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Wetlands are highly effective systems in removing large amounts of N from waters, preventing eutrophication processes. However, when wetlands are polluted by metal-mine wastes their capacity to act as green filters may be diminished. The objective of this study was to evaluate the effect of liming and plants (Sarcocornia fruticosa and Phragmites australis) on the removal of NO3 − from eutrophic water in slightly acidic, wetland soils polluted by metal-mine wastes. Simulated soil profiles were constructed and six treatments were assayed: (1) no liming + no plant, (2) no liming + S. fruticosa, (3) no liming + P. australis, (4) liming + no plant, (5) liming + S. fruticosa and (6) liming + P. australis. Three horizons were differentiated: A (never under water), C1 (alternating flooding-drying conditions) and C2 (always under water). The eutrophic water used to flood the soil profiles was enriched in N and organic carbon (pH ∼ 7.5, electrical conductivity ∼ 11 dS m−1, NO3 − ∼ 234 mg L−1 and dissolved organic carbon ∼ 106 mg L−1). The pH, Eh and concentrations of dissolved organic carbon (DOC), N–NO3 − and N–NH4 + were measured regularly for 18 weeks. Liming stimulated the growth of plants, especially for S. fruticosa (20-fold more plant biomass than without liming), increased the soil pH and favoured the decline of the Eh values, enhancing the removal of NO3 − via denitrification. Of all the treatments assayed, liming + S. fruticosa was the only treatment that removed almost completely the high concentration of NO3 − from the eutrophic flooding water, reaching ∼1 mg L−1 N–NO3 − at the end of the experiment, at all depths. The higher content of DOC in the pore water of this treatment could explain this behaviour, since more labile carbon was available to the soil microorganisms in the rhizosphere, favouring NO3 − removal through denitrification processes. However, the treatment liming + P. australis (2-fold more plant biomass that without liming) did not remove completely the high concentrations of NO3 − from the eutrophic water, except in the C2 horizon – which was permanently under water. Hence, our results show that the effectiveness of liming, regarding the removal of NO3 − from eutrophic flooding water in wetland soils polluted by metal-mine wastes, depends on the presence of plants, their growth and the production of organic compounds in the rhizospheric environment. [Copyright &y& Elsevier]

Abstract: The aim of this study was to identify the effectiveness of liming in combination with vegetation for the recovery of slightly acidic, saline soils of eutrophic wetlands affected by mine wastes, under fluctuating flooding conditions. Simulated soil profiles were constructed and four treatments were assayed under greenhouse conditions: control, only plant, only liming, and liming and 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 pH, Eh, salinity, and the concentrations of dissolved organic carbon and soluble metals were measured regularly for 18 weeks. Liming favoured the growth of S. fruticosa, an increase in pH and a fall in Eh. The amendment was effective for reducing Mn, Zn, and Cd in pore water of bare soils, but not Cu and Pb. In the treatment with liming and plant, the growth of S. fruticosa counteracted the effect of the amendment, strongly increasing the concentrations of metals in pore water and distributing them along the soil profile. Hence, the combined use of liming and plants may increase the risk of metals mobilisation. [Copyright &y& Elsevier]

Abstract: The aim of this study was to evaluate the combined effects of liming and behaviour of Sarcocornia fruticosa as a strategy of phytomanagement of metal polluted salt marsh soils. Soils were taken from two polluted salt marshes (one with fine texture and pH∼6.4 and the other one with sandy texture and pH∼3.1). A lime amendment derived from the marble industry was added to each soil at a rate of 20gkg−1, giving four treatments: neutral soil with/without liming and acidic soil with/without liming. Cuttings of S. fruticosa were planted in pots filled with these substrates and grown for 10 months. The pots were irrigated with eutrophicated water. As expected, lime amendment decreased the soluble metal concentrations. In both soils, liming favoured the growth of S. fruticosa and enhanced the capacity of the plants to phytostabilise metals in roots. [Copyright &y& Elsevier]