Methodology for landscape evaluation and environmental rehabilitation of mining areas using aid decision models

Abstract

A reclamation and a cultural strategy were developed in abandoned tailing ponds. The first objective was to identify species for phytostabilization purposes in order to create a new native vegetation cover able to immobilize and retain metals and reduce erosion. For these reasons four native plants were identified near the tailing ponds in the Avenque stream, Osyris lanceolata, Lavandula dentata, Pistacea lentiscus and Chamaerops humilis and accumulation of trace elements in root, stem or shoot were investigated. Metal concentrations were very variable. In general, in O. lanceolata and C. humilis, metal levels were highest in the roots, whereas in L. dentata and P. lentiscus, highest metal levels were in shoots. Therefore, the use of O. lanceolata and C. humilis in phytostabilization can contribute to metal-immobilization and prevent them from becoming available for biota. Besides, a greenhouse pot experiment was conducted to evaluate the potential use of six native species Nerium oleander L., Cistus albidus L., Pistacia lentiscus L., Lavandula dentata L., Rosmarinus officinalis L. and Thymus vulgaris L. for phytostabilization of acidic mine soils. The selected plants were grown in mine tailing soil, unamended (TS) and amended with calcium carbonate and pig manure (ATS), and in a reference unpolluted substrate for control (CT); plant growth, root characterization, soil trace elements contents, and their accumulation in plants were measured. Results indicate the application of amendment reduced the soil exchangeable and extractable fraction concentrations of trace elements in ATS compared with TS, mainly for As, Cd and Pb. The tested species directly contributed to the immobilization of trace elements in the soil. Although, all the species accumulate metals, levels were below toxicity thresholds. Thus, these species fulfil the criteria to be used for phytostabilization purposes, aided by application of amendments. Once tested, the selected native vegetation with potential phytostabilization ability was planted in one of the tailing ponds. The second objective was to reduce risks related to heavy metal mobility and increase fertility. Thus, marble waste and pig slurry were applied to the surface of the tailing pond. As a result, pH increased until neutrality, and the bioavailable metal fraction significantly reduced, increasing the levels of nutrients and organic matter. The third objective was to give the tailing pond a new recreational and educational use. For this purpose a network of itineraries, viewpoints, access areas and a museum area were created to allow the visitor to observe the reclamation of a degraded mining area. In this context, guidelines for action, and a methodology that can be employed for the regeneration of any area with similar characteristics were established. For this reason the landscaping project of the two abandoned tailing ponds is accompanied by a Decision Aid Model which will serve as a benchmark for future mine rehabilitation projects.