Lysimeter monitoring as assessment of the potential for revegetation to manage former iron industry settling ponds

• The Technosol provides a regulating service by retaining water and metals.
• High retention capacity is due to soil composition and physico-chemical properties.
• Dense and deeply-rooted vegetation cover limits water and solute fluxes.
• Settling ponds of iron industry could be managed by monitored revegetation.

To assess the impact of metal-rich brownfields on groundwater quality, the fluxes in a Technosol developed on a former iron industry settling pond were studied. Intact soil monoliths (1 m2 × 2 m) were extracted and placed in lysimeters. Dynamics of fluxes of metals and solutes under varying vegetation cover were monitored over the course of four years. Soil hydraulic properties were also determined. Results showed that the Technosol has a high retention capacity for water and metals, in relation to its mineral components and resulting chemical and physical properties. As a consequence, metal fluxes were limited. However, soluble compounds, such as SO42 −, were found at significant concentrations in the leachates. The presence of a dense and deeply-rooted vegetation cover limited water- and solute-fluxes by increasing evapotranspiration and water uptake, thereby reducing the risks of transfer of potentially toxic compounds to local groundwater sources. However, vegetation development may induce changes in soil chemical (e.g. pH, redox potential) and physical properties (e.g. structure), favoring metal mobilization and transport. Revegetation is a valuable management solution for former iron industry settling ponds, provided vegetation does not change soil physico-chemical conditions in the long term. Monitored natural attenuation is required.