Mine tailings soils with different vegetation cover respond unequally to forecasted climate change conditions: an experimental approach simulating elevated CO2 and temperature

Abstract

Metalliferous mine wastes from ore processing were often stored as slurries in open air piles known as mine tailings. These tailingstypically present harsh conditions for biota, including high salinity, low nutrient and organic matter content, poor edaphic structure, andelevated concentrations of potentially toxic metals and metalloids. Conventional restoration strategies (technical reclamation) usuallyinvolve waste capping with clean material and afforestation. As a nature-based alternative, phytomanagement (particularly phytostabilization) supports plant growth directly on mine wastes. This approach can benefit from studying native vegetation that spontaneouslycolonizes tailings and underlying soils (passive restoration). Since restoration aims to reduce risks to human populations and enhancelong-term environmental quality, it is crucial to assess how tailing soils, whether technically restored or spontaneously colonized byvegetation, respond to climate change.In this work, we experimentally assessed physicochemical and biological changes in soils from technically restored and spontaneouslycolonized tailings under simulated climate change conditions. For each tailing type, soil samples were collected beneath shrub and pinetree vegetation in the former metal mining district of La Unión-Sierra de Cartagena (Cartagena, SE Spain). Plastic pots were filled with850 g of each of the four soil types and placed in climate-controlled chambers for four months (two months simulating spring conditionsand two simulating summer conditions). Climate simulations were based on IPCC projections for the Mediterranean basin incorporatingatmospheric CO2 levels and air temperature. Three scenarios were tested: current conditions (400-500 ppm CO2, current temperature);moderate warming (700 ppm CO2, +3 °C); strong warming (1000 ppm CO2, +5 °C). A range of physicochemical and biological parameters was assessed in soils samples collected at the end of each simulated season. Soil responses varied across climate scenarios andparameters and were influenced by both tailing type and vegetation cover. The findings highlight the need to integrate climate changeprojections into future mine tailings restoration strategies