Liming and vegetation favor Fe-mobilization in eutrophic wetland soils affected by mine wastes

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 ∼18 mg L−1 without liming and ∼6 mg L−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 ∼10 mg L−1 in the A horizon and ∼5 mg L−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.

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► Liming favored an increase in pH and a fall in Eh in metal-polluted wetland soils.
► Sarcocornia fruticosa by itself had little effect on soluble Fe contents.
► Liming decreased soluble Fe in acidic bare soils, but not in acidic vegetated soils.
► Liming with Sarcocornia fruticosa strongly increased soluble Fe in neutral soils.