Ecological impacts and ecosystem response in an old mining area of SE Spain: learning lessons for phytomanagement

Resumen

This presentationshows the results of a study in which field and greenhouse works wereperformed in an old mining area (Cartagena-La Unión SE Spain). Theobjective was to understand the plant colonisation mechanisms in sitesaffected by mine wastes (tailings and polluted salt marshes) to takeadvantage of the natural processes for phytomanagement pruporses.Field works studied the environmental gradients, soil-plant relationships,plant-favourable edaphic niches, key species, seed bank and metal(loid)accumulation in soils and plants. Greenhouse works gave informatonabout the effects of soil amendments (municipal waste refuse -MWR-,biochar -B- and liming -L-) on metal(loid) geochemistry and plantgrowth. Vegetation colonisation was favoured by the existence ofedaphic niches with favourable conditions; soil salinity played a keyrole. In the mine tailings patches with sandy texture and lower salinityshowed the most favourable conditions for pioner vegetation (grassesand shrubs), improving the nutritional and microbiological status ofrhizospheric soils, while those more saline and with fine texture showedno plants. Late successional stages with climax vegetation were found aspart of the so called fertility islands, with a key role of trees. In the saltmarsh the most saline and wettest sites were the most affected by themine wastes, showing no vegetation. Plant colonisation of mine tailingbare soils was strongly limited by the absence of seeds, while in the saltmarsh by the absence of germination of the present seeds. Plantsaccumulated more metal(loid)s in belowground tissues. Greenhouseexperiments showed that in the mine tailings MWR improved soilfertility and plant growth, but enhance metal mobility, while B increasedwater holding capacity and reduced metal mobility, but was lesseffective than MWR providing nutrients. Under hydric conditions (saltmarsh) B and L amendments favoured decreasing Eh values, increasingmetal mobility, especially in the presence of vegetation. The use ofspecific remediation measures is strongly advised in mine tailings andsites polluted by mine wastes. The presence of diverse plant species,with contrasting strategies to cope with multiple stresses, may result in amore efficient employment of the water resources and a higherbiodiversity. The effectiveness of different amendments (organic andinorganic) may be influenced by the soil characteristics but also by thebiogeochemical conditions of the target site