings were impacted by high metal(loid) concentrations. [Copyright &y& Elsevier]

Abstract: The aim of this study was to evaluate the effects of liming and vegetation on the dynamic of Fe in eutrophic wetland soils affected by mine wastes, under different flooding regimes. Simulated soil profiles were constructed with two types of wastes (pH∼3.1 and ∼6.4) collected from polluted salt marshes and four treatments were assayed: without liming+without plant, without liming+with plant, with liming+without plant, and with liming+with plant. The plant species was the halophyte Sarcocornia fruticosa. Three horizons were differentiated in the profiles: A horizons (never underwater), C1 (alternating flooding–drying conditions), and C2 (always underwater). The pH, Eh, salinity, and the concentrations of DOC and soluble Fe were measured regularly at each horizon for 18 weeks. Liming decreased Fe solubility, mainly in the acidic waste (maximum average concentrations ∼18mgL−1 without liming and ∼6mgL−1 with liming). However, liming also facilitated a drop in Eh, increasing soluble Fe content. Plant rhizosphere re-distributed this Fe, which was accumulated in the upper horizons of the treatments with liming+with plant, particularly in the acidic waste (average concentrations ∼10mgL−1 in the A horizon and ∼5mgL−1 in the C1 and C2 horizons). Therefore, we conclude that the combined use of liming and vegetation enhance the mobilization of Fe in eutrophic wetland soils polluted by mine wastes under alternating flooding–drying conditions. This should be considered for the environmental management of these sites due to the role of Fe-minerals as sink for potentially-harmful compounds. [Copyright &y& Elsevier]

Spontaneous growth of native vegetation in abandoned metal(loid) mine tailings can be valuable for phytomanagement restoration projects. This study aimed to assess the degree to which spontaneous plant colonization of abandoned metal(loid) mine tailings from Mediterranean semiarid areas led to functional soil improvement, and to identify, if possible, a critical level indicating that this functionality was moving towards that of the vegetated soils from the surroundings. Vegetation ecological indexes, plant life forms and species functional roles, together with physicochemical and functional soils parameters, were studied in metal(loid) mine tailings abandoned ~40 years ago and surrounding forests in SE Spain. Vegetation patches showed only small differences in physicochemical parameters related to soil abiotic stress conditions (pH, salinity and metals), regardless of the vegetation. However, vegetation patches with greater species diversity and richness and presence of plants with contrasted life forms and functional traits that facilitate the growth of less stress-tolerant species showed an increase of the soil microbial functionality (higher microbial biomass C, β-glucosidase activity, bacterial metabolic activity and functional diversity). Moreover, these vegetation patches showed a functional soil status comparable to that of the forests outside the mine tailings. In this sense, the present study showed the value of preserving these vegetation patches since they may act as nucleation spots favoring positive plant-soil feedbacks that may help to accelerate the functional recovery of these degraded areas. Furthermore, strategies to promote the creation of new vegetation patches including a variety of species with contrasted life forms and functional traits should be considered in phytomanagement restoration projects for abandoned metal(loid) mine tailings. [Display omitted] • Soil microbial functionality evaluated by CLPP technique. • Similar soil abiotic stress parameters in tailing vegetation patches. • Higher plant diversity-richness, higher scores of functional-related soil parameters. • More diverse and rich vegetation patches had closer soil functional status to forests. • Spontaneously colonized niches are valuable spots for phytomanagement. [ABSTRACT FROM AUTHOR]

Total and inorganic soil P were extracted from a coastal salt marsh in SE Spain receiving eutrophicated water of urban and agricultural origin. The greatest P contents were obtained within the upper 10 cm of soil of those sectors of the salt marsh most affected by urban waste water effluents. Most of the P was extracted using HCl, indicating that it is mainly bonded to Ca compounds. Only in sites with low CaCO3 content was the quantity of P associated with Fe and Al oxides and hydroxides (extracted with NaOH) noticeable. [Copyright &y& Elsevier]

[Display omitted] • Soil metal(loid)s did not hinder spontaneous vegetation colonization of mine tailings. • Spontaneously vegetated metal(loid) mine tailings showed improved soil function. • Similar soil biological activity in vegetated mine tailing sites than in forests. • Vegetated metal(loid) mine tailing can be even less toxic than surrounding forests. • Passive restoration is valuable for phytomanagement of mine tailings. This work studies a set of soil indicators (physical, physico-chemical and biological), evaluated under field and laboratory conditions, in different stages of spontaneous vegetation colonization in abandoned metal(loid) mine tailings from Mediterranean semiarid areas. The results provide evidence about the interest of spontaneous colonization by native vegetation for the phytomanagement of abandoned metal(loid) mine tailings in terms of providing ecosystem functions. Bare soils (B), small groups of pine trees (P), scattered pine trees with shrubs and herbs under the canopy (P + S), and dense patches of pine trees with shrubs and herbs under the canopy (DP + S) were studied inside mine tailings abandoned ≈40 years ago. Besides, pine forests next (FN) and away (FA) from the tailings were also studied. Pioneer and nurse plants were mainly found inside the tailings, although ecological indexes in P + S and DP + S were similar to FN and FA. Pedogenesis evidences such as structure development and increase in cation exchange capacity, organic C and N were found in tailing soils from B to DP + S. However, soil metal(loid)s did not follow the same variation pattern. For example (in mg kg−1): P showed the maximum total Cu (≈277) and Zn (≈17,860), while P + S of As (≈1250) and Pb (≈14,570). B had the maximum water extractable Pb (≈4) and Zn (≈207), while FA of As (≈0.192) and Cu (≈0.149). Soil microbial biomass C, enzyme activity, CO 2 emission, organic matter decomposition and feeding activity of soil dwelling organisms indicated similar, or even higher, biological activity in P + S and DP + S than in FN and FA. In fact, FA showed the highest soil ecotoxicity risk (reduced enchytraeid reproduction). Therefore, mine tailing soils can be effectively modified following spontaneous vegetation colonization, achieving conditions with capacity to provide certain ecosystem functions. Hence, phytomanagement of these tailings should be preceded by a detailed knowledge of the existing spontaneously colonized sites, which should be preserved to take advantage of their potentiality. [ABSTRACT FROM AUTHOR]

Plant selection is a critical issue for the long-term success of phytomanagement projects. The presence of “microenvironments” related to salinity in mine tailings under semiarid climates make halophytes a suitable alternative for phytostabilisation. The goal of this work was to assess the criteria for plant species selection for the phytostabilisation of mining wastes in semiarid areas, focusing on the suitability of the employment of spontaneous halophyte plant species. For this purpose, a comprehensive soil below-plant and plant survey including spontaneous halophyte and non-halophyte plant species were performed in an extensive area covered by mining wastes in SE Spain. The soil samples collected below halophyte plants showed higher electrical conductivity, organic carbon and water extractable salts concentrations than the non-halophyte ones. Zygophyllum fabago and Limonium cossonianum were the most suitable species to colonize the salty micro niches at the tailings while Tamarix canariensis and Atriplex halimus showed the best soil fertility indicators under moderate electrical conductivity values. In general, the halophyte species showed lower metal(loid) concentrations in leaves or shoots than the non-halophyte ones ( e.g . Cistus monspeliensis , Dittrichia viscosa and Helichrysum decumbens ). Oppositely, the leaves of halophyte plant species, specially A. halimus and Z. fabago , showed higher accumulation of Na and Cl which may be of interest to effect the long term desalination of the tailings. The interest of employing halophytes is not only focused on metal(loid)s tolerance but also in the high potential for soil improvement (organic matter accumulation, desalination). The positive effects of combining halophyte with non-halophyte plant species may enhance the long-term sustainability of the plant community. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to assess the effectiveness of combining liming and vegetation for the phytomanagement of strongly acidic, saline eutrophic wetlands polluted by mine wastes. Simulated soil profiles were constructed and four treatments were assayed: without liming+without plant, without liming+with plant, with liming+without plant and with liming+with plant. The plant species was the halophyte Sarcocornia fruticosa. Three horizons were differentiated: A (never under water), C1 (alternating flooding–drying conditions) and C2 (always under water). The soluble Cd, Cu, Mn, Pb and Zn concentrations were measured regularly for 18weeks and a sequential extraction procedure was applied at the end of the experiment. Liming was effective (between ∼70% and ∼100%) in reducing the soluble Zn, Cu and Pb. In contrast, soluble Mn and Cd increased with liming, especially in the treatment with liming+with plant, where the concentrations were 2-fold higher than in the non-limed treatments. The amendment increased the contents of Zn, Mn and Cd bound to potentially-mobilisable soil fractions at the expense of the most-environmentally-inert fractions. Hence, the combined use of liming and vegetation may increase the long-term environmental risk of metals solubilisation. [Copyright &y& Elsevier]

Abstract: We studied the germination responses of Arthrocnemum macrostachyum, Juncus acutus and Schoenus nigricans to saline stress caused by different salt types. The germination percentage and mean time to germination data were obtained by incubating seeds for 30d in 1, 2, 3, 4 or 5% saline solutions of NaCl, MgCl2, MgSO4 and Na2SO4 at 30/20°C and with a 12h photoperiod. A. macrostachyum was the most tolerant species to salinity during the germination (65% in 2% NaCl). S. nigricans showed the lowest germination (none germinated in salt and only 26% in distilled water). J. acutus showed intermediate behaviour between the two above species, its germination being inhibited by high salt concentrations. The sulphates had less inhibitory effect than the equivalent chloride concentrations. [Copyright &y& Elsevier]

Abstract The suitable phytomanaging of mine tailings not only requires an improvement of soil fertility but also the assessment of the biotic interactions between the selected plant species. This study aimed to evaluate the effect of an organic amendment on the response of two plant species of contrasting habit, a tree, Pinus halepensis and a grass, Piptatherum miliaceum growing on a metal(loid)-contaminated substrate collected from mine tailings. Pots containing single plant individuals or their combination, with and without organic amendment (at 10% rate), were established and grown in a greenhouse for 13 months. Plant biomass, foliar ionome, leaf δ15N and metal(loid) concentrations were measured at the end of the experiment. The amendment alleviated P deficiency in the substrate and strongly stimulated biomass production by both plant species (10-fold for pine; 90-fold for the grass), leading to more balanced N/P ratios in leaves (especially for the grass). Co-culture with the grass negatively affected pine growth, decreasing total biomass and leaf δ15N values and inducing severe N deficiency (leaf N/P ratio<10). In contrast, co-culture with pine improved the nutrient status and growth of the grass, but only under non-amended conditions. Needle metal(loid) concentrations in P. halepensis were affected by both amendment addition and co-culture with the grass. High biomass growth with low metal(loid) concentrations in P. miliaceum leaves for the amended treatment makes this grass species suitable for the phytomanagement of metal(loid) polluted tailings, since it achieves high biomass production together with low concentrations of metal(loid)s in edible/senescent parts. Highlights • Co-culture modulated plant performance in amended treatments. • Co-culture with the grass P.miliaceum negatively affected pine (P.halepensis) growth. • P.miliaceum showed higher competitive ability when co-cultured with P.halepensis. [ABSTRACT FROM AUTHOR]

Abstract: Salt marshes near urban, industrial and mining areas are often affected both by heavy metals and by eutrophic water. The aim of this study was to assess and evaluate the main processes involved in the decrease of nitrate concentration in pore water of mine wastes flooded with eutrophic water, considering the presence or absence of plant rhizhosphere. Basic (pH∼7.8) carbonated loam mine wastes and free-carbonated acidic (pH∼6.2) sandy-loam mine wastes were collected from polluted coastal salt marshes of SE Spain which regularly receive nutrient-enriched water. The wastes were put in pots and flooded for 15 weeks with eutrophic water (dissolved organic carbon ∼26mgL−1, PO4 3− ∼23mgL−1, NO3 − ∼180mgL−1). Three treatments were assayed for each type of waste: pots with Sarcocornia fruticosa, pots with Phragmites australis and unvegetated pots. Soluble organic carbon, nitrate, soluble Cd, Pb and Zn, pH and Eh were monitored. But the 2nd day of flooding, nitrate concentrations had decreased between 70% and 90% (equivalent to 1.01–1.12gN-NO3 − m−2 day−1) with respect to the content in the water used for flooding, except in unvegetated pots with acidic wastes. Denitrification was the main mechanism associated with the removal of nitrate. The role of vegetation in improving the rhizospheric environment was relevant in the acidic wastes because higher sand content, lower pH and higher soluble metal concentrations might strongly hinder microbial activity Hence, revegetation of salt marshes polluted by acidic sandy mining wastes might improve the capacity of this type of environment to act as a green filter against excessive nitrate contents flowing through them. [Copyright &y& Elsevier]

Abstract: The occurrence of mining areas in the vicinities of salt marshes may affect their ecological functions and facilitate the transfer of pollutants into the food chain. The mobilisation of metals in salt marsh soils is controlled by abiotic (pH, redox potential) and biotic (influence of rhizosphere) factors. The effect of the rhizosphere of two plant species (Sarcocornia fruticosa and Phragmites australis) and different flooding regimes on potentially harmful metals and As mobilisation from salt marsh soil polluted by mining activities were investigated (total concentrations: 536mgkg−1 As, 37mgkg−1 Cd, 6746mgkg−1 Pb, 15,320mgkg−1 Zn). The results show that the changes in redox conditions (from 300mV to −100mV) and pH after flooding and rewetting periods may mobilise the contaminant elements into soil solution (e.g., 100μgL−1 Cd, 30μgL−1 Pb, 7mgL−1 Zn), where they are available for plants or may be leached from the soil. Drying periods generated peaks of concentrations in the soil solution (up to 120μgL−1 Cd and 50μgL−1 Pb). The risk assessment of As and metal-polluted salt marshes should take into account flood dynamics in order to prevent metal(loid) mobilisation. [ABSTRACT FROM AUTHOR]